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Fuel Pump Pressure Testing

I had to Pressure test my fuel pump because I was receiving a lot of signals it was going out. The truck was bucking at 2500 RPM, Bogging at full-throttle, stalling in 4×4, and also totally broke down 11 miles up a trail last time I went off-roading.

That last one was the really inconvenient symptom…

The specs for the Ford Ranger’s fuel pump are:

1988-94 2.9, 3.0,4.0  @ Rest 35-45 @idle 30-45

Results As measured:

All electronic connections OK

Rest: 32 psi  Idle: 26 psi (Standard Deviation +3) so rest OK/ Idle (fail)

Secondary symptom: fast pressure fall on load/ FPR (known good) doesn’t effect trim when removed from vacuum.


Weak Pump

Step By Step Instructions:

fuel pressure gauge

Idle test

Ensure the pump has is functioning/ fault is not electrical

Hook Up gauge

Turn ignition on and off with 10 second pauses to let fuel pressure build (per book… you may just crank it). Clear the gauge to remove air (Step not in video)

Run engine and check pressure (pass/ fail)

Pass OR Fail

Disconnect vacuum to Fuel Pressure regulator, pressure should jump to high spec. (Pass/Fail)

Pass Pass – system OK

Pass Fail – Fuel Presser Regulator may be faulty

Fail Fail – Fuel Pump output low (Check lines for obstructions, replace fuel filter, etc. before just ordering the pump)

REST Pressure test (not in Video)

Raise pressure to spec, kill engine. Pressure should remain in SPEC for at least 1 minute (Fail/Pass)

Pass – system OK, no leaks

Fail – System leaks/ bad pump check valve/ faulty FPR

Vapor Lock Test – Bonus!

If gauge is moving a lot perform an “Air Test.”

Build pressure in gauge, stick end of blow-off hose in an approved container with a bit of gas in it.

Purge the gauge slowly, Check for air bubbles (Pass/Fail)

Pass – no leaks

Fail – Leaks in fuel lines/ joints.

Check here for instructions on how to replace the fuel pump

This post first appeared on Paul's 4x4, please read the originial post: here

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Fuel Pump Pressure Testing


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