According to a print out(From a 6600 duramax engines theory and diagnostic handbook printed in 2006) the service manager at dealer gave me "If the fuel rail pressure is too high,the pressure control valve's pulse width modulation increases to limit the flow of supply pump fuel to the high pressure pump.Excess fuel is directed to lubricate the high pressure pump,recycled to the supply pump and eventually directed to the return line." Wouldn't that mean if the valve was stuck it would all be rerouted to return? I only ask because ive been confused with this whole process as i have 0! background in anything to do with diesels or engine mechanical of any kind. Ive rebuilt a wrecked truck once a few years ago but body work is as far as i go. I will be home shortly and will be trying my ecm with the used regulator.
Dmax Guru Needed EMERGENCY HELP!!!(Master dmax techs or pros please)
- Thread starter 07DuallyDmax
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The FPRV does NOTHING to return fuel. All it does is limit how much fuel is feed into the pistons of the CP3 byt the supply pump of the CP3. As it sends MORE current, the coil inside the FPRV pulls a valve inward and blocks off incoming fuel, less current lets the valve out and more fuel flows. No current and it goes wide open full feed. And if you were measuring MV then you are checking voltage NOT amperage. And amperage is what you have to measure. And no clamp on meter is accurate enough to measure milliamps accurately.
Leave the friggen FPRV valve out, hold your finger over the FPRV hole in the CP3, have somebody turn the truck over. If fuel comes out the high side line now, then you had a blocked FPRV, if not then your CP3 is junk.
Leave the friggen FPRV valve out, hold your finger over the FPRV hole in the CP3, have somebody turn the truck over. If fuel comes out the high side line now, then you had a blocked FPRV, if not then your CP3 is junk.
Where is that fuel flow going if its not returning it? And an update with where we are at with the truck. I got the ok to plug the used regulator into the ecm to see what happens.We started the truck and left it ran several times with the regulator unplugged and to see if we could duplicate the fault we plugged it in and sure enough now the truck wont start. Now this regulator is making the EXACT same noise the new one we just pulled was making.We quick unplugged it and now the truck starts again.
The diagram you posted shows where it goes: nowhere. It just stops flowing. Since you have a lift pump, the lift pump will raise the fuel line to max pressure (usually 7-15 PSI) then its regulator will return fuel to the tank.
Since it runs with the regulator unplugged, but not with it plugged in, you can now safely diagnosing an electrical issue.
Now you can get your scan tool back out. You want to log the following parameters (they may be called something else with your tool):
- RPM (Engine RPM)
- FRPCOM (Fuel Rail Pressure Regulator Commanded)
- FRPCOMM (Commanded Fuel Rail Pressure Regulator Flow)
- FRP_C (Fuel Rail Pressure)
- FRPDES (Desired Fuel Rail Pressure)
Look at what the ECU thinks it is doing. At this point, I would be trying to narrow down the issue to one of these:
- Wiring problem (short to power or ground - diagnose this with an ohm meter)
- Tune problem (ECU is commanding too much current - have someone look at the tune file)
- ECU problem (ECU is commanding normal current, but providing lots - replace ECU)
Good luck.
Edit: My manuals don't go up to the LBZ, but the regulator electrically is the same for all years. If you are going to test the wiring harness, here are what the pins do:
Pin 1 - Connects to ECU to get power. Power should be steady on with key on.
Pin 2 - Connects to ECU to ground to PWM the regulator. Should vary in voltage relative to ground.
Pin 3 - Always connects to ground.
There should be no continuity between any of those pins on the harness with the key off. If there is, there is a short.
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Louder than the lift pump? only thing i can compare it to is it sounding like a banjo being plucked on one string and it holds that sound for about 3 seconds than gets quite.
as of now we are going back over the electrical side of things with the info "DAVe3283" has just gave us.
The regulator is only 2 wires, not 3. My diagram shows an ECM supplied voltage supply, and then a PWM ground to control current flow.
Yes, the regulator can buzz very loudly.
I seem to recall mine being only 2 pins too. This is the diagram from Techline for a 2005 LLY:
I took it to mean the 3rd wire is in the harness, but not connected to the regulator. Maybe that wire in the harness is shorting to the PWM ground, causing it to increase the duty cycle? Or maybe GM's diagram is on crack (wouldn't be the first time).
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It's a shielding wire. If you look at the diagram it says the wire is bare and at the connector it says "not used". The LLY and up trucks have a little jumper harness that has a 3 wire connector at the top of the y-bridge neck that runs down to a 2 wire connector at the regulator.