Fuel pressure question

[Crock]

I think part of my problem was that my multi-meter is too slow. The prime cycle is pretty short and it wasn't on long enough to get a good reading. I grounded out the fuel pump wire on the diag. connector and held it for a few seconds more and got a reading of 11.56 after the inertia switch. I assume 1 volt drop for that distance is ok?

Also just for fun I pulled the intake and lifted the injector rail out of the lower and primed the system. None of the injectors leaked. (this may not have been the safest thing to do) So now I know the injectors are not leaking,tried another FPR and checked the voltage near the pump. I also pinched the return line and primed it,which didn't make the pressure go any higher.

Is my next step to pull the tank down and check the voltage right at the pump connection and if its good change the pump? Is it possible that I got a bad pump right out of the box.

 

[HISSIN50]

You can do all that or if you can safely do it, do a volume test on the pump. The fuel filter is an access point into the system.

A bad pump is possible. As you noted, test voltage at the pump connector. If you have any doubts of your wiring, you can run a fused jumper from the charged battery to the pump connector. You really should not drop that much voltage (assuming your battery was at 12.6 V).

 

[Crock]

Thanks Hissin50! I will try and search how to do a volume test.

 

[revhead347]

All the bigger pumps leak pressure. For some reason the stock pump holds it, and the bigger ones leak it all back in a few minutes. If the car runs fine and has good pressure when it's running, then I wouldn't even worry about it. Every single Mustang I've put a bigger fuel pump on has leaked back pressure just like you described, and I must have done about 40 of these pumps now.

Kurt

 

[RIO5.0]

All the bigger pumps leak pressure. For some reason the stock pump holds it, and the bigger ones leak it all back in a few minutes. If the car runs fine and has good pressure when it's running, then I wouldn't even worry about it. Every single Mustang I've put a bigger fuel pump on has leaked back pressure just like you described, and I must have done about 40 of these pumps now.

Kurt

What he said....The cranking deal is a pain and common....and at times embarassing when cranking it in front of Chevy's or the like......thats when you rely on the 3 prime trick...
I can remember returning my wifes brand new 94 to the dealer for this...they told me it was the new ignition they used...W.T.F. !!!! they didn't even get it.

mine did the crank thing for years...get in the habit of priming it a few times or pop in a new Walbro while you have it open and be done with it...

 

[Crock]

Ok...I am really starting to hate this car. I have now changed out the fuel pump with a 255 walbro and the new s hoseand filler hose seal. Still below 20 psi on the koeo. So to date I have swapped the fuel pump (new), injectors and FPR with working used ones and I have 12volts right at the pump connection with no visible leaks anywhere.....whats left. I had put a new fuel filter on about two years ago,but I have not driven the car much. (may only have a few thousand miles) It was not a motorcraft one. Is that a big deal? Could it be the pcm or a fuel pump relay? I thought the relay would either work or not work.

 

[toyman]

Ok...I am really starting to hate this car. I have now changed out the fuel pump with a 255 walbro and the new s hoseand filler hose seal. Still below 20 psi on the koeo. So to date I have swapped the fuel pump (new), injectors and FPR with working used ones and I have 12volts right at the pump connection with no visible leaks anywhere.....whats left. I had put a new fuel filter on about two years ago,but I have not driven the car much. (may only have a few thousand miles) It was not a motorcraft one. Is that a big deal? Could it be the pcm or a fuel pump relay? I thought the relay would either work or not work.

Two things come to mind. One, is the gauge reading correctly (can you test or access a different one?). And two, are you absolutely certain the used FPR is good.

I don't see where you tried clamping the return fuel line. That should put the pressure into the high 70's psi plus range if the pump is putting out to spec.

 

[ProKiller]

maybe a dumb question, but did you make sure you got the right pump? it wasn't for a carb setup right?