anybody got any ideas on this? (fuel pump issue)

[BadVr4]

on my dsm, i have an ems and a aeromotive 1000 fuel pump. i used to turn my key to on without starting the car, and the fuel pump would turn on. i tried starting the car today, turn the key to on, didnt hear the pump so i thought that was weird. i turn the key, the car starts. fuel pressure goes up to normal psi and then falls off to zero. car runs for a minute, and the gas light comes on, and the car dies. thought it may have ran out of gas so i added 5 gallons, turn the key back to on, couldnt hear the fuel pump. start the car, and it starts up fine but the fuel pressure gauge reads no pressure. What the hell is going on?

 

Hook a test light to the pump & see if its getting power, no idea how it could run on zero f/p. /ubbthreads/images/graemlins/dunno.gif

 

[Terry Posten]

There is a dual fuel pump circut that the ECU controls and uses the MPI replay to switch. Very confusing but in laymans terms it is the fuel cut-off after an accident so you don't pump gass all over the place.

What happens is that the MPI relay charges the pump for startup until the cam angle sensor reads the motor spining, then the MPI replay switches to the main circuit as long as the motor is running.

In short, you have either a bad MPI replay OR bad ECU.

Try a relay first because that is simple. If that does not fix your issue, you need to look for a ECU swap.

Wiring could also be an issue but that is a VERY small possibility.

Your odds are:

10% MPI replay
89.9% ECU
.1% wiring

Sorry.

 

If the fuel pump isn't priming and it isn't staying on after you start the engine, that's the mpi relay and it's not ecu related.

 

[BadVr4]

i have a brand new aem ems in the car, how could that go bad so fast?

 

[Terry Posten]

I missed the AEM EMS part. It was late.

I can't help, sorry.

In a stock setup, the ECU controls the MPI replay and when the key is turned to the "on" position (before and during cranking), a 12 volt signal is switched to the pump to allow the fuel system to "prime". It is a "voltage bypass" of the main control to pump. Once the ECU sees a signal from the CAS, it switches out that bypass circuit (again, part of the MPI reply) and the main pump circuit takes over.

So, does the car start and then run for 5 sec and stall with no pressure?
or
does it not start at all.

Shoot me a PM with your email address and I will send you the COMPLETE factory wiring schmatics in PDF form. It covers everything from headlight to tail light, cruise control to CAS.

 

[BadVr4]

the car starts, and runs. my fuel pressure gauge reads 0. fuel pump doesn't prime before the car starts anymore

 

Do you have another relay you can swap in there?

 

[BadVr4]

i dont, i am pretty sure the mpi relay is behind the glove box, anybody have a pic of exactly where its located?

 

[belize1334]

Did the appearance of this problem coincide with the installation of the AEM EMS? If so it could be that the EMS is failing to trigger the fuel pump after it is primed. This was the case on my friends st185 when he was using an EMS for the st205.

 

[BadVr4]

nope, i drove the car around many times without a problem with the ems. it happened when i went to install my boost gauge, after i started it to see if it was working.

 

[BadVr4]

mpi relay? anyone have pics?

 

[Brianawd]

So does the car start and run but then dies? Or does the car start and run but shows no fuel pressure? Is your fuel pressure gauge electric or mechanical? I ask because in one of you post you said it starts and runs but did not say if it dies, but your first post you said it starts and runs but then dies. What is it

 

[BadVr4]

the first time it started and dies. now the car starts and runs fine. my fuel pressure gauge is a mechanical liquid filled one that is on my aermotive regulator