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Discussion Starter · #1 ·
1991 bronco full size 351 e4od intrmittet problem only when weather outside is very hot say over 90 degrees after driving for 4-5 hours truck will start to stall have to pump gas pedel and keep revs up but eventually it stops running have to let cool down 30 45 min then runs for a while again but will do same if weather is cooler say 80 degrees or under can drive all day long have changed ignition modual-map sensor fuel filter did tune up etc nothing helps finally took to ford dealer bunch of idiots!!! said they cant duplicate conditions said take to a dealer where weather is always hot said mabey vapor lock and to wrap fuel lines has anybody had to do this ?if so whats easiest way do i have to take the upper intake off to wrap the fuel rail ? please help thanks
 
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Discussion Starter · #4 ·
not the fuel pump thats for sure checked with a gage its within factory specs running about 35-40 psi all the time
 

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Next time it does it check for spark.The ignition modules are known for heat related failures.I've never heard of anyone having vapor lock problems,and I live In about as deep south as you can get.

Billy
 
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Discussion Starter · #6 ·
And you've checked the fuel pressure while the problem is occurring? If not, I still vote fuel pump - they'll work great once they cool down but when warm they'll "fail." I believe the pump gets so hot it'll vaporize fuel as it passes thru; technically EFI is not supposed to vapor lock like a carb, but I believe this is a form of EFI vapor lock "so to speak." The problem is exaggerated as the fuel level in the tank gets low, the pump is immersed in less fuel and also runs hotter as a result.

Healthy pumps will not exhibit these symptoms but IME this is how many of them start to let you know they're tired.
 
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Discussion Starter · #7 ·
Mine was doing EXACTLY the same thing while driveng between Tucson and Phoenix. It wouldn't do it while driving around town but that long drive in 100+ heat going 75 with 35"mt's would do it every time. let it cool for 30-45 min and its fine for about 45 min and then does it again. Hasn't happened since I changed the fuel pump. (which was up to spec while cold).
 
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