[Cherry_LLy]

Hi all, I’ve got an 05 that limps. When I bought the thing in December it limped, and its got a new set of injectors and a new cp3 (under my ownership). My questioning is of the lift pump. The truck works mostly fine around town, I can’t do more than 75 without sending it into limp mode because of fuel pressure, but when you hook a trailer to it it’s curtains, goes into limp when you’re on the on ramp to the freeway. I’m looking at the ppe lift pump thinking that’s the culprit because I honestly don’t know what else it would be, I’ve heard they’re pretty prone to failure and a friend of a friend had one fail with the same symptoms as me. Any advice would be appreciated, thank you in advance.

 

[scottydl]

Does your fuel filter head keep its prime over time, or do you ever have to pump the top button a few times to keep it (the button) feeling solid? It sounds like you could have weak fuel pressure making it up to the front, and that could be from an air leak somewhere in the incoming fuel lines or filter head assembly.

Are you talking about lift pumps being “prone to failure”? I was under the impression that these trucks don’t have one from the factory, so there’s nothing there to fail (yet) unless an aftermarket one was previously installed.

 

[ChevyTech77]

Sounds like it’s pulling air in, or has a restriction somewhere, on the supply side of the fuel system. If you think the lift pump is the culprit bypass it and see what happens. Truck should be able to run fine without it. If it still has the factory fuel filter head, bypass that and test it too. They are known to develop issues and pull air over time.

 

[mray]

Pull the bleeder screw and turn truck to on and see if fuel pump pumps fuel out.

 

[Cherry_LLy]

Sounds like it’s pulling air in, or has a restriction somewhere, on the supply side of the fuel system. If you think the lift pump is the culprit bypass it and see what happens. Truck should be able to run fine without it. If it still has the factory fuel filter head, bypass that and test it too. They are known to develop issues and pull air over time.

I just replaced the fuel filter head in January, along with a new filter since it was losing its prime. It has a ppe lift pump from the previous owner and I’ve heard they can kick the bucket pretty soon since they’re not at the same level as the Fass or air dog kits. I’ll bypass the pump and get back to you.

 

[Cherry_LLy]

Does your fuel filter head keep its prime over time, or do you ever have to pump the top button a few times to keep it (the button) feeling solid? It sounds like you could have weak fuel pressure making it up to the front, and that could be from an air leak somewhere in the incoming fuel lines or filter head assembly.

Are you talking about lift pumps being “prone to failure”? I was under the impression that these trucks don’t have one from the factory, so there’s nothing there to fail (yet) unless an aftermarket one was previously installed.

There’s an aftermarket one from ppe on it, and I feel like it’s got an air leak or something but I’m not sure. As far as I know the filter head doesn’t lose prime, but I will check it and see what I can see.

 

[Cherry_LLy]

Update: I bypassed the lift pump but it’s still limping. Doesn’t lose prime, so I’m thinking it’s a high pressure leak? Or maybe the sensor that detects rail pressure is bad??? I’m kinda shooting blanks here so any advice would be great

 

[ChevyTech77]

Update: I bypassed the lift pump but it’s still limping. Doesn’t lose prime, so I’m thinking it’s a high pressure leak? Or maybe the sensor that detects rail pressure is bad??? I’m kinda shooting blanks here so any advice would be great

Did you bypass the filter head?

 

[Zsams1988]

I had a old head give my all kinds of issues rebuilt it no luck got a new one with a new metal beeder screw

 

[Cherry_LLy]

Did you bypass the filter head?

I didn’t but I could try that. I feel like it’s not the filter since it’s practically brand new, and the truck still won’t go above 17k rail pressure, which is what it would do from the day I bought it with the old filter

 

[Ron Nielson]

Did you do what post #4 said? Do you ever have any codes from this problem? What are they? I would think that if your fuel pressure never went over 17K, you would have a code or two.

The CP3 pump always creates full pressure, 20K+. The FPR (fuel pressure regulator) mounted on the top of the CP3 is a solenoid, regulated by the ECM, that limits the fuel pressure allowed beyond that point in the fuel rail. The fuel rail pressure sensor tells the ECM what the pressure is in the fuel rail. Then ECM uses that information to adjust the fuel rail pressure via the FPR. The ECM has a lot of inputs to determine what the desired fuel rail pressure should be. If you were to detach the connector at the FRP, the full pressure output of the CP3 should be sent to the fuel rail and the fuel rail pressure sensor should see 20K+ pressure.

 

[Cherry_LLy]

Did you do what post #4 said? Do you ever have any codes from this problem? What are they? I would think that if your fuel pressure never went over 17K, you would have a code or two.

The CP3 pump always creates full pressure, 20K+. The FPR (fuel pressure regulator) mounted on the top of the CP3 is a solenoid, regulated by the ECM, that limits the fuel pressure allowed beyond that point in the fuel rail. The fuel rail pressure sensor tells the ECM what the pressure is in the fuel rail. Then ECM uses that information to adjust the fuel rail pressure via the FPR. The ECM has a lot of inputs to determine what the desired fuel rail pressure should be. If you were to detach the connector at the FRP, the full pressure output of the CP3 should be sent to the fuel rail and the fuel rail pressure sensor should see 20K+ pressure.

It doesn’t throw a code which I think is strange, but I feel like it has to be electronic since all the bigger mechanical bits are in order. Are you saying I should disconnect the fuel rail pressure sensor and see if it fixes it?

 

[mray]

If you disconnect the fuel rail pressure regulator that is on the CP3 pump and it maxes out at over 20,000 psi than that should rule out that the CP3 pump is bad. Could be injectors returning too much fuel, might try a return rate test on them if you haven’t already. There is information on here about performing this test.

 

[rknuesel]

Check your fuel rail pressure relief valve. Better yet just install a race valve an get rid of the valve all together!

 

[Cherry_LLy]

Check your fuel rail pressure relief valve. Better yet just install a race valve an get rid of the valve all together!

Rail is already plugged

 

[Cherry_LLy]

Spose I should update y’all on the status. Brought it to a shop to flash it back to the stock tune since it kept booting my computer, they got it back to stock but now it smokes like hell and it also isn’t fixed. Maybe the injectors need to be calibrated?? Shooting in the dark at this point.

 

[Ron Nielson]

Are you saying I should disconnect the fuel rail pressure sensor and see if it fixes it?

No. I don't know what would happen (except a DTC being thrown) if the FRPS was disconnected. You could try and see what happens. See if you find something here: Chevrolet-GMC Diesel Diagnostics