Bama2door

I have a '99 2 door tahoe that I just swapped an '02 LQ4 into from a 2500HD Silverado and am having fuel pressure problems. I have hooked a fuel pressure gauge up to the shrader valve and on startup the pressure peaks to around 50psi and then it will run for about 10-15 seconds and slowly sound like it's gonna die until it shuts off it gets down to 18-20psi. So at this point I thought it was a faulty fuel pump so I replaced that yesterday along with a new fuel filter and new fuel pressure regulator and it still does the same thing. The injectors that came with the motor weren't good so I got some used off a guy who had a LQ9 so I know it's not an injector problem either.

I am so stumped it is making me so mad, I've tried damn near everything and still can't seem to get it. Any ideas or help would be greatly appreciated!

mhotrodscooter

iTrader: (13)

Have you checked voltage going to the pump? Just a thought!

Bama2door

I have a Nelson harness and hooked up my voltmeter from the 87 plug on the fuel pump relay and when I go to start it, it will still read above 12v. My buddy said to run a wire from the 87 plug of relay back to the positive wire on the fuel pump and then run an extra ground wire, any other ideas?

mhotrodscooter

iTrader: (13)

So what your saying the voltage is dropping out going to fuel pump?

Bama2door

I got it figured out. I ran a wire straight from the power wire of fuel pump to the 87 prong of the fuel pump relay then hooked an extra ground wire from the pump and that fixed it. You can see when you take the wire off the 87 prong the pressure starts to drop but as soon as you put it back on it builds pressure again so I guess it wasn't getting enough voltage, thanks for the help man