1988 Ford Bronco



January, 24, 2009 AT 11:07 AM

Engine Performance problem
1988 Ford Bronco V8 Four Wheel Drive Automatic 289764 miles

Hello, I have a 1988 full size ford bronco 5.0 efi with aod tranny. For the past several years I have experienced the same engine sputter and stall that many of you have also experienced. Basically I have attributed this problem to what would be considered vapor locking. Yes even with efi.

Here is the problem. There are two types of gasoline that are produced throughout the year. Summer blend and Winter blend. The summer blend runs fine. However, once the weather turns cold in the U.S.A./Texas, Nov./Dec. The refineries start producing the winter blend gasoline that contains chemicals (VOC's?) That keeps the gas from freezing. I happen to live in a region of Texas where it rarely freezes. In fact, our typical winter weather can reach 80 to 90 degrees. On these days, and specifically in Feb/March when temps can be higher than 95 degrees, the gasoline in the gas tank will boil. When the gas boils it creates vapors thus vapor locking the engine and/or fuel lines. Originally I thought it was the fuel filter. By the time I replaced the fuel filter (15 to 20 minutes) the engine would start and run fine. On one occasion I replaced the fuel filter 3 times within 10 miles of driving. I carry spares and reuse the old ones. However, now I attribute that fix to releasing the pressure/air/vapors in the fuel line, not the fuel filter. Yes I have replaced the MAP sensor, due to another problem, done a complete tune-up, has good fuel pressure and both fuel pumps are working fine. Etc. Etc.

A mechanic told me a few years ago about this summer/winter blend gasoline. He suggested using Marvel Mystery Oil in my gas tank especially during the winter months. And no, this is not a sales pitch for Marvel Mystery Oil (MMO). However, it did help for a few years. At least I wasn't replacing fuel filters 2 to 3 times per month during the winter.

This past winter (2008) and now I am expecting it to happen this winter (2009), even after using the MMO, my bronco will sputter and stall. If I wait an hour or two, the bronco will start and drive on but this is very inconvenient.

So with that brief history. Here is my question. Does anyone know of a cure to this problem?

Would replacing the charcoal canister help to allow the vapors to escape? This was suggested by another mechanic. My bronco still has the original canister. There is rougly 290k miles on it. FWIW, I have only replaced the tranny (2 years ago) and the engine runs strong. KOW (Knock on Wood).

Is there a way to release the vapors from the fuel line without having to disconnect the fuel filter?

Thanks in advance!
(edited to correct spelling)


4 Answers



January, 26, 2009 AT 7:23 PM

Unfortunately I dont think gas vapors has anything to do with your problem. I would first start by checking fuel pressure with a gauge and see what it says. The fuel injection system uses a fuel pressure regulator so fuel is constantly being pushed back into the tank so vapor lock cant occur.



February, 4, 2009 AT 1:41 AM

Thanks for the reply Tim.

If I remember correctly, when I checked the fuel pressure a few years ago, it was approximately 42psi. I believe that is within the standard operating range for a 1988 Ford Bronco (Full Size) with EFI.

It was my understanding that with EFI you could not get vapor locking. However, a mechanic friend of mine has told me that it actually is possible. Is that correct?

If the fuel regulator was not working properly how would that affect the performance of the vehicle? Would it allow vapor lock to occur?

Also, why does the vehicle only stall on warm to hot days (80+ degree temps) using the winter blend gasoline and not on extremely hot days (105 degrees) using the summer blend gasoline?



February, 4, 2009 AT 5:38 AM

First you would need to check fuel pressure again. A faulty regulator can cause high fuel pressure, low fuel pressure or fuel pressure drop off when trying to hold pressure. The vacuum diaphram could be ruptured causing fuel to leak directly into intake. When was the last time you checked it for codes? Sounds like your stalling prob lem is a bad tps, or egr problem not gas blends



February, 20, 2009 AT 9:52 AM

Thank you. It did not generate any codes. I will check the EGR valve. I replaced the throttle positioning sensor (TPS) and the MAP about a year ago.

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