AFM Adjustment
- Amskeptic
- IAC "Help Desk"
- Status: Offline
AFM Adjustment
AIR FLOW METER ADJUSTMENT
Quicky overview to help you understand these things.
The throttle plate is the sole device that controls the amount of air entering the engine (except for the throttle bypass that allows us to adjust idle *speed* with a simple screw "gate").
The airflow meter is a *passive* device that measures, but does not "control" airflow. The measurement of the airflow determines the fuel ratio your engine has to work with. Any air that gets into the engine that has not been measured by the flap is called "unmetered air" and it will make your fuel ratio lean (this includes the mixture bypass which allows us to adjust the idle *mixture* with a simple screw "gate").
This adjustment will have great bearing on the driveability and reliability of your L-Jetronic fuel injected Volkswagen. I will endeavor to explain this as clearly as possible, but if you do not "get it", do not attempt to adjust your AFM. There is a very real chance that you could inadvertently turn the internal combustion engine of your beloved Volkswagen into an exhaust valve bisecting blowtorch, or perhaps you would prefer a smog-belching coal plant wannabe.
You might have noticed that every book dealing with carburetor and fuel injection adjustments always tells you to adjust the valves, points and timing before touching any fuel system adjustment. There is a good reason for this. A fuel injection or carburetor adjustment CANNOT affect valves or timing . . . but valves and timing sure can affect carburetion and fuel injection!
Prerequisites:
* Comprehension of CW (ClockWise) and CCW (CounterClockWise)
* Valve Adjustment - consistency counts, valve cover gasket must be correctly installed
* Points/Timing - 25* to 28* BTDC @ 3,000 or 3,200 or 3,400 rpm with an idle timing of 7.5 or below before you attach your vacuum hose(s) back on.
* Temp Sensor II - check for secure install in head (10 ft/lbs) and clean connector DeOx gel is a good connector deoxidant
* Warm Engine - below checks and a 10 minute drive on top of that, take 20 if it is cold out
* Fuel Pressure - make sure that the regulator is throttling back the pressure at idle
* Vacuum Leaks? - injector small donut seals, intake runners, auxiliary air regulator elbow, breather gasket and hose, dipstick hat seal and boot, brake booster circuit (check by just pulling it off and blocking, if engine runs differently, check further)
* Preset Mixture Screw (see Diagram 2 (C))
Turn regular or 5mm Allen screw CW until it seats (NOTE HOW MANY TURNS).
This shuts off the air bypass around the flap. Turn it out CCW 4 1/2 turns. This is the midpoint which gives the best flexibility in the future when you need to do little trim adjustments. This preset may make the engine run poorly. Sorry. Someone has most likely turned it down (thus richening the mixture) in a gleefully irresponsible way to avoid finding vacuum leaks in the past.
Remove black plastic cap from the top of the AFM (see Diagram 1). If it is untouched, it will take some work to get the cap off. A wide chisel blade or big screwdriver will help you pry it off. First, cut the bead of sealant around the perimeter with a razor blade. Pry at the upper right edge near the connector and apply broad slow pressure upwards, allow it to slowly release before you finally pry it all the way off.
While you are here, check to see that the little tiny contact tips on the wiper are landing on good black track through the entire sweep. If you see white plastic showing through, roll the contact strips as per Diagram 1.
(fusername wrote:
there is a cleaner/lubricant spray available at Radio Shack for the wiper board.
The pressure set from the factory of the wiper arm on the track is very specific. The contact area is so small between the wiper and the track that small differences in load will make enourmous pressure differences at tiny little tip of that arm.
For this reason he strongly recommends NOT to touch the wiper arm, and instead to loosen the screws holding the board in place, then simply shift the board and tighten them up again. )
DIAGRAM 1
STEP ONE
Ask The Engine What It Wants
You ASK by moving the little wiper inside the box barely a 1/4" in either direction with your fingers.This will temporarily provide more fuel (CCW), or less fuel (CW).
The engine REPLIES by either speeding up or slowing down. Speeding up means that the engine LIKES what you provided. Slowing down means that it does not care for what you gave it. Note that if you move the wiper too much in either direction the engine will slow down or stall, telling you nothing but that you are too ham-handed. Be subtle.
If you move the wiper CCW and the engine speeds up, then the current status of the mixture (i.e. when you let go) is LEAN.
If you move the wiper CW, and the engine speeds up, the current status of the mixture (when you let go) is RICH.
At idle, if the wiper moves 1/4 CCW and a 1/4 CW with no change in rpm, you'd think we were in the sweet spot, but we want it slightly leaner than that. We want the engine at the edge of lean, but not into the lean.
A) Ask what the engine wants at idle, make a note of its reply.
(see Diagram 4 for a preview)
B) Ask what it wants at 2,800-3,000 rpm, make a note of its reply.
(see Diagram 4 for a preview)
You must hold the throttle open with mechanical means for the high speed test, no human involvement. A screwdriver judiciously applied to the throttle lever and wedged somewhere that works will be adequate, sometimes a crunched up popsicle stick can be used. The high speed response is sometimes hard to glean through all the racket, a good tach/dwell meter will be helpful if your ears cannot distinguish.
At speed, we also want the engine slightly lean, i.e. when you move the wiper a tad CW, the speed goes down immediately, but doesn't break up, and when we move it CCW, the speed goes up a little but not desperately. If it remains steady when you move the wiper CCW, try to lean it just a tiny bit as per below steps.
C) Look at your engine's responses. They determine which adjustments you make and in what order (preview Diagram 4).
DIAGRAM 2
There are three potential adjustments that gives us complete control over the engine's fuel mixture from idle to high speed (and it is totally easier than setting float levels and changing out idle jets and air correction jets and main jets and pilot jets and accelerator pump jets like those poor carburetor people have to):
(A) Static.
This adjustment repositions the wiper on the shaft that holds the flap. This adjustment richens or leans the entire fuel map.
(B) Dynamic.
This adjustment tightens or loosens the flap return spring. This adjustment has a greater effect upon the high rpm/load end of the map.
(C) Mixture Screw.
This primarily affects the final idle mixture, down at the bottom of the map and we do it last.
STEP TWO
Adjust The Airflow Meter
Please NOTE ALL STARTING POINTS beforehand.
Please NOTE ALL STARTING POINTS beforehand.
Please NOTE ALL STARTING POINTS beforehand.
A dab of paint or fingernail polish is good.
DIAGRAM 3
A) Static Adjustment:
It changes the mixture across the entire range of the fuel map from low to high rpm. This is a linear adjustment, and it is very powerful. If you make it richer (CCW) then the idle is richer, the mid range is richer, the top of the range is richer.
If you move it CW in relation to the flap, you make it leaner from idle all the way to the top of the range. (see Diagram 3)
Try to adjust in increments of just one tooth at a time. The screw is often trapped by a blob of silicone glue. Mark your initial position, hold the wiper still while you crack the screw loose and clean the silicone glob off. Use your little screwdriver to pry wiper rich or lean using the metal clamp screw threads as your fulcrum. (see Diagram 4)
B) Dynamic Adjustment:
this changes the resistance to airflow via the clockspring wound up inside the black cog. It has greater effect upon the higher rpms and heavier loads, so it changes the curve of the fuel map. CCW makes the spring unwind, get weaker, have less resistance, and therefore allows the flap to call for more fuel more easily, thus richening your mixture. Moving the cog CW makes the spring stronger, so the flap is unable to move as much in the breeze to call for more fuel, thus leaning out the mixture, particularly at higher rpms and loads. (see Diagram 3)
Mark your initial spot. Use a biggish regular screwdriver blade to pry the cog teeth in the direction you want to go while at the same time prying the metal wire away from the tooth that it is currently holding. You can go one tooth at a time very nicely. Try three teeth as your basic unit of adjustment, then as you become subtly attuned, you can go one tooth at a time as you reach fuel mixture nirvana. (see Diagram 4)
C) Mixture Screw:
this is merely a gate that closes the air bypass around the flap. Think of it this way. If the engine has 100 units of air (requested by the throttle plate remember) and the mixture screw is closed clockwise, all 100 units of air are metered and provided with fuel as determined by the ECU. If you open the mixture screw CCW, the bypass could allow 50% of the air to escape detection by the flap. The flap/wiper assembly tells the ECU to give 50 units worth of fuel, even though 100 units still goes to the engine. Vacuum leaks fool the ECU the same way. And if your AFM has the mixture screw bypass completely closed when you get to it, guess what? Someone else has been fooled too.
We start at the midpoint here, and then do our very last "trim" adjustment with the mixture screw. The other adjustments here have an effect on the idle every time, even the high speed/load spring adjustment has a shadow effect on the idle. So get the screw in the middle, and you will have enough range to get everybody on the map happy.
(see Diagram3 & 4)
At idle, a perfect adjustment is to have the engine drop immediately when you move the wiper just a smidge CW, and we want it to remain steady or go up just a little if you move it just a tad CCW. We want the engine at the edge of lean, but not into the lean.
At speed, we want the engine slightly lean, i.e. when you move the wiper a tad CW, the speed goes down immediately, but doesn't break up, and when we move it CCW, the speed goes up a little but not desperately. If it remains steady when you move the wiper CCW, try to lean it just a tiny bit.
example 1
...lean idle
...lean high speed
*** adjust (A)Static CCW a tooth.
This adjustment moves the whole mixture progression from idle to high load/rpm.
example 2
... rich idle
... lean high speed
*** adjust Static CW until idle is perfect, then adjust (B)Dynamic CCW to help richen the high speed mixture, then trim unintended consequence (probably a tad richer) to the idle with the (C)Mixture screw.
example 3
... lean idle
... rich high speed
*** adjust (A) CCW for perfect idle, then tighten (B) CW to help lean out the high speed mixture, then trim the unintended consequence (probably a tad leaner) to the idle with (C)
example 4 (not illustrated)
... perfect idle
... rich high speed
*** adjust (B) CW until high speed is perfect, then trim now lean idle with (C). But let's say that you have to almost bottom out the (C) Mixture Screw to save the idle. Feel free to put mixture screw back to 4 1/2 turns out, and richen the (A)Static to get your perfect idle back. Now recheck the high speed, probably rich again right? Hit the (B)Dynamic a few more clicks lean.
DIAGRAM 4
STEP THREE
Adjust The Fuel Pump Shutoff
If you have moved the wiper (A)Static adjustment, you will have to check to make sure that the fuel pump shuts off with the engine off. Bend the contact arm (with a "backwrench" along the rod, so that you do not accidentally change the adjustment of the wiper) so that the little copper contacts are spread apart by a millimeter when the wiper is parked.
(see Diagram 2 green/red stripe)
Other Considerations:
ACCELERATION
Rev the engine in a short sharp little burst. Look at the wiper. It overshoots due to momentum. This is your "accelerator pump". The engineers have weighted this wiper to do exactly that. If you end up with *hesitation* under sharp acceleration, you can actually help things out by weakening the spring a little and using the other adjustments to pull the other parameters as close to best as you can get:
CCW (B) 6 clicks, CW (A) 1 tooth for exactly the same mixture at 3,000 rpm, and now you have to ask the (C) Mixture Screw to please really help out here (you'd probably have to lean a bit)
Did you make the hesitation worse? Well . . . it could be a rich flat spot! If that is the case, the wiper is overshooting too much. Experiment! Reverse above. Now go 6 clicks in the opposite direction towards stronger with (B). CCW 2 teeth with (A) for a net richen of 1. Trim your idle. Go test acceleration. Better? Good. No change? Revert to your last known good settings.
COLD START
A common syptom is an L-Jet that bogs after cold start. Low idle speed and balky behavior *can* be too rich or too lean. So get back there and ask the engine at the wiper. If your Temp Sensor I and II are exactly within specifications, you might have a mixture adjustment that is too lean or too rich at idle, and the compensation provided by the ECU may be leaving the parameters. If cold idle is too rich, try going lean at (A) and see if that cleans up the cold idle. THEN with a warm engine, adjust the (C) Mixture Screw only to save the warm idle as necessary and adjust the (B) Dynamic to save the high speed. The AAR is all metered air, remember.It's "intake" is below the AFM.
SPARK PLUGS
It is a very good idea to check the plugs after an AFM adjustment. Hit the highway and get a good 40 miles of your favorite cruising speed. Find a rest area pull-off and cut the engine at the exit. Coast to a shady spot if that is your thing (I aim for the sunny spots) and let the engine cool. Take a nap, a walk, play frisbee with the dog, wash the windows, and when the engine has cooled to luke warm, pull a plug and look for white powder on the ground electrode, or a bleached white insulator under the center electrode. This would be too lean.
If so, check a plug across the engine. Same? Pull another plug. Same? Then do the AFM adjustment procedure again with an emphasis on the high speed rpms as you move the wiper, see if you can get a no-rpm-change zone where moving the wiper CCW or CW has no effect on rpms, that would be the "sweet spot" mentioned above. Recheck the plugs after 100 miles to give time for a picture to emerge. New plugs are almost impossible to read until they get some miles on them. If you have only one or two plugs lean, and the others are tannish, then you need to ask if there is an injector that is dirty, or a seal/intake gasket/runner that is leaking at that cylinder, or in today's world, the spark plug itself may be leaking between the shell and the insulator. If you have a CHT thermocouple ring under the #3 plug, note that leaks are common here, and they will contribute to a lean read on that cylinder, not to mention those scary numbers on your CHT gauge.
LM-1 VERIFICATION/SMOG TEST
Always have a thoroughly warm engine on Smog Test Day, with a fresh air filter, fresh oil, and block the fuel evaporative hose to the air filter from your canister discreetly please.
The above procedure should give you very close to a 13.5- 14.0 ratio at the no-change-in-rpm wiper 1/4" either way point. If you go 3 clicks CW (lean) with the (B)Dynamic adjustment from there to cover the high speed part of the test,and 1/2 turn CCW of the (C) Mixture Screw, you will likely slip under the 2.5% CO limit but feel free to lean out further on Smog Test Day if your engine runs well. You want lean and smooth. Too lean, and you get lean misfires HC fail.
Please inform me of any LM-1 ratios vs Smog Test percentages that you run across. So far, my experience has shown that the VW engine produces best power at 13.5, can idle in the 14s nicely, and will show 17-20 while puttering around town. There is a fuel shut-off when the ECU determines that the engine is on overrun, i.e. closed throttle and high rpms. This cut-off point can change depending on temperature readings from the sensors, but generally has been around 1,700 rpm. A stoichiometric ratio of 14.7:1 on your tester is a pretty decent place to be for a clean test. When I LM-1 the BobD, I will let you know of my observations.
Quicky overview to help you understand these things.
The throttle plate is the sole device that controls the amount of air entering the engine (except for the throttle bypass that allows us to adjust idle *speed* with a simple screw "gate").
The airflow meter is a *passive* device that measures, but does not "control" airflow. The measurement of the airflow determines the fuel ratio your engine has to work with. Any air that gets into the engine that has not been measured by the flap is called "unmetered air" and it will make your fuel ratio lean (this includes the mixture bypass which allows us to adjust the idle *mixture* with a simple screw "gate").
This adjustment will have great bearing on the driveability and reliability of your L-Jetronic fuel injected Volkswagen. I will endeavor to explain this as clearly as possible, but if you do not "get it", do not attempt to adjust your AFM. There is a very real chance that you could inadvertently turn the internal combustion engine of your beloved Volkswagen into an exhaust valve bisecting blowtorch, or perhaps you would prefer a smog-belching coal plant wannabe.
You might have noticed that every book dealing with carburetor and fuel injection adjustments always tells you to adjust the valves, points and timing before touching any fuel system adjustment. There is a good reason for this. A fuel injection or carburetor adjustment CANNOT affect valves or timing . . . but valves and timing sure can affect carburetion and fuel injection!
Prerequisites:
* Comprehension of CW (ClockWise) and CCW (CounterClockWise)
* Valve Adjustment - consistency counts, valve cover gasket must be correctly installed
* Points/Timing - 25* to 28* BTDC @ 3,000 or 3,200 or 3,400 rpm with an idle timing of 7.5 or below before you attach your vacuum hose(s) back on.
* Temp Sensor II - check for secure install in head (10 ft/lbs) and clean connector DeOx gel is a good connector deoxidant
* Warm Engine - below checks and a 10 minute drive on top of that, take 20 if it is cold out
* Fuel Pressure - make sure that the regulator is throttling back the pressure at idle
* Vacuum Leaks? - injector small donut seals, intake runners, auxiliary air regulator elbow, breather gasket and hose, dipstick hat seal and boot, brake booster circuit (check by just pulling it off and blocking, if engine runs differently, check further)
* Preset Mixture Screw (see Diagram 2 (C))
Turn regular or 5mm Allen screw CW until it seats (NOTE HOW MANY TURNS).
This shuts off the air bypass around the flap. Turn it out CCW 4 1/2 turns. This is the midpoint which gives the best flexibility in the future when you need to do little trim adjustments. This preset may make the engine run poorly. Sorry. Someone has most likely turned it down (thus richening the mixture) in a gleefully irresponsible way to avoid finding vacuum leaks in the past.
Remove black plastic cap from the top of the AFM (see Diagram 1). If it is untouched, it will take some work to get the cap off. A wide chisel blade or big screwdriver will help you pry it off. First, cut the bead of sealant around the perimeter with a razor blade. Pry at the upper right edge near the connector and apply broad slow pressure upwards, allow it to slowly release before you finally pry it all the way off.
While you are here, check to see that the little tiny contact tips on the wiper are landing on good black track through the entire sweep. If you see white plastic showing through, roll the contact strips as per Diagram 1.
(fusername wrote:
there is a cleaner/lubricant spray available at Radio Shack for the wiper board.
The pressure set from the factory of the wiper arm on the track is very specific. The contact area is so small between the wiper and the track that small differences in load will make enourmous pressure differences at tiny little tip of that arm.
For this reason he strongly recommends NOT to touch the wiper arm, and instead to loosen the screws holding the board in place, then simply shift the board and tighten them up again. )
DIAGRAM 1
STEP ONE
Ask The Engine What It Wants
You ASK by moving the little wiper inside the box barely a 1/4" in either direction with your fingers.This will temporarily provide more fuel (CCW), or less fuel (CW).
The engine REPLIES by either speeding up or slowing down. Speeding up means that the engine LIKES what you provided. Slowing down means that it does not care for what you gave it. Note that if you move the wiper too much in either direction the engine will slow down or stall, telling you nothing but that you are too ham-handed. Be subtle.
If you move the wiper CCW and the engine speeds up, then the current status of the mixture (i.e. when you let go) is LEAN.
If you move the wiper CW, and the engine speeds up, the current status of the mixture (when you let go) is RICH.
At idle, if the wiper moves 1/4 CCW and a 1/4 CW with no change in rpm, you'd think we were in the sweet spot, but we want it slightly leaner than that. We want the engine at the edge of lean, but not into the lean.
A) Ask what the engine wants at idle, make a note of its reply.
(see Diagram 4 for a preview)
B) Ask what it wants at 2,800-3,000 rpm, make a note of its reply.
(see Diagram 4 for a preview)
You must hold the throttle open with mechanical means for the high speed test, no human involvement. A screwdriver judiciously applied to the throttle lever and wedged somewhere that works will be adequate, sometimes a crunched up popsicle stick can be used. The high speed response is sometimes hard to glean through all the racket, a good tach/dwell meter will be helpful if your ears cannot distinguish.
At speed, we also want the engine slightly lean, i.e. when you move the wiper a tad CW, the speed goes down immediately, but doesn't break up, and when we move it CCW, the speed goes up a little but not desperately. If it remains steady when you move the wiper CCW, try to lean it just a tiny bit as per below steps.
C) Look at your engine's responses. They determine which adjustments you make and in what order (preview Diagram 4).
DIAGRAM 2
There are three potential adjustments that gives us complete control over the engine's fuel mixture from idle to high speed (and it is totally easier than setting float levels and changing out idle jets and air correction jets and main jets and pilot jets and accelerator pump jets like those poor carburetor people have to):
(A) Static.
This adjustment repositions the wiper on the shaft that holds the flap. This adjustment richens or leans the entire fuel map.
(B) Dynamic.
This adjustment tightens or loosens the flap return spring. This adjustment has a greater effect upon the high rpm/load end of the map.
(C) Mixture Screw.
This primarily affects the final idle mixture, down at the bottom of the map and we do it last.
STEP TWO
Adjust The Airflow Meter
Please NOTE ALL STARTING POINTS beforehand.
Please NOTE ALL STARTING POINTS beforehand.
Please NOTE ALL STARTING POINTS beforehand.
A dab of paint or fingernail polish is good.
DIAGRAM 3
A) Static Adjustment:
It changes the mixture across the entire range of the fuel map from low to high rpm. This is a linear adjustment, and it is very powerful. If you make it richer (CCW) then the idle is richer, the mid range is richer, the top of the range is richer.
If you move it CW in relation to the flap, you make it leaner from idle all the way to the top of the range. (see Diagram 3)
Try to adjust in increments of just one tooth at a time. The screw is often trapped by a blob of silicone glue. Mark your initial position, hold the wiper still while you crack the screw loose and clean the silicone glob off. Use your little screwdriver to pry wiper rich or lean using the metal clamp screw threads as your fulcrum. (see Diagram 4)
B) Dynamic Adjustment:
this changes the resistance to airflow via the clockspring wound up inside the black cog. It has greater effect upon the higher rpms and heavier loads, so it changes the curve of the fuel map. CCW makes the spring unwind, get weaker, have less resistance, and therefore allows the flap to call for more fuel more easily, thus richening your mixture. Moving the cog CW makes the spring stronger, so the flap is unable to move as much in the breeze to call for more fuel, thus leaning out the mixture, particularly at higher rpms and loads. (see Diagram 3)
Mark your initial spot. Use a biggish regular screwdriver blade to pry the cog teeth in the direction you want to go while at the same time prying the metal wire away from the tooth that it is currently holding. You can go one tooth at a time very nicely. Try three teeth as your basic unit of adjustment, then as you become subtly attuned, you can go one tooth at a time as you reach fuel mixture nirvana. (see Diagram 4)
C) Mixture Screw:
this is merely a gate that closes the air bypass around the flap. Think of it this way. If the engine has 100 units of air (requested by the throttle plate remember) and the mixture screw is closed clockwise, all 100 units of air are metered and provided with fuel as determined by the ECU. If you open the mixture screw CCW, the bypass could allow 50% of the air to escape detection by the flap. The flap/wiper assembly tells the ECU to give 50 units worth of fuel, even though 100 units still goes to the engine. Vacuum leaks fool the ECU the same way. And if your AFM has the mixture screw bypass completely closed when you get to it, guess what? Someone else has been fooled too.
We start at the midpoint here, and then do our very last "trim" adjustment with the mixture screw. The other adjustments here have an effect on the idle every time, even the high speed/load spring adjustment has a shadow effect on the idle. So get the screw in the middle, and you will have enough range to get everybody on the map happy.
(see Diagram3 & 4)
At idle, a perfect adjustment is to have the engine drop immediately when you move the wiper just a smidge CW, and we want it to remain steady or go up just a little if you move it just a tad CCW. We want the engine at the edge of lean, but not into the lean.
At speed, we want the engine slightly lean, i.e. when you move the wiper a tad CW, the speed goes down immediately, but doesn't break up, and when we move it CCW, the speed goes up a little but not desperately. If it remains steady when you move the wiper CCW, try to lean it just a tiny bit.
example 1
...lean idle
...lean high speed
*** adjust (A)Static CCW a tooth.
This adjustment moves the whole mixture progression from idle to high load/rpm.
example 2
... rich idle
... lean high speed
*** adjust Static CW until idle is perfect, then adjust (B)Dynamic CCW to help richen the high speed mixture, then trim unintended consequence (probably a tad richer) to the idle with the (C)Mixture screw.
example 3
... lean idle
... rich high speed
*** adjust (A) CCW for perfect idle, then tighten (B) CW to help lean out the high speed mixture, then trim the unintended consequence (probably a tad leaner) to the idle with (C)
example 4 (not illustrated)
... perfect idle
... rich high speed
*** adjust (B) CW until high speed is perfect, then trim now lean idle with (C). But let's say that you have to almost bottom out the (C) Mixture Screw to save the idle. Feel free to put mixture screw back to 4 1/2 turns out, and richen the (A)Static to get your perfect idle back. Now recheck the high speed, probably rich again right? Hit the (B)Dynamic a few more clicks lean.
DIAGRAM 4
STEP THREE
Adjust The Fuel Pump Shutoff
If you have moved the wiper (A)Static adjustment, you will have to check to make sure that the fuel pump shuts off with the engine off. Bend the contact arm (with a "backwrench" along the rod, so that you do not accidentally change the adjustment of the wiper) so that the little copper contacts are spread apart by a millimeter when the wiper is parked.
(see Diagram 2 green/red stripe)
Other Considerations:
ACCELERATION
Rev the engine in a short sharp little burst. Look at the wiper. It overshoots due to momentum. This is your "accelerator pump". The engineers have weighted this wiper to do exactly that. If you end up with *hesitation* under sharp acceleration, you can actually help things out by weakening the spring a little and using the other adjustments to pull the other parameters as close to best as you can get:
CCW (B) 6 clicks, CW (A) 1 tooth for exactly the same mixture at 3,000 rpm, and now you have to ask the (C) Mixture Screw to please really help out here (you'd probably have to lean a bit)
Did you make the hesitation worse? Well . . . it could be a rich flat spot! If that is the case, the wiper is overshooting too much. Experiment! Reverse above. Now go 6 clicks in the opposite direction towards stronger with (B). CCW 2 teeth with (A) for a net richen of 1. Trim your idle. Go test acceleration. Better? Good. No change? Revert to your last known good settings.
COLD START
A common syptom is an L-Jet that bogs after cold start. Low idle speed and balky behavior *can* be too rich or too lean. So get back there and ask the engine at the wiper. If your Temp Sensor I and II are exactly within specifications, you might have a mixture adjustment that is too lean or too rich at idle, and the compensation provided by the ECU may be leaving the parameters. If cold idle is too rich, try going lean at (A) and see if that cleans up the cold idle. THEN with a warm engine, adjust the (C) Mixture Screw only to save the warm idle as necessary and adjust the (B) Dynamic to save the high speed. The AAR is all metered air, remember.It's "intake" is below the AFM.
SPARK PLUGS
It is a very good idea to check the plugs after an AFM adjustment. Hit the highway and get a good 40 miles of your favorite cruising speed. Find a rest area pull-off and cut the engine at the exit. Coast to a shady spot if that is your thing (I aim for the sunny spots) and let the engine cool. Take a nap, a walk, play frisbee with the dog, wash the windows, and when the engine has cooled to luke warm, pull a plug and look for white powder on the ground electrode, or a bleached white insulator under the center electrode. This would be too lean.
If so, check a plug across the engine. Same? Pull another plug. Same? Then do the AFM adjustment procedure again with an emphasis on the high speed rpms as you move the wiper, see if you can get a no-rpm-change zone where moving the wiper CCW or CW has no effect on rpms, that would be the "sweet spot" mentioned above. Recheck the plugs after 100 miles to give time for a picture to emerge. New plugs are almost impossible to read until they get some miles on them. If you have only one or two plugs lean, and the others are tannish, then you need to ask if there is an injector that is dirty, or a seal/intake gasket/runner that is leaking at that cylinder, or in today's world, the spark plug itself may be leaking between the shell and the insulator. If you have a CHT thermocouple ring under the #3 plug, note that leaks are common here, and they will contribute to a lean read on that cylinder, not to mention those scary numbers on your CHT gauge.
LM-1 VERIFICATION/SMOG TEST
Always have a thoroughly warm engine on Smog Test Day, with a fresh air filter, fresh oil, and block the fuel evaporative hose to the air filter from your canister discreetly please.
The above procedure should give you very close to a 13.5- 14.0 ratio at the no-change-in-rpm wiper 1/4" either way point. If you go 3 clicks CW (lean) with the (B)Dynamic adjustment from there to cover the high speed part of the test,and 1/2 turn CCW of the (C) Mixture Screw, you will likely slip under the 2.5% CO limit but feel free to lean out further on Smog Test Day if your engine runs well. You want lean and smooth. Too lean, and you get lean misfires HC fail.
Please inform me of any LM-1 ratios vs Smog Test percentages that you run across. So far, my experience has shown that the VW engine produces best power at 13.5, can idle in the 14s nicely, and will show 17-20 while puttering around town. There is a fuel shut-off when the ECU determines that the engine is on overrun, i.e. closed throttle and high rpms. This cut-off point can change depending on temperature readings from the sensors, but generally has been around 1,700 rpm. A stoichiometric ratio of 14.7:1 on your tester is a pretty decent place to be for a clean test. When I LM-1 the BobD, I will let you know of my observations.
BobD - 78 Bus . . . . . . . . .115,063 miles
Chloe - 70 bus . . . . . . . . 219,045 miles
Naranja - 77 Westy . . . . . 185,060 miles
Pluck - 1973 Squareback . . 55,630 miles
Alexus - 91 Lexus LS400 . . 99,705 miles
Chloe - 70 bus . . . . . . . . 219,045 miles
Naranja - 77 Westy . . . . . 185,060 miles
Pluck - 1973 Squareback . . 55,630 miles
Alexus - 91 Lexus LS400 . . 99,705 miles
- midatlanticys
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Very nice! The diagrams are great too. It looks like you could be working on a modern-day Muir book (without the errors ;-)
Suggestion: In one diagram, you show the wear under the wiper path and then changing the wiper path to fix this. I don't think this procedure is mentioned in the text, in the final maybe it should be.
Question: I have an LC-1 hooked up. German Supply Scott suggested a while ago that for fuel economy, it is OK to see 16-17:1 AFR at light cruise (1/3 throttle) and then tune for 13-13.5:1 at > 1/3 throttle. What do you think about that?
Thanks,
Mark
Suggestion: In one diagram, you show the wear under the wiper path and then changing the wiper path to fix this. I don't think this procedure is mentioned in the text, in the final maybe it should be.
Question: I have an LC-1 hooked up. German Supply Scott suggested a while ago that for fuel economy, it is OK to see 16-17:1 AFR at light cruise (1/3 throttle) and then tune for 13-13.5:1 at > 1/3 throttle. What do you think about that?
Thanks,
Mark
- Sluggo
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Added to the "Tech Articles" section.
1977 Bus with Sunroof - "Lucky '77"
2000cc Type IV w/Dual Weber 36s,
Aircooled.net SVDA w/Compufire,
Redline Weber Fuel Pump,
Holley Regulator,
Half Ass Brush & Roller Rustoleum Paint Job,
Incomplete Custom Interior,
Dual Batteries,
Crunched Slider Door.
------------------------------------------------------
- Amskeptic
- IAC "Help Desk"
- Status: Offline
Just above Diagram One:markd89 wrote: Suggestion: In one diagram, you show the wear under the wiper path and then changing the wiper path to fix this. I don't think this procedure is mentioned in the text, in the final maybe it should be.
"While you are here, check to see that the little tiny contact tips on the wiper are landing on good black track through the entire sweep. If you see white plastic showing through, roll the contact strips as per Diagram 1."
Would you like a fuller exposition or perhaps in a different spot?
And now we have a good recent qualifier offered by fusername from theSamba:
there is a cleaner/lubricant spray available at Radio Shack for the wiper board.
The pressure set from the factory of the wiper arm on the track is very specific. The contact area is so small between the wiper and the track that small differences in load will make enourmous pressure differences at tiny little tip of that arm.
For this reason he strongly recommends NOT to touch the wiper arm, and instead to loosen the screws holding the board in place, then simply shift the board and tighten them up again.
There is "lag time" between what the engine is doing and the LM-1's reading of it, so sometimes you may find that it even goes to 20 (there is a throttle switch cut-off of the fuel supply above 1,700 rpm subject to adjustment depending on temp sensor inputs). If you are confident that you have a steady state application of light throttle and the LM-1 reads 16 or 17, that is perfectly acceptable.markd89 wrote: Question: I have an LC-1 hooked up. German Supply Scott suggested a while ago that for fuel economy, it is OK to see 16-17:1 AFR at light cruise (1/3 throttle) and then tune for 13-13.5:1 at > 1/3 throttle. What do you think about that?
Could you give us your model year and engine stats and a hillclimb at 3,500 rpm or so where the engine is unable to increase rpms and let us know what your readings are in that circumstance? Just make sure that the ambient temp is 70, humidity 65-70%, no prevailing wind at an elevation of 400-800 ft, tire pressures are 33/38, GVW 3,700lbs, one driver, 10.374 gallons of fuel onboard, thanx
BobD - 78 Bus . . . . . . . . .115,063 miles
Chloe - 70 bus . . . . . . . . 219,045 miles
Naranja - 77 Westy . . . . . 185,060 miles
Pluck - 1973 Squareback . . 55,630 miles
Alexus - 91 Lexus LS400 . . 99,705 miles
Chloe - 70 bus . . . . . . . . 219,045 miles
Naranja - 77 Westy . . . . . 185,060 miles
Pluck - 1973 Squareback . . 55,630 miles
Alexus - 91 Lexus LS400 . . 99,705 miles
- Gypsie
- rusty aircooled mekanich
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- justgimmecoffee
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very well done, C. Thank you for giving me the tools to keep my bus on the road.
I recently saw a bus with this modification: a hose clamped on the end of the air cleaner inlet with the other end snaked up in the air inlet tunnel. The idea being that it would suck cooler, denser air into the engine during the summer months.
I recently saw a bus with this modification: a hose clamped on the end of the air cleaner inlet with the other end snaked up in the air inlet tunnel. The idea being that it would suck cooler, denser air into the engine during the summer months.
- Amskeptic
- IAC "Help Desk"
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VW provided a hose on the carbureted models, with a bracket above the battery to hang the clamps on. Very nice 38mm paper hose deal right onto the air filter inlet.justgimmecoffee wrote:very well done, C. Thank you for giving me the tools to keep my bus on the road.
I recently saw a bus with this modification: a hose clamped on the end of the air cleaner inlet with the other end snaked up in the air inlet tunnel. The idea being that it would suck cooler, denser air into the engine during the summer months.
The injected buses have absolutely no need for such things. The air intake snorkel is pointed down to the fan area where several billion cubic feet of fresh air are being force fed to the fan not to mention the fan is sucking it down. The air filter is easily getting exactly the same air as was in the air vent, just .00043 seconds later than the modification you speak of.
BobD - 78 Bus . . . . . . . . .115,063 miles
Chloe - 70 bus . . . . . . . . 219,045 miles
Naranja - 77 Westy . . . . . 185,060 miles
Pluck - 1973 Squareback . . 55,630 miles
Alexus - 91 Lexus LS400 . . 99,705 miles
Chloe - 70 bus . . . . . . . . 219,045 miles
Naranja - 77 Westy . . . . . 185,060 miles
Pluck - 1973 Squareback . . 55,630 miles
Alexus - 91 Lexus LS400 . . 99,705 miles
- airkooledchris
- IAC Addict!
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french AFM
on the AFM that is installed in my Vanagon currently, there is a wire that goes from the Static Adjustment arm onto pin #7.
there is also something that connects pins #36 & 6 together with a little electrical doohicky inbetween, as shown here:
it's a little push on connector that just rides right on top of that arm that #7 is connected to.
On the black plastic cap of the existing one it says it was made in france, but has no VW/Audi logo on it.
the german one I have doesn't have that wire on the Static Adjustment arm, nor does it have that wire connecting pins 36&6 together.
the german one has the same part number on the cap as the french one im using now, but the german made one also has the VW/Audi logo on it and VW specific part number.
the Static Adjustment arm on the one installed in the van now cannot be moved, the screw is completely stripped out and cannot be removed.
so, im either going to make this other german one work, or swap over the Static Adjustment arm from the german one over onto the french one.
I tried just running that german one and it didn't like it at all, but it did run. I think that was due to the wiper being too worn, and after the Bentley test it was off when you move the slider around. I moved the track up a bit to get it on the clean and less used portion, then it tested perfectly within spec - though I haven't hooked it back up yet.
am I nuts for even thinking about trying to swap over the hardware, especially with the little differences in those connections shown above?
there is also something that connects pins #36 & 6 together with a little electrical doohicky inbetween, as shown here:
it's a little push on connector that just rides right on top of that arm that #7 is connected to.
On the black plastic cap of the existing one it says it was made in france, but has no VW/Audi logo on it.
the german one I have doesn't have that wire on the Static Adjustment arm, nor does it have that wire connecting pins 36&6 together.
the german one has the same part number on the cap as the french one im using now, but the german made one also has the VW/Audi logo on it and VW specific part number.
the Static Adjustment arm on the one installed in the van now cannot be moved, the screw is completely stripped out and cannot be removed.
so, im either going to make this other german one work, or swap over the Static Adjustment arm from the german one over onto the french one.
I tried just running that german one and it didn't like it at all, but it did run. I think that was due to the wiper being too worn, and after the Bentley test it was off when you move the slider around. I moved the track up a bit to get it on the clean and less used portion, then it tested perfectly within spec - though I haven't hooked it back up yet.
am I nuts for even thinking about trying to swap over the hardware, especially with the little differences in those connections shown above?
1979 California Transporter
- Amskeptic
- IAC "Help Desk"
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IIRC, the resistor is an update to heal Vanagon Syndrome, the "I am pretending to run out of gas" fake out.
Colin
Colin
BobD - 78 Bus . . . . . . . . .115,063 miles
Chloe - 70 bus . . . . . . . . 219,045 miles
Naranja - 77 Westy . . . . . 185,060 miles
Pluck - 1973 Squareback . . 55,630 miles
Alexus - 91 Lexus LS400 . . 99,705 miles
Chloe - 70 bus . . . . . . . . 219,045 miles
Naranja - 77 Westy . . . . . 185,060 miles
Pluck - 1973 Squareback . . 55,630 miles
Alexus - 91 Lexus LS400 . . 99,705 miles
- airkooledchris
- IAC Addict!
- Location: Eureka, California
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wow, that worked wonderfully!loosen the screws holding the board in place, then simply shift the board and tighten them up again.
besides cleaning it up as best as I could, this was the only thing I changed before putting it on the van and it works great. no hesitation throughout the range and it's all within spec according to the Bentley tests.
now I can actually adjust that silver slider, since my french/original one was completely stripped out.
The van doesn't seem to mind that it's missing. This German made one seems to work the same as the French one with the resistor.Amskeptic wrote:IIRC, the resistor is an update to heal Vanagon Syndrome, the "I am pretending to run out of gas" fake out.
On a side note id love to get a larger clearer file from the original post. the images and text are great, but it's a real strain to be able to make out all of the text and fine details. if the originals are larger/clearer id love to see them sometime.
1979 California Transporter
- Gypsie
- rusty aircooled mekanich
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airkooledchris wrote: On a side note id love to get a larger clearer file from the original post. the images and text are great, but it's a real strain to be able to make out all of the text and fine details. if the originals are larger/clearer id love to see them sometime.
Me too. Maybe you could put them in a book...
This loving little jab brought to you by Gypsiecorp. Keeping you in stitches one way or 'tuther since 1966 )
So it all started when I wanted to get better gas mileage....
- Amskeptic
- IAC "Help Desk"
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Maybe you could help me find a proper environment to do the book.Gypsie wrote:airkooledchris wrote: On a side note id love to get a larger clearer file from the original post. the images and text are great, but it's a real strain to be able to make out all of the text and fine details. if the originals are larger/clearer id love to see them sometime.
Me too. Maybe you could put them in a book...
This loving little jab brought to you by Gypsiecorp. Keeping you in stitches one way or 'tuther since 1966 )
I have been unable to.
Colin
BobD - 78 Bus . . . . . . . . .115,063 miles
Chloe - 70 bus . . . . . . . . 219,045 miles
Naranja - 77 Westy . . . . . 185,060 miles
Pluck - 1973 Squareback . . 55,630 miles
Alexus - 91 Lexus LS400 . . 99,705 miles
Chloe - 70 bus . . . . . . . . 219,045 miles
Naranja - 77 Westy . . . . . 185,060 miles
Pluck - 1973 Squareback . . 55,630 miles
Alexus - 91 Lexus LS400 . . 99,705 miles