Will start but not run... :<

[chitwnvw]

Background.

75 FI Bus. Had been in garage for 1 1/2 years...maybe 2 years. Started bus and it drove out of the garage, parked, shut off engine, when I tried to start it again it would start and then die out after a few seconds. Tried adding some fresh gas, seemed that things got better, ran a little longer, added some more fresh gas, ran even longer, even more gas and not so good, would turn over and run for a few seconds and then die.

Drained all gas, added a few new gallons, would start and die after a few seconds. Checked for vac leaks, none found. Checked plugs, pretty fouled, changed to new plugs, still the same, starts, runs a few seconds and then dies.

So I need some help thinking this through, seems like the cold start valve is spraying, there is a spark and it runs for a few seconds, then it runs out of gas. The gas pedal seems to have no affect on the results...

[ruckman101]

Clean fuel filter? Crud in the tank? Fuel pump?


neal

[Lanval]

Clean fuel filter? Crud in the tank? Fuel pump?


neal

I agree, though I'd go in this order:
1. Clean fuel filter (this is preventive medicine, and should be done if the current filter is old, whether the car is running or not)
2. Fuel pump - verify that it's putting out fuel. The easiest way would be listen for the pump running when turn the key; you can also verify fuel pressure at the engine
3. Crud in the tank - this is kind of hard to check, and expensive/time consuming to fix, so it's the last on the list. Colin suggested I remove my tank, and roll some ball bearings around in it to get the loose, flaky stuff free. I don't remember what he said to use as liquid to hold/drain the flakes. Check with Colin.

Mike

[Amskeptic]

Colin suggested I remove my tank, and roll some ball bearings around in it to get the loose, flaky stuff free. I don't remember what he said to use as liquid to hold/drain the flakes.

Gas makes a good solvent.

Chitwnvw, it sounds like your pump worked for a little while then clogged with varnish.
Remove a fuel hose and stick in a container, turn on ignition and move the wiper under the black cap of the AFM to turn on the pump. Listen for the relay to click. If gas does not come out immediately, stop the test. The pump can overheat and die quickly on a stall.
If clogged/stalled, remove pump. Carb cleaner the in and the out, and swish. Then do a carb cleaner shot plus reverse leads to a 12vt battery to run the pump backwards briefly. Then run it forward. Then rinse with gas and install and try again. If it never runs, replace.
Colin

[Kubelwagen]

Getting ready to do a similar test - is there a way to assess if the volume the pump is producing is adequate in this procedure? Or is any gas considered enough?

[soulful66]

My '79 did the same thing. The cause on mine was a rotted (1 yr old) Aux Air elbow.

Regards,
John

[chitwnvw]

So tonight I checked the fuel flow and with the key on and the fuel line in my gas can, flicked the wiper on the AFM and ran it for 30 seconds or so and it seemed to be coming out with plenty of gusto. I'd brought my fuel pressure gauge but forgot to pack a 7mm wrench so I couldn't measure the pressure.

Replaced the aux air elbow, it looked suspect and I had been monkeying with it. No change.

Checked out aar, it was wide open at cold.

For kicks, I replaced double relay, checked out a fuel injector and replaced the hose, the strange U hose on the decel valve. Now it runs for 15-30 seconds, but accelerator pedal still has no affect on the rpms.

Shot some pictures:



This is an 'extra' FI electrical hook up. It is blue, the ones hooking up to the injectors are brown, the one hooked to the cold start valve is blue also. I have no clue what this is meant to hook up to.( this is the 3/4 side )



The FI hook ups to the 3/4 side...



The spaghetti that is the electrical layout in the engine compartment...

[Amskeptic]

accelerator pedal still has no affect on the rpms.

That is so usually the AFM plug. Check that each wire terminal is properly seated in the plastic plug.
When you insert the plug into the AFM, check that each wire stays in place and does not push back into the harness. You can see this by peeling back the rubber boot over the plug and getting a visual on each wire. If known good connection still yields no accelerator effect on engine, harness itself should be checked for continuity all the way to the ECU.
Colin
(accelerator cable is hooked up securely to the throttle lever, right?)

[Randy in Maine]

Could you humor me and examine that S boot in the bright Chicago sunshine to see if it is split open on one of the pleats?

Does this thing have a funky injector style electrical connection at the decel or EGR valve? I think somebody has the that set up, but I never have so I don't know.

[poptop tom]

Is the "extra" plug for the thermo-time switch?

[deschutestrout]

Todd, isn't this what Trout did when we were struggling to get her running? And...we swapped AFM and all was well...we were suspicious the AFM plug in wasn't seated properly. Colin's post made me think of our Trout issue. Good luck! Let us all know what it was!!!

[chitwnvw]

Hmmm, I tried a different sort of troubleshooting exercise, instead of pulling one spark plug wire at a time and seeing if there was any difference, I pulled all of them and plugged in only one at a time. Turns out 3 and 4 are not firing at all, 1 is firing a bit, and 2 is the only one firing decently at all.

Any ideas on how this could be happening? Seems kind of weird to think of the distributor cap or plug wires to take a dive so instantaneously.

Weird side note, the AFM has only 6 wires in the plug instead of the 7 that every other one I've seen has, is this a '75 thing?

[Amskeptic]

Hmmm, I tried a different sort of troubleshooting exercise, instead of pulling one spark plug wire at a time and seeing if there was any difference, I pulled all of them and plugged in only one at a time. Turns out 3 and 4 are not firing at all, 1 is firing a bit, and 2 is the only one firing decently at all.

Any ideas on how this could be happening? Seems kind of weird to think of the distributor cap or plug wires to take a dive so instantaneously.

Weird side note, the AFM has only 6 wires in the plug instead of the 7 that every other one I've seen has, is this a '75 thing?

Read your Bentley. 6 wire is early, as is the electrical egr plug.
Do not do the one cylinder-at-a-time test. It is hell on the mechanicals.
I do not think that tells you anything significant, as having only a single plug firing can mess up the coil's signal to the ECU.
Colin

[chitwnvw]

Anyone know what this is:



Between the plenum and the #3 plug?

[Amskeptic]

Anyone know what this is:
Between the plenum and the #3 plug?

Help us out.
Is that a vacuum hose? Does it attach to a nipple?
Colin