Odd Fuel psi symptoms..w/in

[Rob B (shoebox)]

Pressurize the system (use the fuel pump prime connector if you want to) and watch with a gauge. Carefully clamp off the supply line (use something that won't damage the line). Shut off the pump and observe pressure. If it does not bleed off, the problem is from your clamp back toward the tank. If you don't have a leaky line, then it is probably the check ball in the pump.

One purpose of the check ball is to allow the line to keep some residual pressure, so that the engine will be easier to start on the next try.

[KnightFire]

Excellent theory!

However, the pressure goes right back to 0 nearly as soon as it reaches 40-50psi, thats with the key on. As soon as the fuel pump turns off (from priming the system) the pressure falls right back to 0psi again.

The only way it stays at 50psi is with the engine running. Is this a smart thing to do while the motor is running? I mean this sounds like the mother of all lean conditions, I just put a ton of money in the short block, last thing I want is to pre-detonate the new pistons.

This is why I'm so stumped! Unless I'm missing something rather obvious, which is quite possible...LOL.


KnightFire

[N20LT4Bird]

I've been watching this thread for a while and thought I'd jump in to lend Rob a hand. Knightfire, you dont have to start the engine. Deadhead the pump right after the line leaves the tank, before your filter. You'll have to make some adapters. Turn the key on and watch the pressure. If it bleeds off right away, the problem is in the tank- i.e. check ball in pump or the rubber line coming off the pump to the sending unit (leaking). If pressure doesnt bleed down, you know the problem is up front, FPR, or injector etc. (All assuming your lines arent leaking fuel.) I would bet on check valve or leak between the pump and sender.

[PiercedJD]

I have seen computer problems where the injectors stay open and cause loss of pressure. usually this is seen as the car running fine while it's on, then you come out to start it after stopping at a store and it is difficult to start ( flooded) then once it starts it runs fine until you go to start it again, which might be many hours later (fuel has drained down past the pistons, and fuel pump takes a while to reprime the system).

the tattle tale for this condition is pulling the oil cap, or dipstick and doing the *sniff* test. the oil will have a fuel odor, as it has been mixing with fuel which has drained down past the piston rings while sitting.

just another thing to consider.