1978 Bus - Idle's But Dies With Throttle

[DurocShark]

A shot in the dark, since I'm still pretty convinced this is an ignition problem:
What is the condition of the plug/coil wires? Ever replaced them since you acquired the Guac?

I replaced them in Feb. (I think? Some time this year). No change in symptoms when I replaced them. (This crap's been going on since Jan.)

I know it's ignition SOMEWHERE. The FI stuff was because there's a tach line to the coil that if grounded would stop the ignition flat, and the ignition stuff has ALL been replaced or swapped.

The lower resistance rotor made no difference when driving.

This is killing me. Having a bus with no go for this long. Arrggghhh!!

[bretski]

You may have mentioned this before, but what happens when the tach is removed from the equation altogether? Same symptoms?

Edit:
Another thought: maybe this is advance-related (since problems show up at higher rpms). Got a spare distributor? Is the ground strap on your current dizzy in good shape and well-connected?

[DurocShark]

Same symptoms, tach, tachless, two tachs.

I have a spare dist. One of the first things I tried, unfortunately. Ground wire looks ok on both. Haven't done any thorough testing though. Tomorrow night I'll take a look.

[soulful66]

Don,
Sorry I haven't responded to this earlier, I am in Iraq and have spotty internet access. Is it possible that the dizzy advance plate is shorting out at a certain rpm? I hear ya on the testing...I was there not so long ago. Sorry I can only provide moral support from here, I would be up there helping you if I could!

Well if I had read your first post more carefully I would have seen you R2 the dizzy. I hope you get GAUC going soon.

Best Regards,
John

[vwlover77]

Good to see a post from soulful66! Be careful over there and godspeed on your return.

Any luck with an AFM swap on the Guac? Did you try that pump volume test yet?

[DurocShark]

Haven't done a volume test. The fact that the pressure is steady through the various issues I've had makes me wonder if the volume could possibly be fluctuating. I would think that the pressure would go down at least a little if there was no volume to maintain the pressure on the rail. Thoughts?

No AFM swap yet. After testing the resistance listed above, I doglegged the wiper and cleaned the track with a pencil eraser. Exactly the same symptoms.

Le sigh.

[vwlover77]

I'm grasping at straws here, but maybe you need to swap out the FI wiring harness with a known good one as a test.

Also, have you carefully checked the in-line fuse holder and fuse in the engine compartment feeding the coil?

Have you hooked up a voltmeter to the + side of the coil while you run the engine to see if power is maintained when the engine dies?

[soulful66]

I'm grasping at straws here, but maybe you need to swap out the FI wiring harness with a known good one as a test.

Also, have you carefully checked the in-line fuse holder and fuse in the engine compartment feeding the coil?

Have you hooked up a voltmeter to the + side of the coil while you run the engine to see if power is maintained when the engine dies?

These are great ideas. I had a thought on the whole fuel volume thing. If there was a clog, like in the fuel rails, the up-stream side of the clog would have good psi and volume while the down-stream side of that clog would cause psi increase and decreased volume. Is this still the same problem you had on your trip to California? I found I had a bad wire once by bending the wire I was testing, it was internally bad. The whole tach thing sounds like a ignition problem, but the 2k rpm cut-out is hard to ignore. Is there any part of the AFM that could short out in relation to the movement of the wiper arm assembly? Maybe not on the top part, but under the wiper that in not readily seen. Don, Have you asked the guy at Blazer's in Denver?
Best Regards,
John

[DurocShark]

Don, Have you asked the guy at Blazer's in Denver?

$$$
:(

The harness is good. I tested it pretty thoroughly. The cutout issue that started this thread was caused by one of the wires being too tight the way it was routed, pulling the connector in the plug away from the pin.

The fuse holder was bypassed with a jumper from battery + to coil +. Several times over the past 8 months or whatever. Never made a difference.

Again, the tach signal is wonky. Fuel has nothing to do with the tach signal.

Here's a video I did several months ago showing it:

http://www.youtube.com/watch?v=vhgbVnLcBFM&feature=user

It's nastier on an analog meter. There is some filtering on the digital that the analog lacks.

[soulful66]

The cutout issue that started this thread was caused by one of the wires being too tight the way it was routed, pulling the connector in the plug away from the pin.

A fine bit of troubleshooting, Don! I agree, fuel has nothing to do with it. Your wiring to the battery has to isolate it from the coil to the ECU. Since you tried a different ECU, is it possible that the problem is in the ECU connector plug itself? It seems that you have already tested and retested everything. I know your frustration, brother. I wish I could drive up there and help with parts or labor to find a solution!
Best Regards,
John

[vwlover77]

OK, here's another shot in the dark - literally.

Get your Bus somewhere nice and dark. I mean, pitch black - no street lights, lampposts, etc.

Pull the rubber sealing boots up on the spark plug wires so you will be able to see down through the tin to the top of the spark plugs.

Let your eyes get accustomed to the dark, and then start the Bus and do your 2000 rpm cutout test. While doing this, look at all the ignition wires from start to end for blue arcing, especially along the path from the coil to the distributor. Some intermittent blue corona "glow" is OK, but if anything is arcing constantly, that's a problem.

I had a cut-out at highway speed issue a long time ago that turned out to be a defective Bosch ignition wire from the coil to the distributor cap.

[DurocShark]

There is no cutout any more.

[vwlover77]

There is no cutout any more.

As in.... Fixed!!!!

Or, as in... it only DIES instead of cuts out?

(Can you post a vid of what it does during the 2K rpm thing?)

[DurocShark]

There is no cutout any more.

As in.... Fixed!!!!

Or, as in... it only DIES instead of cuts out?

(Can you post a vid of what it does during the 2K rpm thing?)

Never made a vid. I'm not breaking the wire connection to film it. :P

Now it's just misfiring/bucking/dying. I posted the whole symptom list on this thread somewhere.

[vwlover77]

I stand by my suggestion to do the "darkroom" test.

Were you able to swap AFMs and try a different one?