What is ideal fuel pressure (PSI) at idle? I'm running an L98 out of a 89 vette and an on going issue has me testing the fuel system. I ran the car today and was getting 36psi with the vacuum line connected. What I did notice was after I shut it down the pressure dropped to zero in around 30 seconds. Oh, the engine is stock with the exception of Ford injectors. Thanks Much

 

@ idle 43 ish vac disconnected. ;39 connected
The instant presure drop shows you have a leak somewhere; Faulty pressure regulator / check valve in tank / injectors maybe

 

Could you possibly have your #s reversed? Today I played a bit more and did a few tests. To start the day it was doing the same as yesterday, running at idle with around 35psi vacuum hose on, around 45psi with hose off. Shut it down and the pressure dropped back to zero. The gauge is a 6" Taylor that was certified for Nuke testing taped to the windshield. One thing I noticed was with key on I didn't get the 2 second pump run at all times?? I clamped off my return hose to test both pump output and FPR. The pump gave me better than 80psi with the stock Jaguar pump and no more bleed down so the injectors are OK and the FPR is in question. Now for the strange part after the pressure run up the FPR seems to be holding the shut down pressure for a lot longer? As an aside ever since I built my ride I have always had a fairly long crank time till it fired up, almost like it was needing some oil pressure before it would start, is this normal? All suggestions welcome

 

Late at night ;fixed now

 

That would indicate you are not getting the 2 sec prime from the relay and are running on the oil pressure switch only.If relay working correctly , fire up is almost instant

Check relay operation and connections
Jumper the red / orange at the relay connector and see if pump runs; that will confirm that wiring to pump is good.You are then left with faulty relay ( not uncommon with age ) or broken relay control link back to the ECM
Because the relay and OP switch are in parallel , you can have one go out and not realise it because engine will still start

 

Thank you, it may take a few days to get back at it. Between a 3 month old grandson and shooting Skeet on Sundays with my Son's it's a busy life for this disabled vet. First will be the relay check. I put this car together originally about 9 years ago and that slow start was always the way of it. I figured (wrong) that the vette might want to see some oil in the mains before the fire up! When I first put this together I bought Diacom to get read outs and as recent as this summer I never got a code for the relay, if there is a code? Once I iron out the fuel delivery issues, including the FPR, I may post the real challenging problem this TPI engine has had for a few years. Thanks again

My life: Past and present
http://crayonmedia.com/wayne/

 

The computer doesn't care about the fuel pump relay. It just turns it on when it feels the need. Even though it monitors whether the pump is getting voltage or not, it will give no indication of a relay problem. Seems to me, this would have been a seriously easy tidbit to add..... Ah well.