- key on engine off, pressure spiked to about 50, then dropped to 43.
- Engine idling, pressure was 38
- Engine idling with FPR vaccum removed, simulated WOT pressure was 45
- taped gauge to windsheild, actual psi at WOT was 40 throughout a 3000-6300 rpm run

My engine is consistently cutting out at higher rpms (6000+), but while i felt the car cutting out, the fuel pressure held steady at 40psi. Still, i though the acutual WOT pressure and the simulated (FPR vaccum removed at idle) WOT pressure are supposed to be about the same. Does the 5 psi difference i see indicate a faulty fuel pump? From what ive been reading, most guys with real pump problems are getting much lower (low 30s) WOT pressure than me, but i want to be sure before i eliminate the pump as a problem. I didnt notice any fuel when i removed the FPR vaccum line, so im assuming it is ok.


I've got SVO 30# injectors and a mail order tune.

 

Pump or filter or regulator. It should loose nothing at full throttle. If it does it's not running up to par.

 

LR, the relieft spring might be getting soft if it's old.

 

im not sure how it works and id think pressure and volume should be directly related but at the shop i work at they often test the volume of a pump to make sure thats not a problem either.

 

Yea --know about that!!!!!! The spring still has life in it yet,Sometimes it's 300lb/in --sometimes it's 25lb/in-- go figure. Most of the time it's just a handy thing to take on a picnic.

 

Racer man don't figure it has anything to do with the spring.

 

replace filter, recheck, if the same, its the fuel pump

 

yeah my post was in response to the original fuel pump question, nothing to do with the spring. anyways i just wanted to point out that not only pressure has to do with fuel getting to the engine, volume also has something to do with it and is often checked after a fuel pump is suspected and the pressure seems reasonable.

 

Just kidding ya Racer.
Bret might be making a funny

 

Ok, ill try changing out the filter.

If i see the same results, what else can I do to eliminate the FPR as a problem? MY FPR did not have any fuel in the vaccum line -- is there anything else to try other than replacing it too?

 

No:

 

When your fuel pressure gauge is reading 40psi, what it the MAP reading? If you were getting a lot of pressure drop in your intake track, and MAP was running appreciably less then barometric pressure, the vacuum compensation could be pulling the fuel pressure down.

Remember... you are trying to hold a constant 43.5psi DIFFERENCE between the pressure in the rails and the vacuum in the manifold.

 

whats the stock fuel pressure for an lt1 car

 

41-47 Iirc

 

The injectors are sized based on a 43.5psi difference in pressure between the fuel rails and the intake manifold. That means at idle, vacuum compensation line disconnected, you want to see 43.5psi, with anything between 41-47psi acceptable (as Dave pointed out). Reconnect the vacuum line, and the pressure will drop proportional to manifold vacuum, or a 6 to 8psi drop below the "no vacuum pressure", with a stockish cam.

When you go WTO, max engine load, you want the fuel pressure as close to 43.5psi as you can get it. As noted above, if you have a poor air intake system, you can still see a vacuum in the manifold at WOT, and fuel rail pressure will be reduced accordingly. To keep things in perspective, if the pressure drops from 43.5psi to 40psi, injector flow will drop off by about 4%.