2-for-1 and possibly related: Bucking and unstable/nonidle

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Ronin10
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2-for-1 and possibly related: Bucking and unstable/nonidle

Post by Ronin10 » Fri Dec 12, 2014 8:53 pm

Need help diagnosing two possibly related issues...

When Colin visited me this summer, we accomplished a lot, but one of the things we didn't have time to sort out while doing some AFM tuning was what he termed a "nervous idle." It will run fine through the RPM range with the exception of anything below about 1500 RPMs.

Well, since then, I've been periodically trying to address this crummy idle as well as the re-emergence of my bucking issue. I suspect they are related.

To address the bucking issue, I tried narrowing things down and have done the following (in no particular order):
  • Adjusted my valves (several times...best seemed to be to adjust them warm at contact plus 1/2 turn)
    I rebuilt my distributor
    I removed my electronic ignition and installed points
    I gapped my plugs
    I actually went and purchased and installed one-by-one, a new coil, cap, rotor, and wires (needed a set of spares anyway)
    My tired old battery crapped out so I purchased a new one along the way
    Replace my fuel filter (and bought a spare)
    Timed my engine to 30* BTDC (hoses off)
    Searched and searched for vacuum leaks, but didn't find any
When Colin was here, we tuned the AFM via his senses, but mine aren't that well attuned so I dug out my LM-2 this past weekend and tuned the AFM using that as a guide. Here's my AFRs and fuel pressures at the same RPM (I am wondering about the health of my fuel pump):
  • <1500 rpm: LM-2 puts out nonsensical high AFRs, engine won't idle, fuel pressures 38-40 psi.
    1500 rpm: lowest level that engine is smooth, AFR=14.8, fuel pressure=32 psi
    2000 rpm: AFR = 14.7, fuel pressure = 30 psi
    2200=2400 rmp: anytime I go through this range, there is a higher pitch vibration sound.
    2500 rpm: AFR=14.7, fuel pressure = 30 psi
    3000 rpm: AFR = 14.5, fuel pressure = 30 psi
    3500 rpm: AFR = 15.0, fuel pressure = 30 psi
Other observations...my son and I took the bus for a test drive with the fuel pressure gauge connected. It never got any lower than 29psi and when running well, it was typically 34-36 psi. When the idle would fall apart or die, it would rise to 39-40 psi. Once it died, the fuel pressure would recover to 32 psi. What else? The bucking only occurs under load...out of gear, in the garage, I can run the rpm up (as long as I start past 1500) through 4000 rpms without any evidence of issues. Also, I did see another reference that the CA decel valve can really screw up idle. I'm not sure if mine is CA spec, but the part number is 022 133 551B.

The last possibility I can think of that might be wrong with the system is that my FI harness is in a deplorable, but seemingly functional state, the RPM input wire being the worst condition. I want to get a new one, but $400 and 5 weeks starting Jan 12 is quite a ways off and out of my expense availability at the moment. I can get a used one from Avery's for $175, but that's used (and substantially more than the ones I've seen on the Samba classifieds) which comes with it's own question marks and no guarantee it'll work. What's more, my bus is a late 76 model so it has 7 pin AFM connection, mechanical EGR, and a full throttle microswitch.

Running out of ideas here. Any suggestions?
Oscar: 1976 Sage Green Bus, Stock Motor, Solid Lifters, Manual Transaxle

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Ronin10
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Ronin10 » Fri Dec 12, 2014 9:59 pm

Some other thoughts that occurred to me after posting...the bucking seems to come in fits l. It'll get horrendous-undriveable-but sometimes I can finesse my way through it. Other times it's so bad , I need to get out of traffic asap.

My AAR hose collapses at high RPM but doesn't seem to afffect things.

I think that's ut. I may have overlooked some other thing, but that is all i can think of at the moment.
Oscar: 1976 Sage Green Bus, Stock Motor, Solid Lifters, Manual Transaxle

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Amskeptic
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Amskeptic » Sat Dec 13, 2014 6:11 am

Ronin10 wrote:Some other thoughts that occurred to me after posting...the bucking seems to come in fits l. It'll get horrendous-undriveable-but sometimes I can finesse my way through it. Other times it's so bad , I need to get out of traffic asap.

My AAR hose collapses at high RPM but doesn't seem to afffect things.

I think that's ut. I may have overlooked some other thing, but that is all i can think of at the moment.
Below 1,500 rpm, your fuel pressure is going up because available vacuum is going down. I am sensing a vacuum leak, perhaps in the s-boot pleats? brake booster line? (you can cap it off and look for improvement).

If someone can start the engine for you, can you get a good idle under 1,500 rpm by gently nudging wiper counter-clockwise a little bit?
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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wcfvw69
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by wcfvw69 » Sat Dec 13, 2014 7:08 am

http://www.thesamba.com/vw/forum/viewto ... highlight=

I remembered this thread on The Samba.
1970 Westfalia bus. Stock 1776 dual port type 1 engine. Restored German Solex 34-3. Restored 205Q distributor, restored to factory appearance engine.

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Ronin10
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Ronin10 » Sat Dec 13, 2014 10:24 am

the smoker is a good idea. I'll try cobbling one together this weeekend to verify I have no leaks.
Oscar: 1976 Sage Green Bus, Stock Motor, Solid Lifters, Manual Transaxle

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Ronin10
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Ronin10 » Sat Dec 13, 2014 1:49 pm

Okay, spent a few hours trying to rig up a smoker. I first tried adapting a Halloween fog machine, but that didn't really work. I think that stuff is more liquid vapor than smoke so it didn't seem to travel far into the engine before condensing out. I then went the route of an actual "smoker," using incense instead of a cigar or something similar. It smelled very nice.

What I found was that the AFM itself seems to have a leak. It struck me as a very unusual location so I assumed was coming from somewhere underneath the AFM. I had a helper manage the smoker while I scanned underneath the AFM, but the smoke clearly originated from above at the AFM. I tried putting the cover back on the AFM and holding it tight in position, but the smoke still escaped under one of the corners of the AFM cover.

I don't know the internal construction of these devices beyond what I can see under the cover and peering through either end of the airflow channel, but I'm guessing there's some kind of seal (simply grease perhaps?) around the top of the pivot shaft for the wiper and that has decayed sufficiently to allow some air to be drawn in through the circuit board area. Siliconing the cover in place should fix that, but I'd like to be certain that is going to fix the problem so that I'm not carving off the cover again, sealing it, cutting it off, etc.

I also do have another AFM which I could put in place and try to tune. Maybe I'll give that a go. I didn't see smoke coming from anywhere else. Thoughts?
Oscar: 1976 Sage Green Bus, Stock Motor, Solid Lifters, Manual Transaxle

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Amskeptic
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Amskeptic » Sun Dec 14, 2014 6:57 am

Ronin10 wrote:Okay, spent a few hours trying to rig up a smoker. I first tried adapting a Halloween fog machine, but that didn't really work. I think that stuff is more liquid vapor than smoke so it didn't seem to travel far into the engine before condensing out. I then went the route of an actual "smoker," using incense instead of a cigar or something similar. It smelled very nice.

What I found was that the AFM itself seems to have a leak. It struck me as a very unusual location so I assumed was coming from somewhere underneath the AFM. I had a helper manage the smoker while I scanned underneath the AFM, but the smoke clearly originated from above at the AFM. I tried putting the cover back on the AFM and holding it tight in position, but the smoke still escaped under one of the corners of the AFM cover.

I don't know the internal construction of these devices beyond what I can see under the cover and peering through either end of the airflow channel, but I'm guessing there's some kind of seal (simply grease perhaps?) around the top of the pivot shaft for the wiper and that has decayed sufficiently to allow some air to be drawn in through the circuit board area. Siliconing the cover in place should fix that, but I'd like to be certain that is going to fix the problem so that I'm not carving off the cover again, sealing it, cutting it off, etc.

I also do have another AFM which I could put in place and try to tune. Maybe I'll give that a go. I didn't see smoke coming from anywhere else. Thoughts?
Ignore . . . that ain't it. Substituting with an another AFM is not a bad idea, however, for variable reduction.
The "let someone else start it and you nudge the wiper rich at idle" idea is a good one for narrowing down the search.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Ronin10
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Ronin10 » Sun Dec 14, 2014 12:37 pm

I'll hold off on the AFM for the time being. If that's not the issue, I'd actually like to hold that fixed so that later, I can maybe setup my other AFM as a spare and be able to distinguish the effect of a leaking AFM in isolation. Plus, time is at a premium, I'd rather focus on things that will bear fruit to the issue at hand.

I'm not able to really execute an idle. Anything below 1500 rpms in unstable so the wiper arm is dancing all over the place. There's no nudging it any direction at that point as it won't sit still long enough to do so. What is achievable is to possibly hold the wiper in place, at an average position and "nudge" from there. I'm not sure though if doing so would provide reliable information though since the engine is artificially held to an external condition.

Updates...I don't know if Colin will recall this, but my old distributor was clocked 90* off. I fixed that yesterday afternoon, but as you'd expect, I noticed no change after a brief test drive, but I wanted to document the difference. At least it looks right now.

Going forward today, I'm going to play with the mixture and idle screws some more today to see if I can improve the idle any. As soon as I get off of idle (1500+), the operation of the engine-bucking aside-is great so by limiting myself to these two adjustments, maybe I can see the problem with fresh eyes enough to get the idle stable enough to where the engine won't die everytime I come to a stop.
Oscar: 1976 Sage Green Bus, Stock Motor, Solid Lifters, Manual Transaxle

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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by asiab3 » Mon Dec 15, 2014 12:15 am

I'm curious if holding the wiper in one place stabilizes the idle. Get the engine going over 2k RPM, then gradually slow down, then watch where the wiper "should" land at a normal idle. See how close you can hold the wiper to there and achieve a steady RPM. Could you then adjust the idle mixture screw to compensate for the (probably rich) AFM wiper "placement"? I'd be looking for worn wiper tracks doing this, which would provide erratic readings in resistance. A consistent reading from the AFM that jives with the ratio of air and fuel could yield a steady idle.

Does this make sense? Or is it diagnostically useless?
Robbie
1969 bus, "Buddy."
145k miles with me.
322k miles on Earth.

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Ronin10
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Ronin10 » Mon Dec 15, 2014 6:01 pm

My helper (my son) keeps getting called into work so I haven't been able to test a fixed position wiper. I have done that previously, but I can't recall what happened. Anyway, here are some observations from my drive to/from work today which hopefully, will give more insight into my dilemma...
  • In the morning, I can pretty much always count on a bucking fit as I travel along Maple Valley Hwy. I let the bus warm up for several minutes and start out on my drive. The bucking occurs about 4-6 miles from home, flat then down a big hill, then flat again which is where the bucking fit occurs.

    Since correcting the position of the distributor and retiming to 28* (instead of 28-30), the bus seems to drive better when it's not having a fit, but the I seem to experience more misfires, though minor.

    On the way home, I had a bit of a bucking fit, but it was minor until I got home. I came to a stoplight outside my neighborhood and when I went accelerate, the bus just kind of fell on its face, not giving me much of anything, regardless of throttle position. I managed it over to the side of the road where it died and didn't want to restart, kind of like it was flooded. It eventually restart, but with buck fit and a surge of acceleration which was too strong for the throttle I had been giving it. I thought someone had strapped a JATO tube to my bus while stopped at the light.

    Also, I found since adjusting the distributor, that I can massage the rpms down to about 1000-1200 before they break up.
I wonder if my oversized valves combined with a slightly longer duration camshaft are pushing the limits of how L-Jet manages idle. Hope to tackle the mixture and idle screw experiment along with Robbie's suggest on manually holding the wiper arm, but doesn't seem like it'll happen tonight.
Oscar: 1976 Sage Green Bus, Stock Motor, Solid Lifters, Manual Transaxle

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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by satchmo » Mon Dec 15, 2014 7:17 pm

Bucking while in motion and not at rest = bad electrical contacts. For me, it was a connector in the double relay/resistor block. So check every connection there to make sure you have good contact. Same with the AFM plug and wire harness.

If all is rosy at the connections, it could be the wiring harness itself. A lot can happen to 40 year old wiring that is subjected to thousands of hot/cold cycles. You have pretty much eliminated everything else.

Tim
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First, by reflection, which is noblest;
second, by immitation, which is easiest;
and third, by experience, which is bitterest. -Confucius

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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by SlowLane » Mon Dec 15, 2014 11:34 pm

Okay, I'm going to put out what is probably the most ridiculous suggestion, and please don't feel that I'm trying to insult your intelligence, but:
Is it possible that your fuel pressure regulator is getting its vacuum signal teed from the ported vacuum used for the distributor vacuum advance, instead of the plenum vacuum? The high fuel pressure at low RPMs are rather suspicious and would be in line with that scenario.

Oh wait, I just saw your mention of larger valves and longer duration cam (presumably with high overlap). That could certainly throw a wrench into things at idle.

The Vanagon CA-spec decel valve that I measured opened at about 17" of vacuum, whereas the Federal spec valve opened at about 22", so there's definitely a difference there. Measure it with a Mity-Vac so you know for sure, but I'd suggest doing your troubleshooting with the decel valve disabled, just to eliminate that variable.
'81 Canadian Westfalia (2.0L, manual), now Californiated

"They say a little knowledge is a dangerous thing, but it is not one half so bad as a lot of ignorance."
- Terry Pratchett

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Ronin10
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Ronin10 » Tue Dec 16, 2014 8:10 am

Thanks for the suggestion SlowLane. No worries about insulting my intelligence. I'm at the point where I'm second guessing everything...

That said, I'm pretty confident in my vacuum line configuration. When I purchased the bus a few years back, the vacuum system was wildly cobbled together. It ran, but didn't match any references I could find and the air cleaner itself wasn't hooked up. It's since been straightened out: fuel pressure regulator is teed into the decel valve and plenum and the distributor is teed into the throttle body and air filter housing. Unless the late-76 buses had a special vacuum line configuration, I followed Ratwell's guide.

I've been wanting a vacuum gauge for a while, but it was never a huge priority when I had the money.

On the harness front, I am deeply concerned about the state of my harness and have a bias that it may be a contributor to the bucking, if not the idle as satchmo suggests. When I had the engine out this summer, I expressly made a point of cleaning the grounds underneath the plenum. The other connectors all seem in good order and functional, but there is some cracked sheathing and coil wire lead is fraying (which seems the most likely culprit).

I have been looking around for a replacement harness now for over a year, but the late-76 buses are 1/2 year only harness (7-pin AFM, mechanical EGR, 2 wire lead to full throttle switch) and hard to come by. Kyle Industries, while highly regarded for his work, is about $400 and he can't start on a replacement until January 12 with a delivery date up to 5 weeks later. Avery's has a used one for $175. After this week, I'm off until January 5 so I may make the drive down to check it out. Otherwise, I have almost all the parts I need to rebuild one of the spare harnesses I have sitting in my garage, but they've been salvaged from other model years and I'd need to figure out how to correctly incorporate the full throttle microswitch into it with removing the one from my bus (it's a daily driver).

Long story short, the harness is on the To Do list, I just want to make sure I've eliminated everything else.
Oscar: 1976 Sage Green Bus, Stock Motor, Solid Lifters, Manual Transaxle

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Amskeptic
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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by Amskeptic » Tue Dec 16, 2014 9:13 am

Did you say that the wiper was dancing around too much to play with it below 1,500 rpm?

That is so wrong. It should smooth. If it is fluttering, we have a problem. Do you have a recent valve adjustment/compression test result to share?

An aggressive cam will fake out an AFM a little bit, but by your description, you can't get a handle on the wiper to hold it and run it from lean-to-rich-to-lean to see if you can improve this refusal to idle?
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

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Re: 2-for-1 and possibly related: Bucking and unstable/nonid

Post by airkooledchris » Tue Dec 16, 2014 10:52 am

id swap in the spare AFM just to compare the results and quickly and easily cross that off your list as a possibility (if the behavior stays the same afterward.)
1979 California Transporter

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