Actual rail pressure is 300 psi lower than desired. Is the pump bad, or is it the regulator?

What kind of tuning do you have? The PCM might be asking for more fuel than the rail's relief valve can hold. I'd check that first if you've done any fuel mods, then look at the regulator. Pump should be good.

i would look at your relief plug first, as already stated because your pump is still supplying you pressure, but it is most likely not able to keep up if your relief is dumping the fuel to return. that will be the cheapest and easist thing to go after first

I know the pump is good, got a ton of fuel via return line. There is a pressure relief on the back of drvr side fuel rail, and a connector righ where the return line to the tank is joined into rail. is that another valve, or just a sensor?

what make and model do u have?

I know the pump is good, got a ton of fuel via return line. There is a pressure relief on the back of drvr side fuel rail, and a connector righ where the return line to the tank is joined into rail. is that another valve, or just a sensor?

It's not another valve. The relief valve is an 18mm hex head on the end of the rail. It's difficult to see without the glow plug controller taken off.

do a search for FPRV, tons a info. The hand of god tightens the fprv into the back of the fuel rail, towards the firewall. You can shim it, or put in a race valve that completely blocks it off. I have a race valve because the stock fprv was mangled when the fellas at fleece got it out!!

What tune are you running, maybe you need a lift pump. Might be that you are just demanding more than the cp3 can supply without help.

do a search for FPRV, tons a info. The hand of god tightens the fprv into the back of the fuel rail, towards the firewall. You can shim it, or put in a race valve that completely blocks it off. I have a race valve because the stock fprv was mangled when the fellas at fleece got it out!!

No kidding. Those things are put in there with the impact wrench from hell. I successfully removed all six corners on one before I got it out.

What tune are you running, maybe you need a lift pump. Might be that you are just demanding more than the cp3 can supply without help.

Good point. You might try running a high-perf pickup or a straight suction line out of the fuel tank and bypass the stock pickup unit, too. Might also be time to mod the CP3.

300 psi difference between actual and commanded is nothing to worry about........

300 psi difference between actual and commanded is nothing to worry about........

I agree, 300psi less is only 1.2% below normal. Does not seem significant to me.

300 psi difference between actual and commanded is nothing to worry about........
:exactly: