Guac's ('78 Bus) Power Cutting Out (NOT SOLVED!)

[DurocShark]

1978 Transporter. Stock 2.0 with L-Jet injection and points ignition.

I've had issues that appear to be fuel cutting off every so often. There doesn't seem to be any rhyme or reason to when it starts happening, but a fuel filter replacement usually resolves the issue. For a while.

Cutting open one of the filters shows nothing blocking the filter.

The FPR had a vacuum leak, so it's been replaced.

The only other known bad part is the Aux Air Regulator. No current vacuum leaks that I can identify (I've replaced any cracked hoses, including the ones to the FPR over the past several weeks.)

Here's the best description of the symptoms I can come up with:

Idles fine. Taking off is ok until RPMs hit 3k or so then it's like someone threw a switch. Power gone. It will often stall at that point if I don't feather the throttle for a moment.

I've fixed vacuum leaks. Replaced the entire ignition system (points, condenser, coil, plugs, wires, cap, rotor), as well as cleaned up all the connections to the coil. I've tried it without the tachometer attached. In fact this started before I installed the tach. New fuel pump, FPR, etc.

I'm going to swap in my spare distributor tomorrow night, loaded with Pertronix. I'm also thinking maybe I should replace the fuel lines from the tank again in case they're collapsing. Any other thoughts to try?


EDIT: And a fuel pressure gauge isn't in my future until January. Nobody has a loaner/rental without fittings.

UPDATE:
Interesting development in the symptoms.

1. When the power cuts, the tach goes wacky. Long ago I tried disconnecting the tach to see if it was the cause, with no change.

2. If I drive through it, just suffering the cutouts and bucking, it settles down to something slightly different. The cutouts happen immediately after upshifting and taking my foot off the clutch pedal. Just one buck, sometimes long sometimes short, but still just one buck. Then it runs fine until the next upshift where it does it again.

WTF? Wouldn't it happen mostly at high rpms? Instead of a buck right after shifting? What's with the tach?

UPDATE: NOT FRIGGIN' SOLVED!!!!!!!!!!!!!!!!!!!!!!!!!!!! See below...

[vwlover77]

Possibility: Bad connection of +12V to the coil due to problems in the ignition switch, wiring, or in-line fuse connector feeding the coil.

Another possibility: Bad braided ground wire inside the distributor.

Another: "Dead spot" in the resistor track in the airflow meter.

[DurocShark]

Possibility: Bad connection of +12V to the coil due to problems in the ignition switch, wiring, or in-line fuse connector feeding the coil.

Another possibility: Bad braided ground wire inside the distributor.

Another: "Dead spot" in the resistor track in the airflow meter.

When this first started happening, running a jumper from Battery + to coil + was done with no change.

I'll check the ground in the dizzy. Good thought.

I would think a dead spot on the AFM would happen more frequently?

[Westy78]

I would think a dead spot on the AFM would happen more frequently?

Nope. Don't know if you remember my plight of cutting out/losing power over on TS last year but that ended up being bad resistance on the AFM terminals. The problem would come and go sometimes being fine for a month or more and then all the sudden back to the same ol' thing. Quick and easy to check the resistance on the pins with the multi meter just to rule it out.

[DurocShark]

UPDATE:
Interesting development in the symptoms.

1. When the power cuts, the tach goes wacky. Long ago I tried disconnecting the tach to see if it was the cause, with no change.

2. If I drive through it, just suffering the cutouts and bucking, it settles down to something slightly different. The cutouts happen immediately after upshifting and taking my foot off the clutch pedal. Just one buck, sometimes long sometimes short, but still just one buck. Then it runs fine until the next upshift where it does it again.

WTF? Wouldn't it happen mostly at high rpms? Instead of a buck right after shifting? What's with the tach?

[RSorak 71Westy]

The tach going wacky is telling you the problem is in the ignition system. Look it over good, the primary side.

[DurocShark]

The tach going wacky is telling you the problem is in the ignition system....Look it over good, the primary side.

Everything has been replaced except the plug wires and the distributor. All new coil, points, condensor, plugs.

That tach pegging when this happens is bugging me. I'm thinking about swapping in my spare dist when the snow clears...

[Roadcow]

From your description I'd agree that ignition is the cause, but I feel it's related to your clutch cable. Somehow when you depress the clutch, your ignition system is "seeking ground" through the clutch cable and it's diverting power to the clutch cable (so to speak). I'd first look at your transaxle-to-body braided ground strap. I know it sounds crazy but you said it happens when you have just shifted. It also may be diverting power momentarily from your fuel pump as well. Best wishes for a speedy diagnosis.

[DurocShark]

From your description I'd agree that ignition is the cause, but I feel it's related to your clutch cable. Somehow when you depress the clutch, your ignition system is "seeking ground" through the clutch cable and it's diverting power to the clutch cable (so to speak). I'd first look at your transaxle-to-body braided ground strap. I know it sounds crazy but you said it happens when you have just shifted. It also may be diverting power momentarily from your fuel pump as well. Best wishes for a speedy diagnosis.

Interesting thought. I know the transaxle ground strap is present and appears good, but I've never pulled it off and cleaned it. Sounds like a plan...


BTW: Original Roadcow or new owner?

[Amskeptic]

I know the transaxle ground strap is present and appears good, but I've never pulled it off and cleaned it. Sounds like a plan...

Do it because it is a good thing to do, but it will not have an effect on your symptoms. If that strap could throw the ignition, I guarantee you it would really throw the starter motor.

Be subtle and adventurous in your thinking:
loose wire, pulled by engine movement?
braided strap shorting only when points plate rotates back?
short at wire out of distributor in that plastic plug?
spade terminal inside of distributor shorting against a screw sticking into distributor only when advance unit moves?
Colin

[DurocShark]

Be subtle and adventurous in your thinking:
loose wire, pulled by engine movement?

All redone, rewired, recrimped, reheatshrinked.

braided strap shorting only when points plate rotates back?

That's why I'm going to swap in my spare distributor. The ground strap inside appears good and safe, but...

short at wire out of distributor in that plastic plug?

Checked several times and all that's been replaced.

spade terminal inside of distributor shorting against a screw sticking into distributor only when advance unit moves?
Colin

Possible. I didn't check for that. But swapping distributors again would remove that issue.

I'm hoping this is it. We're getting another foot of snow tomorrow, so may not get anywhere with this for a while. :(

[Roadcow]

I know the transaxle ground strap is present and appears good, but I've never pulled it off and cleaned it. Sounds like a plan...

Do it because it is a good thing to do, but it will not have an effect on your symptoms. If that strap could throw the ignition, I guarantee you it would really throw the starter motor.

Be subtle and adventurous in your thinking:
loose wire, pulled by engine movement?
braided strap shorting only when points plate rotates back?
short at wire out of distributor in that plastic plug?
spade terminal inside of distributor shorting against a screw sticking into distributor only when advance unit moves?
Colin

Not to go against the group master tech but here's a few scenarios where the ground strap could affect the ignition when not affecting starter.
1 Chassis flex or movement when underway (assuming you don't engage the stater while moving).
2. Heat and expansion which will cause a larger gap or poor connection after running for awhile.
I agree that the ground strap is probably not the cause but to say it is not the cause for sure seems a bit inflexible to me.

[Amskeptic]

Not to go against the group master tech but here's a few scenarios where the ground strap could affect the ignition when not affecting starter.
1 Chassis flex or movement when underway (assuming you don't engage the starter while moving).
2. Heat and expansion which will cause a larger gap or poor connection after running for awhile.
I agree that the ground strap is probably not the cause but to say it is not the cause for sure seems a bit inflexible to me.

Sorry. There is *no* way that the ground strap can provide adequate path to starter if it is so poorly connected that it is sensitive to movement. Heat and expansion I really must shoot right down.

We keyboard cowboys can sit back and entertain all kinds of fanciful prognostications, but we really must show a modicum of loyalty to the laws of physics. My list of items above I have had personal experience with. Have you had a loose ground strap that cut out from subtle engine movements or high/low temps but was able to handle the 100 amp starter event but couldn't run the 3 amps of a running engine? Clean question here no attitude and no offense intended.
Colin

[DurocShark]

Actually, I can imagine a situation where that could be plausible. It would have to be some pretty unlikely conditions though...

Bolt just loose enough that when at rest, the strap is resting against the head. But the rocking of the engine and transaxle could have it dancing on the bolt's threads breaking the nice fat ground connection.

Like I said, pretty darn unlikely. And in my case certainly not the issue since I've been driving on packed snow (bouncing all over the place) for the past several days now and not getting any different symptoms. It made for a nice mental exercise anyway.

I won't be able to do any troubleshooting until this weekend at the earliest. With snow coming tomorrow (they're saying another blizzard now), I won't be able to do much.

[Roadcow]

Why yes Colin, actually in my experience I have had a ground strap which appeared to be making good contact, starting the car with a '68 autostick starter. Problem was the engine rubber mounts were broken, that in turn led to the front transmission mount breaking over time (not my bus though). This led to the bus starting but when driven over a bumpy surface the bus would die. Cause, ground strap was severed partially but from outward appearances was fine.
I also only post from experience, but see there can only be one Guru here so will dutifully keep my opinions to myself. No harm intended.