LT1-LT4 Modifications 1993-97 Gen II Small Block V8

low fuel pressure at idle

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Old Apr 27, 2009 | 09:58 PM
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Question low fuel pressure at idle...bad FPR?

when my car is at idle my fuel pressure is at 32psi. I have changed the fuel filter and the fuel pump. My car is a 93 so my question would be what kind of aftermarket FPR would be my best selection and or would just replacing it w/ a factory one work? I am doing a cam swap right now (230/236) with LS7 lifter 1.6rr and matching springs. So i will already have the fuel rail and intake off.

Any advice will help out.

Last edited by litch2004; Apr 27, 2009 at 11:30 PM.
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Old Apr 27, 2009 | 11:55 PM
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I have a similar problem with mine idling at around 35 psi. I don't know whether to go with an adjustable fuel pressure regulator or a stock one. My fuel system is all stock.
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Old Apr 27, 2009 | 11:58 PM
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i think that is my only option left is to replace or upgrade it. Everything else has been replaced besides that and the injectors
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Old Apr 28, 2009 | 07:43 AM
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Are you disconnecting the vacuum port when checking it? The pressure will change (increase) a good 6-8 lbs., make sure your doing this when checking the FP, Now if your looking for a decent inexspensive FPR, i got one from O'Reillys, it was cheaper then the factory (non adj.) unit, it worked fine, never had an issue with it, plus it came with a good warr.
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Old Apr 28, 2009 | 10:52 AM
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No i havent disconnnected the vacuum line. So when i disconnect it and check the pressure while it is at idle what should the pressure be at to know that my FPR is good?
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Old Apr 28, 2009 | 11:09 AM
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41-47 key on not running

at idle, should decrease 3-10 psi.

so anywhere between 31-44 at idle.

this is according to my chilton manual, 1997 and earlier. 1998+ has higher numbers.

is there a problem with the car, or do you just feel its too low? everything you said shows a proper pressure holding fuel system.

Last edited by trippinholyman; Apr 28, 2009 at 11:14 AM.
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Old Apr 28, 2009 | 11:36 AM
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As stated, disconnect the vacuum line to the fuel pressure regulator and test your fuel pressure. You also should test if your fuel pressure holds while under load at high rpms. If it checks out, you're good.

Another thing, don't waste your money on any adj fpr's. Fuel delivery is computer controlled.
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Old Apr 28, 2009 | 07:30 PM
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Originally Posted by trippinholyman
41-47 key on not running

at idle, should decrease 3-10 psi.

so anywhere between 31-44 at idle.

this is according to my chilton manual, 1997 and earlier. 1998+ has higher numbers.

is there a problem with the car, or do you just feel its too low? everything you said shows a proper pressure holding fuel system.
Like you said i had read that it should be between 41-47 KOEO (key on engine off) but should only decrease 3-5 lbs i believe is what my hayes manual stated. Cant quote that for sure because my buddy borrow my manual. But mine drops all the way down to 32lbs so i thought mine was bad. So i guess mine is working correctly.
Thanks for your help
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Old Apr 29, 2009 | 03:31 AM
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Originally Posted by ss.slp.ls1

Another thing, don't waste your money on any adj fpr's. Fuel delivery is computer controlled.
The PCM will only adj. the fuel tables so much, after that your on your own, i bought my adj. reg. because to my surprize it was cheaper then the non-adj. unit, but i found that setting the pressure higher slowed my car down (MPH) at the track on back too back runs, so the PCM couldn't currect the tables in a 8-10 lb. difference, the non-adj. unit was 76.00, the adj. unit was 55.00, plus it was fun playing with the pressure to see if it helped or hurt.
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