88 BII fuel pressure drops 2 nothing (pumps still running)

[smallbl0ck]

I have an AAS DEGREE in AUTOMOTIVE TECHNOLOGY... i have worked at several shops over the years.... this is the first ford i have ever owned and i am stumped!!!! One of my old bosses (was a ford master tech in the 80s) is stumped!! Iv called every Ford tech i have ever met..... DRIVING ME CRAZY

Here is the deal.....I have an 1988 ford bronco II 2.9 efi... The truck runs GREAT untill you drive it arround for about 30 minutes (long after it has reached operating temp) then the fuel pressure begins to fluctuiate...normally 30psi down to 20 and slowly drops to nothing... After it has cooled down it starts back up again(with full pressure??? Not throwing any codes

I even bypassed the relay to give constant power to the pump...... both pumps running with full power//just no pressure! All lines are clear and free flowing

I know what you are thinking.... Bad high pressure pump right,,, wrong/ Both pumps are brand NEW! ("new filter ofcorse")

i thaught i might have gotton a defective high pressure pump from parts store(it happens) so i got another one "different brand" Same problem..

Then i replaced the THIN FILM MODULE on the distributor, and bypassed the INERTIA SWITCH/// then i yanked off the the fuelpressure regulator to see if fuel is even flowing,, nothing more than a trickle while haveing this problem?!?!?!?!?!

If Any one knows Anything about this Problem.... PLEASE PLEASE PLEASE RESPOND before i set it on FIRE!!!

Thanks a TON!!!

 

[andre]

fuel tank vacuum lock up

vent valve block take gas cap off ??

fuel pressure regulator vacuum problem

try to block return to tank check if pressure go back up ??

electrical load test on pump tank and frame mount 10 amp load test

lot's of ford here never had this problem

hope help to find problem

 

[smallbl0ck]

The fuel pressure regulator & vaccuum are fine.... but your suggestion about the "tank vaccuum lockup" sounds verry plausable..... Thanks a ton for the suggestion, i might even pressureize the tank with a compressor......... ill keep u updated

......I have always been a ********* chevy guy, this is my first ford I love it! I bought this thing with 250,000 original miles on it!! iv never seen a s-10 blazer get half that with little to no engine work done.....

I Still love my chevy but i now have a taste for fords....

 

[86nevadaBronco]

I have an 86 Bronco II with EFI 2.9. We had a week of 100 plus temps and the same stalling problem happend. The truck has 2 new pumps and both were running, but no fuel pressure. There was a lot of air in the fuel line, as if it had vapor locked. After I pulled the fuel filler cap off and released a large amount of air out of the tank as well as from the shrader valve on the fuel rail...the truck started. I have since replaced the filler cap and regulator, as well as made sure the vent line was not plugged. Havn't had any problems since. I too have An AS Degree in Auto Tech and have owned 26 different fords of my own.....never have I seen this problem.

 

[andre]

no expert here just love ford and i have ad ford for many year

my work auto repair in nort american car but mainly bmw audi vw

if it fix the problem

B) llol

tc all