Fuerl Pressure problem1988 Bronco

lstill · Dec 10, 2015

Hey guys, hope some of u might have had a similar issue. Have a 1988 Bronco 2 v-6 5 speed 4x4. Got it from a guy that had spent loads of $$ replacing almost all electrical components ect trying to run down an issue with the Vehicle bogging and trying to stall. bought it , relocated a new ignition module to a heat sink on the radiator support and seemed to be ok....then week or so started it again. Turned out that the low pressure pump in tank weak so replaced it. Seemed to do much better for a couple of weeks and then started to give me a little hesitation ....so sprung for a new high pressure pump on frame rail, new fuel filter and even took the little plastic fuel reservoir apart because some of them had filters in them got it back together took off on a 60 mile ride trip ride and ran great till we started home....started stalling,trying to die. Got it home put fuel pressure guage on it starts out at 40psi and runs a bit and pressure begins to drop slowly to a point it stalls. I bypassed the relay so both pumps are buzzing away...seem to be running fine but still starts losing pressure after awhile. There is a access panel cut in rear panel so u can take rear pump out without dropping tank, pulled rear pump...Tank looks like new,all lines clean and tight...gonna follow the lines along the frame rail to fuel resivor and hp pump to see if there may be some kind of problems with the delivery fuel lines....this things got me stumped.....any thought appreciated. thanks Larry

enjr44 · Dec 10, 2015

New pump no longer means good pump!! Manufacture's QC departments have been turned into advertising departments. You are the new QC department!!

RonD · Dec 10, 2015

Is the "sock" on the in tank pump clean?

Have you tried running with gas cap loose?
EVAP system could be building up too much negative pressure in the gas tank making it harder to pump out fuel.
EVAP system gas caps are pressure vented to prevent this from happening, they allow air in once negative pressure gets to a certain point, like a rad cap works with coolant pressure, and just like a rad cap they can fail, it is uncommon but not unheard of.

On the fuel rail is the Fuel Pressure Regulator(FPR), Fuel Return line is attached to the FPR and also a vacuum line.
At high vacuum, idle, FPR is pulled open and most of the fuel goes back to the tank, so I would expect 30-35psi at idle, if you unplug this vacuum line at idle then pressure should jump up to 40+psi.
With vacuum line connected, as you raise RPMs intake vacuum drops and FPR closes a bit, fuel pressure should go up, did that happen?

Make sure FPR is hooked to intake vacuum(regular) source, not Ported vacuum source.

Regular vacuum is found between throttle plate and heads(intake valves), it has high vacuum when throttle plate is closed and engine is running, then lower vacuum as throttle opens.

Ported Vacuum is between throttle plate and air cleaner, it has low vacuum when throttle plate is closed and higher vacuum when throttle plate is open.
There is often a ported vacuum port on the very front of the upper intake, so in front of throttle plate, this would NOT be the place to hook up FPR

Fuerl Pressure problem1988 Bronco

lstill

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