Return of bucking. A jinx and a curse? Solved!

[Gypsie]

Swapping the parts can happen in place without removing the dizzy. There are a few fine motor skill steps though and a tiny screw that can get all elusive and reluctant so I might suggest a pull of the dizzy for this step.

You can remove the dizzy by removing the nut for the hold down clamp (that way it stays timed to your last setting). You will want to re-time anyway but with a start point your in a better position. With it out and on the bench you can get familiar with your parts...(uh, don't forget to bring flowers and hold the door...).


The bottom of the dizzy has an offset slot that slips down into an offset groove on the drive gear (down in the hole). Just make a mental note where the rotor is pointing when you pull it and start it there when you go to put it back in. No need for TDC figgerin'. I recommend a new dizzy o-ring if the old on has been there for a while. The removal/replacement process is not kind to old material.

I personally would swap the parts out in place using the utmost care and a grasping screwdriver (for the tiny screw). Quick and clean like. Take care if you go this route.

2cents.
(I think this is a path worth following BTW)

[luftvagon]

I love this thread, but I hate the fact you are having issues. Hopefully you don't end up hating your bus, because of the issues. On the other hand, you need to go through all this because it builds character... No one else can support these machines better than your own-self. Once all this is behind you, and should you experience similar issues in the future, you will be able to fix them yourself. Now back onto the issue. I know its frustrating not to be able to drive it back home.

[aopisa]

Thanks. I may not hate my bus (yet), but I am extremely disappointed in it.

I have no choice but to be the only person to work on it. I am the only person I know around here who has a bus. There are no mentors, old hippies, Lucky Lab type gatherings, etc. where I can receive help. It's me, this forum and Colin for 9 hours once a year.

Now onto the problem.

I put in the NOS distributor, new condenser and points. I was barely able to get the timing set before the engine started hesitating, bucking, missing whatever you want to call it.

So, I am going to call AAA for a tow home.

Can I have it towed by a regular tow truck about 5 miles or do I need a flatbed?

[luftvagon]

You can tow it either way, as long as you have a manual. Usually what they will try to do is lift it by the drive wheels (rear-wheels), but if they can't. They can tow it using the front wheels, as long as you have it in Neutral, it will be ok.

Someone may pitch in here, and scream about being towed by the front wheels...

[Lanval]

Yeah, the Bentley is not a repair/work guide, really. And it's sometimes (very) wrong.

Take a breather and remember these systems are essentially simple. Engine needs:

Air
Fire
Gas

That's it. It's not getting one of those in the right way/amount. Each of those individual systems has a start and end point. End point is in the engine, and the start point is somewhere else. You may need to eliminate each system in a step-by-step way. Start with fire, for example. Go from the battery/ignition forward to the spark plugs step by step. If each step is correctly valued/working, then you've eliminated it.

Then Air. Then Gas. You'll find it. It's a mechanical system, it IS there. Just being sneaky.

I still haven't heard about what you're doing to make it buck. Sounds like you go it to buck hesitate today while not driving it. Was it only with the throttle open? Will it idle? Does it run fine for the first 5 minutes then die? These are important clues.

ML

[Randy in Maine]

My rule of thumb is to only remove the distributor when I am at TDC getting ready for #1 to fire. That way I know where it came from when it goes back in.

See if those plugs are fouled also. It does not take long for that to happen.

If you were closer, you could borrow my tow bar. That was money well spent just to have (although I have only used it once to pull my bus, it has pulled many buses for many miles).

[aopisa]

Thanks, if you were closer I would be asking you to come over and take a look.

The local AAA guy just called and said, "Again!?" He's going to tow me tomorrow.

[aopisa]

Yeah, the Bentley is not a repair/work guide, really. And it's sometimes (very) wrong.

Take a breather and remember these systems are essentially simple. Engine needs:

Air
Fire
Gas

That's it. It's not getting one of those in the right way/amount. Each of those individual systems has a start and end point. End point is in the engine, and the start point is somewhere else. You may need to eliminate each system in a step-by-step way. Start with fire, for example. Go from the battery/ignition forward to the spark plugs step by step. If each step is correctly valued/working, then you've eliminated it.

Then Air. Then Gas. You'll find it. It's a mechanical system, it IS there. Just being sneaky.

I still haven't heard about what you're doing to make it buck. Sounds like you go it to buck hesitate today while not driving it. Was it only with the throttle open? Will it idle? Does it run fine for the first 5 minutes then die? These are important clues.

ML

Yes, Now it bucks, hesitates, lurches, whatever you want to call it only after running a minute or two. It does not do it while idling, only when the throttle is applied. It used to be very intermittent, now it is constant. I suppose this is good since it might make it easier to track down.

As I stated, I was barely able to get it timed correctly. It wasn't long before I could not get it to hold at a steady constant throttle speed.

I cannot make it down the road more than a few feet before the problem occurs and with it the resulting loss of power.

[luftvagon]

At this point; it sounds like TSII; that is, if you have a window of 2-3 minutes of driving, before it goes crazy. It could also be a bad ground, as with heat, wire resistance increases...

[Lanval]

It does not do it while idling, only when the throttle is applied.

You are home. Doesn't buck for 2-3 minutes, then only under load. Very few issues in play, and easy to check. I assume it will idle happily while you check different things? If so, time to find out what's not doing it's job under load.

ML

[SlowLane]

Y'know, pretty much all of the investigation and advice seems to be focussing on electrical and spark issues, but we've largely ignored the possibility of a "false air" problem that we all know L-Jet is sensitive to.

Because L-Jet relies so heavily on the signal from the AFM as its primary sensor, any source of air that bypasses the AFM is "unmeasured" air, which means that the ECU can't account for it in its fuel timing calculations. There are a number of avenues that can introduce unmeasured air, not all of them obvious. Leaky valve cover gaskets, for instance, or a poorly-fitting oil cap. These tend to be minor, however.

Just looking at your pictures, I can see a couple of potential candidates: the EGR system and the large vacuum tee feeding the brake booster/decel valve. The vacuum tee looks a little tired from the picture, especially where the transparent decel valve hose plugs into it.

I suspect the EGR system because of your present symptom of having a good idle, but everything going to hell when you open the throttle. If you have a functioning EGR system (it isn't clear from your pictures if you do, but you do have the EGR pipe, which is presumaby bolted to an EGR valve, which in turn is bolted to the side of the air plenum}, then the EGR valve gets opened by a pushrod attached to the throttle linkage. This allows a metered amount of exhaust gas into the intake. The exhaust gas metering is accomplished with a small orifice in a special gasket that goes between the pipe and the valve. If that orifice gets larger for any reason, then more exhaust gas than needed will be introduced into the intake, Or if the EGR system is compromised, it might be introducing outside air instead of oxygen-depleted exhaust gas.

It's pretty easy to check this hypothesis: simply disconnect the EGR pushrod from the throttle linkage temporarily so that the EGR remains closed under all conditions (it would be a good idea to check and make sure that the valve does remained closed by itself. There is a spring that is supposed to keep pressure on the valve to keep it closed). With the valve linkage disconnected, open the throttle and see if it still stumbles.

FWIW, running with the EGR disconnected won't harm the engine. It's probably a safe bet to say that the majority of busses on the road today are running around with disabled EGR systems.

[56ovalbug]

Looking back at you engine pics the two fuel evaporating lines are joined together and there's no T going to the canister on the fire wall. If your fuel tank is air tight this may be the cause of your problems - It needs venting and more so on hot days. When loosening the gas cap do you hear air/fuel vapor escaping?

[aopisa]

Y'know, pretty much all of the investigation and advice seems to be focussing on electrical and spark issues, but we've largely ignored the possibility of a "false air" problem that we all know L-Jet is sensitive to.

Because L-Jet relies so heavily on the signal from the AFM as its primary sensor, any source of air that bypasses the AFM is "unmeasured" air, which means that the ECU can't account for it in its fuel timing calculations. There are a number of avenues that can introduce unmeasured air, not all of them obvious. Leaky valve cover gaskets, for instance, or a poorly-fitting oil cap. These tend to be minor, however.

Just looking at your pictures, I can see a couple of potential candidates: the EGR system and the large vacuum tee feeding the brake booster/decel valve. The vacuum tee looks a little tired from the picture, especially where the transparent decel valve hose plugs into it.

I suspect the EGR system because of your present symptom of having a good idle, but everything going to hell when you open the throttle. If you have a functioning EGR system (it isn't clear from your pictures if you do, but you do have the EGR pipe, which is presumaby bolted to an EGR valve, which in turn is bolted to the side of the air plenum}, then the EGR valve gets opened by a pushrod attached to the throttle linkage. This allows a metered amount of exhaust gas into the intake. The exhaust gas metering is accomplished with a small orifice in a special gasket that goes between the pipe and the valve. If that orifice gets larger for any reason, then more exhaust gas than needed will be introduced into the intake, Or if the EGR system is compromised, it might be introducing outside air instead of oxygen-depleted exhaust gas.

It's pretty easy to check this hypothesis: simply disconnect the EGR pushrod from the throttle linkage temporarily so that the EGR remains closed under all conditions (it would be a good idea to check and make sure that the valve does remained closed by itself. There is a spring that is supposed to keep pressure on the valve to keep it closed). With the valve linkage disconnected, open the throttle and see if it still stumbles.

FWIW, running with the EGR disconnected won't harm the engine. It's probably a safe bet to say that the majority of busses on the road today are running around with disabled EGR systems.

Finally got it home. I was able to drive it around a little while I was waiting for the tow and you guessed it, no bucking or hesitation. SInce luck has not been in my favor lately with this bus, I decided to have it towed anyway. If it conked out on a narrow country road or worse a hill, it would have been more of a pain to get it on the flatbed.



The EGR system is blocked off at the plenum. Colin fashioned a gasket out of something he found in my garage and sealed it off in place.

I do agree that the vacuum tee around the decel valve looks tired. I was checking that out yesterday along with the AAR elbow and hoses. The AAR elbow has some visible cracks on the outer surface, but is internally intact. I plugged one end and blew into it and it held. I did find some cracks in the S boot last year which I patched with black RTV. It seems fine and I have checked for vacuum leaks several times. Still not ruling anything out as I could have missed something.

Looking back at you engine pics the two fuel evaporating lines are joined together and there's no T going to the canister on the fire wall. If your fuel tank is air tight this may be the cause of your problems - It needs venting and more so on hot days. When loosening the gas cap do you hear air/fuel vapor escaping?

I do not experience this when removing the gas cap. I will however look at those lines.

Thanks.

[SlowLane]

The EGR system is blocked off at the plenum. Colin fashioned a gasket out of something he found in my garage and sealed it off in place.

Ok. Note that the actuating bit of the EGR valve actually protrudes a bit from the body of the valve, so it's possible that it might have gradually poked a hole into the Colin-fabbed gasket-out-of-something-found-in-the-garage.

I do agree that the vacuum tee around the decel valve looks tired.

Airhead Parts sells a reproduction vacuum tee if you find that you need one.

[luftvagon]

If there are any vacuum leaks, past the throttle body, you would know. The idle would be "hunting", as the engine would rev up and then slow down.

How full/empty is your gas tank?
Did any air escape when you opened the gas cap?
Do re-check for vacuum leaks.
Do re-check the grounds. Do me a favour; run a line directly to (-) side of the battery. Hook it to an ohm meter, and measure resistance at every ECU ground point.
Do re-check the TSII.

What you got?
:popcorn