That infernal stalling problem again . . .

[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...

[Irish_Alley]

the thing im thinking about with the oil as we've talked about it on here before is the fuel pump diaphragm can leak into the engine block allowing the fuel to drain back into the tank. and this would explain the long cranking time.

[VileZambonie]

Leave the fuel cap loose as MikeS mentioned. Investigate how your tank is vented. Reinspect your hoses coming off of the tank for potentially kinked hose.

[haroldwca]

Thanks for all the replies.  In order:

(1) The oil is fine.  There doesn't seem to be any cross-contamination.
(2) If I remember correctly, this is the third fuel pump on the truck since the stalling issue first occurred (about three years ago).  There was a sufficient span of time between each replacement that I doubt they were from the same lot #.  It would be highly unlikely to have three bad pumps in a row. (I realize that doesn't mean impossible, but I will play the odds.)
(3) I have replaced the fuel cap, but I don't remember whether I tried driving with it loose.  Both the prior cap and the new one are vented, and both passed the "blow test" for the vent mechanism.
(4) Regarding proper venting to the tank, this is the kind of problem I was suspecting, but I haven't yet focused on tracing the vent lines, as I was trying to positively verify or eliminate other possibilities. 
(5) I really don't experience a long cranking time.  It either starts well, or not at all. I will investigate the vent lines and try the loose cap test drive.  I will respond with what I find. 

[MIKE S]

Mechanical fuel pumps aren’t made as good as quality as they used to be. They are not massed produced anymore because production vehicles don’t use them  so they are not held to a high standard. I used to cut these things apart to figure out what failed. There are two check valves pressed into the housing. One is probably loose or sticking. They are usually staked in and have a tendency to get loose or fall out. That will cause pressure or suction problems. You can get an inexpensive pressure/vacuum gauge and test the pumps pressure and suction. Heat may play a role on expansion of the housing and causing the valves to leak. I would replace the pump with the best quality you can get and do a little surgery on the old one and see what it’s made of and it will give you a little insight on how it works. 

[SlayTank]

Not sure if this would help/ is the case but I figure I’d pipe in with my experience. I have a 85 Toyota with Weber carb and aluminum intake. It would start easy if it was cold but like you said I’d drive it go into a store go inside for about 20min I’d come back out and it would crank crank crank. (Not exactly your problem but hang on) And spew black smoke out the tail pipe and finally sputter to life. Weber’s need 2.5 psi so I added a fuel pressure regulator and gauge, I also made a little air scoop for it with plans to turn into snorkel. One day getting into the truck I walked passed the scoop and hear bubbling. The heat was causing the fuel to boil in the line expanding it and pushing the float off its seat thus flooding it. Now to fix the issue I ran some hard lines where I could instead of the rubber hoses. And put some tube/line insulation on them. Or just insulate the rubber lines I’m sure would be fine too.
Like this

https://www.jegs.com/webapp/wcs/stores/servlet/SearchResultsPageCmd?Ntt=Thermal+Heat+Sleeving&requestYear=&storeId=10001&catalogId=10002&langId=-1&year=&make=&model=&submodel=&engine=&Nrpp=&No=&persistYmm=false

Google thermal heat sleeving


Long story short try to insulate those fuel lines because I think you’re on the right path thinking about the heat and rerouting the lines. Now insulate them from the heat and prevent boiling the liquid fuel. Liquid pumps don’t pump gaseous states of matter very well.



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[haroldwca]

I've owned this truck for 14 years, and today is the first time I've entertained the fleeting thought of selling it.  Here is what has transpired since last post. 

I had eliminated everything from fuel pump forward to the carburetor.  Even though I had dropped the fuel tank earlier, I did it again.  Having previously said that I inspected the fuel pickup, I realized that I really hadn't investigated the operation of it.  I just looked at it, then set it aside as I peered into the fuel tank.  So I repeated the whole ordeal.  Upon removal of the fuel pickup I inspected and checked the function of the vent tube.  It seemed excessively difficult to blow through it.  I deemed it worthy of replacement since it is 34 years old, it was already out, and its function seemed questionable.  After reassembly, I performed a road test.  Same result.  Bring up to operating temperature (not hard to do here in southeastern NC lately), pull over and shut off the engine.  Upon re-start about 10 minutes later, it will drive about 500 to 1000 feet, then sputter and die.  It will restart once and then die immediately.  It will not restart the normal way. 

As a matter of an easy check, I bought a new fuel pump (the 4th) and installed it, since the 3rd pump was about 1 1/2 - 2 years old.  Again, same stalling problem.

What I have found is that I can restart it if I feed fuel through the bowl vent of the carburetor.  If I remove the output line of the fuel pump, then restart the engine using the described method, the pump first pumps no fuel for about 5 - 8 seconds, then spurts a small amount of fuel for about 4 seconds, then pumps normally for as long as I keep the fuel supplied through the bowl vent.  Reattaching the pump to carb line, I can then drive away if I am VERY gentle on the throttle until I am up to about 45 mph.  If I remain at speed, I can drive until I run out of gas in the tank.  However, if I have to stop at another stop light or sign, it will stall again upon acceleration or if I remain idling for an excessively long time.

I have already re-routed the fuel line from the tank to the pump.  It seems as though the fuel is vaporizing in the fuel line between the tank and the pump, but I have no idea why.  The stalling began before I made any changes to the fuel system. 

Some suggest ethanol as the culprit.  I don't know nearly enough carburetor owners who are experiencing this problem (none, actually) for that explanation to make sense without a lot more evidence.

I realize that I have already been pro-actively eliminating everything in the fuel system as a possible problem, but that is where I am.  With that huge caveat, does anyone have any other suggestions?

[bd]

Leave the fuel cap loose as MikeS mentioned. Investigate how your tank is vented.  Reinspect your hoses coming off of the tank for a potentially kinked hose.

Did you do this ^^^^^ ?

Assuming that you are running a mechanical fuel pump actuated by the camshaft, when you had the fuel pump off did you remove the pushrod and inspect both ends for unusual wear patterns and verify whether the pushrod imparted a suitable stroke to the fuel pump arm (IIRC, 3/8" - 1/2")?  On very rare occasion, the camshaft eccentric can wear flat. 

While the pushrod was out, did you inspect the flanks of the pushrod for scoring?  If at some time in the past someone inadvertently installed a long bolt into the bolt hole that intersects the pushrod guide tube and scored the pushrod, it can bind the pushrod and limit travel.

Did you verify that the pushrod is straight by rolling it across a flat surface?  If a fuel pump was improperly installed such that the pushrod slipped off of the arm and bound up against the side of the fuel pump arm and the fuel pump was bolted down tight against the block, even if the engine was not started before the problem was corrected the pushrod could be slightly bent, again limiting pushrod travel.

Regardless, since it is back together, perform standard fuel pump draw (>20" Hg), pressure (5-7 PSI) and delivery (1 Qt in 20-30 seconds of cranking) tests using a proper gauge, adapters, fuel safe receptacle and a fully charged battery.  In the process, collect a sample of fuel in a clear container and allow it to sit undisturbed for 15-20 minutes then inspect it for evidence of separation and cloudiness (fuel contamination).  Update us on what you discover.

[SlayTank]

Maybe give a electric pump a try?


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[haroldwca]

Thanks bd for your suggestion.  Up to this point, I had been persistent in performing thoughtful diagnostics to discover the cause of my trouble, and I may try your suggestion at some point. However, for now I have decided to try the electric fuel pump for a pragmatic reason.  I simply need my truck to run, as it is my daily driver. Slay Tank, I had considered an inline electric fuel pump for a while, but that seemed like treating the symptom, rather than the cause.  However, since school is out now (I am a high school teacher) I need my truck to run for more than short trips.  Living less than three miles from the school, the symptom did not present itself, but I have many summer projects that require mobility.  Therefore, I bought a $9 inline fuel pump and installed it this weekend.  So far, no stalling !  The temperatures here have moderated significantly for the past week, rising only to the mid 80s each day, so I am not completely convinced yet that I have alleviated the symptom.  I will keep everyone posted as the mercury hits the high 90s.  Thanks to all who have contributed to the thread!

[SlayTank]

Harold, I completely agree with you about fixing the problem correctly. I’m not as good with written words as bd or as thorough thinking. My thought was to eliminate the pump and go from there. It has the most moving parts and like with weapon systems more parts = more chance for failure. It seems like the cam or drive system (pushrod) is the last piece in this system that hasn’t been checked.

Thanks for your service as a teacher by the way. Very important and under rated career.


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