I have a 86 Bronco II with the fuel injected 2.9L V6. I just recently acquired it and it's iritating problem That is, when the gas gauge gets down to half tank, sometimes a little below half, it acts like it's out of gas(cough, sputter, jerk) and dies. When you try to restart it it will try to run but dies immediately. After setting for 15 / 20 minutes it starts right up but runs a little rough until you top the tank off, then runs good again! It's done this 3 times now, and the first couple times I immediately thought of the ignition module. But, after determining it had a strong spark by pulling the coil wire and shorting it to the block decided the module is ok.
Each time it's done this has been running at least an hour - yesterday was after a two hour drive to Long Beach, Wa.
Any ideas or suggestions would certainly be appreciated!

 

Sounds like a weak fuel pump. Checking fuel pressure at the schrader valve is almost as simple as checking tire pressure.

Harbor freight will sell you a fuel pressure gauge for about 18 bucks.

 

Also sounds like your float in the tank is giving a false reading. How many miles from full tank to half do you get? I agree on checking fuel delivery for proper fuel pressure. You may have a weak pump - could be the in-tank low-pressure pump or the frame-rail mounted high-pressure pump. When was the last time both fuel filters were changed? Could also be experiencing blockage in those or the in-tank fuel pickup sock filter. You may want to drop the tank, drain it and flush it while you're at it.

 

Hey, 87 XLT & Kernel-Panic!
Thanks for the quick replies, but both pumps are new - replaced them last week after the first time it died. Both pumps were noisy so figured that was the problem so had my mechanic change them out. Turned out the old pumps weren't delivering the required pressure - 19 lbs running. Just had the pressure checked this morning and was 39 lbs not running(ignition on) and 35-36 lbs with engine running. The mechanic said everything appeared normal inside the tank - clean, no foreign objects floating around in it.
The first time this happened I sat about 15 minutes while the wife brought me 5 gallons of gas - gas gauge said I had a quarter tank. I put the gas in and it started right up. Went to the gas station and it took 11 gallons to fill it.
The next time it happened I tried to start it about every 5 minutes and after the third or fourth try it started but ran kinda rough until I went to the gas station and filled it. This time the gauge showed it just below half and it took right at 10 gallons to fill.
Then yesterday, after the third time of dying, I sat about 15-20 minutes and it started right up. Ran rough until I filled it with gas and smoothed out
Is there some way this could be a vapor lock situation - anyone have any experience with something like this with a B2 or Ranger? Next time this happens I'm going to unscrew the gas cap to see if maybe a vacuum is forming in the gas tank thus prevent gas from flowing???
Again, would sure appreciate any help I might get with this matter

 

The head pressure from a full tank will help a weak pump, but you have a new pump so go figure??

When you checked fuel pressure did it react correctly when you removed the vaccum line from the pressure regulator? It should jump up. Does it hold pressure with the engine off?

Your 86 is not equipped with a check engine light so the only way to know if theres any trouble codes is to pull them. Has that been done?

Dont think it's a vacuum in the tank problem, but as you say it could'nt hurt to run with the cap loose.

If you have a vacuum gauge read the directions that came with it & do the test for a clogged exhaust when it's acting up.

 

With the cap removed, it will throw a code (if it's like my '87). The cap should be a vented one, if I recall correctly. Considering the symptoms, I am going to take a stab at the FPR is on it's way out. I would agree, check for the reaction when you remove the FPR vacuum line. If it doesn't jump up to right at or around 60 - and you happen to notice a 'mist' especially - then I would suspect the FPR. Also could be a vacuum leak somewhere that just happens to rear it's ugly head with a half-tank or less. I can't remember where the carbon canister or associated components feed from, but a possibility is a bad vacuum line or a bad canister in play of the fault. You should pull codes with a code reader or use the test light / voltmeter method. Another good point 87 makes is the vacuum test. Could possibly be a bad cat or clogged exhaust in play, too. One 'trick' you can try when it dies is to cycle the key on and off several times (like if you were priming the fuel system after working on it) and see if that helps. Something keeps pointing me towards the FPR, though. May not have a bad leak in the diaphragm, but it could be failing. Anything ignition-related would act up more often, especially if it were the TFI module on the distributor or moisture in the cap or faulty pickup / stator.

 

my $02:

I am leaning towards air in fuel line, probably caused by weird in tank things.

When I took apart my fuel pump gage assy, it had a return line that directs fuel directly at the intake filter balloon. air bubbles will just circle around at low tank fuel levels
the tank pump sits at about 1/4 tank so if the connecting rubber hose goes bad, you'll get air. My rubber connector was melting, bought new silicone tube. Could also be the in tank filter is collapsing.

if you have it apart anyways, have a look-see.