i have had my 94 3.4L since new, and had my fair share of fuel issues. please check the wires at the relay under the drivers side foot rest. i have had numerous issued with it in the past. you need to check the connections at the relay mine got hot and melted at one point during ownership. might just be a bad relay.

 

I changed the relay but it didn't help. The relay wires seem good, but could have an issue further down the wiring I suppose.

Hoping that this issue is something away from the fuel tank (not a dud new fuel pump), I went ahead and put the tank back up and put the exhaust back on the car. Still low pressure, but I was able to build the pressure with a couple key turns and start the car. It runs, but fuel pressure is low at about 38 psi.

 

I did some checking/back probed the electrical connector to the pump. I'm getting a little over 11V when turning the key or putting 12V to the prime connector. When I start and run the car, it's a consistent 12.8V to the pump while running.

 

38 at an idle is pretty normal, it should rise and fall when rpms go up and down.

 

If I'm getting good voltage to the pump, 12V+, when the car is running, does that eliminate any kind of wiring issue as the problem here? Plus the prime connector and just turning the key are a (lower) but consistent voltage as well.

I mean, the pump has good power and gets up to operating psi and starts. But I'm still low before starting the engine and not holding pressure with the car off consistently. The car isn't holding pressure very long after the engine is stopped either. Still maybe a leaking injector lowering psi & draining pressure back to zero?

 

common issue is the one way valve on the fuel pumps not sealing and allowing the pressure to feed back into the tank. yep even new pumps. mine does drop even after all the new stuff I put on it. it does hold better than it did after I went through so many new fuel pressure regulators. mine is a lt1 so not sure the 3.4 has the same issue with the fpr.

 

If I understand this right if you jump 12v to the pump the car runs fine?

To check for a drop in voltage you need to do a voltage drop test. I would start as close to the pump as you can get and follow it back. You can do the same test on the ground but it may be easier to just make a jumper to ground to have double check that is not an issue.

To do a voltage drop test you just need to hook the power side of a volt meter to power at the pump and the negative side to the power side of the battery. When everything ts working right you will get near zero voltage. but if there is a voltage drop you will see a volt number.

 

Like I've said this is the (2nd) new pump, and that's not great that new parts can have problems like this. Would a bad check valve cause the very low pressure I have on key turn though? If it was a leaking injector, do any shops typically have the ability to test those, or do they have to be sent off to one of the injector focused places?

Thanks for all the help on this.

 

injector shop should be able to flow test and clean and tell you if any are leaking or not spraying correctly. on my 3.8 4 of the 6 were not working correctly so I picked up a set of used rebuilds that were cleaned and flow tested for very good price.

 

I did a drop test between the pump to body connector and battery. I got .79V on the power side, and .11 on the ground side. So, some resistance on the power side of things, and that might explain why using the prime connector or turning the key are both measuring at 11ish volts at the pump connector.