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fuel psi at rail?


jaredssc17

jaredssc17

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i cked my fuel rail psi and at key up its 30psi. idle is 30psi and highest i could get it to go is 36psi by reving the motor. its a 97 4L. i called the parts store they told me the pump is rated at 70 to 90 psi? wif! i have a ck eng light on for lean b1 and b2. changed the fuel filter bout 600 miles ago(also egr iac and both b1 and b2 o2's). truck has 100k on it. what should i be getting from the fuel rail as a reading? this ck eng light is kickin my butt. this is my dd. cant have down time, i think its time for a pump and screen. part store said its 79 bucks for the pump, 8 for the screener. but its 99 for the whole sending unit, pump and all. thinkin about going with whole assy. ne ideas would help.
 


almostclueless

almostclueless

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The one time I've looked at my 98, it had 68PSI.


I would suggest ensuring what the problem really is.....if the wiring isn't providing full battery voltage at load, a new pump probably won't change that.
 

eric17

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my 93 was 34psi before i fixed the vac leak on the fuel pressure reg, it gain 4psi after that and ran night and day difference, before it was missing and running like complete shit while just cruising down the road.
 

Bird

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The return fuel systems (pre 98) should show around 40-42 psi with the engine running and the vacuum line that runs to the FPR disconnected - with the vacuum line connected - usually around 35 psi.

The returnless systems (98+) are set up for 60-65 psi.

Bird
 

MAKG

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Spec is 40 PSI key-on-engine-off (no need to disconnect the vacuum line and make a leak), and 32 PSI at idle, at sea level (it will be higher at high altitude).

If it won't hold pressure with the key off, a blown pressure regulator is likely. This can also cause a miss, which means excess oxygen in exhaust (HEGO sensors don't know anything about fuel, so any miss -- even a pig-rich miss -- can trip lean codes).

You can confirm a blown regulator by idling the engine, turning it off, and pulling the regulator vacuum line. Liquid fuel = definitely blown.
 
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