Fuel pressure problem?

Exgmguy

Exgmguy

Club Member
I am trying to diagnose a lean fuel condition under boost on my turbocharged Jeep. I installed a fuel pressure gauge. I noticed that when I prime the pump, the pressure jumps to about 40 psi like normal but drops back to zero as soon as the pump stops priming.
I am running an FMU. I pinched off the return line coming from the FMU and primed the pump again. It will hold pressure with the return line pinched down.

So I am guessing that the fuel is not bleeding back through the pump, or through a leaky injector. I think it has to be getting by the stock fuel pressure regulator and the FMU.

Any ideas?

Thanks,
Rob
 
I though an FMU is a boost referenced regulator? I think that the fuel system should hold pressure for awhile after pressurized. The lean problem happened out of nowhere, so something happened. Pump took a crap, bad regulator, etc....

The FMU works when I blow into the line, I don't think it is rising under boost though. Footbraking about 2 psi of boost in the driveway has the fuel pressure at 39 psi, just like it was N/A.
 
Thanks for the input. The factory regulator was missing an o-ring, so the fuel was going right around the missing o-ring and back to the tank.
 
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