73-87 Chevy _ GMC Trucks > Engine/Drivetrain

That infernal stalling problem again . . .

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haroldwca:
As I've researched this problem on the internet, it seems as everyone with a carburetor has a stalling problem that mimics a vapor lock.  I drive an '85 2WD Silverado with a '92 TBI 350 long block, '79 Quadrajet, and original '85 intake manifold and exhaust manifolds.  I doubt that it makes any difference, but the transmission is the original 700R4.  My symptoms are as follows.  Short trips around town or any driving during cooler weather (below 70 degrees) works fine.  Once the mercury rises into the high 70s or above, the condition rears its ugly head.  I drive for 10-15 minutes or more, then shut off the engine.  If I re-start immediately, there is no problem.  If I wait for more than five minutes and then re-start, the engine will stall within the first 1000 feet.  I can usually re-start once, but the stalling will recur in a similar manner.  It will not re-start. 

After suspecting the fuel line location (stock, behind alternator), I ran a rubber hose from the fuel pump, routing it away from the engine toward the A/C housing, then back to the carb, maintaining as much distance from the exhaust manifold as possible.  The last time it stalled, I pulled the hose from the fuel pump, cranked the engine, and no fuel came from the pump.  I poured gasoline into the open fuel line, started the engine, and maintained a fuel flow to the carb (using a soft drink bottle).  The fuel pump eventually began pumping fuel again.  I re-attached the fuel hose to the pump and drove away.

The above experiment seems to eliminate the carburetor.

Here is what I have done so far.

(1)  Dropped the fuel tank to examine it internally.  Tank was pristine (and likely original).  Fuel pickup was in good condition.
(2)  Replaced all rubber hoses in fuel system from tank pickup to carburetor.  Not pristine, and also likely original.  I also blew out the hard lines with my compressor.  No blockages seemed present.
(3)  Replaced fuel pump a couple of times since stalling has been occurring.  No difference.
(4)  Removed catalytic converter for another reason altogether.  Not suspected, but I thought I would mention it.
(5)  Replaced fuel cap because I thought it might not be venting probably.  I don't like to just throw parts at a problem, but it was cheap enough.
(6)  I have rebuilt the carburetor, starting with a thorough cleaning in solution, then replacing needle, seat, float, gaskets, accelerator pump, etc.  I also re-epoxied the primary and secondary metering wells.  I have properly adjusted the idle mixture screws, float, and choke.  Starts with one pump of the pedal first thing in the morning.  It runs great . . . until it doesn't.

I seem to have eliminated the fuel system from the stalling issue.  However, based on paragraph 2 above, that doesn't seem possible.   I will entertain any suggestions.

As an aside, I have eliminated all of the AIR plumbing, EGR valve, and all of the vacuum related emissions lines on the intake manifold.  Charcoal canister is still in place, but not attached to the intake manifold.  I'm usually pretty good at diagnostics, but this one has me stymied.  Help !

Irish_Alley:
how does your oil look? if you put a drop on your finger does it run off or stay in a drop and stay in place

Rapid Roy:
I got my truck in 2015. Still had oem fuel pump. Replaced with new low cost pump from local auto parts store. After about a year, started having intermittent stalling after stopping at a store and starting again and going for a few hundred feet, Would pickup and go on. Finally decided to get a new one again in 2018. Got an AC Delco, and have not had anymore stalling issues since. Your pump could be causing the issue.

MIKE S:
I agree with poor quality fuel pump also. Another possibility is that in 1985 they used a non vented fuel cap. You also said that you don't have the carbon canister hooked up completely. You may not have any venting going to the tank causing it to create a vacuum starving the pump for fuel. Simple test would be to leave fuel cap loose and drive it and see if it still has a problem.

JohnnyPopper:
Mike's theory sounds like it's worth trying.

Kind of mind boggling when you kept the engine running then the pump kicked in...

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