Help please!! Cp4 issues

[dylon333]

Help!!! 2011 lml. Trucks been fluctuating rail pressure. Has a lift pump. Pulled the fpr out of cp4 to check for metal, clean as can be. Reinstalled ran truck for a min. Shut it back down to hook up fuel pressure gauge to make sure lift pump wasn’t acting up, key on engine off pressure was good. Start truck up let it idle a min everything was fine. Went to rev truck up it reved up and died like some one shut it off. Now it will only build 200psi rail pressure.

I’ve pulled fpr #1 back out still no sign of any debris, pulled the return line off for fpr #2 and had zero fuel flowing from left rail while cranking. Pulled injector line to make sure I had fuel there. Tried unplugging rail pressure sensor to make sure it wasn’t shorted and still no start. Also tried unplugging the fpr#1 like the cp3s but still no go. Surely this pump didn’t just shit out on me sitting here did it?! I’ve got to be over looking something? Right!

I’ve also swapped in a new fpr in the cp4 with a new one. Still no start.

Truck ran decent just had the fluctuation rail pressure intermittently. Now it won’t start at all.

I have efi live v2 and snap on solus that I’m using diag to read my live data. Truck has no codes either.

 

[2004LB7]

I seen the high pressure check valve stick open on my VW CP4

It did some weird things with pressure until I got it free

 

[dylon333]

Ok I’ll look into it

 

[coker6365]

Pinch the return line on the injectors ar the rear of the driver valve cover to see of you can get the injectors to fire. Pulling the FCA out just adds chances for debris to fall into the fuel cavity and creates and air pocket.

Did the rail fluctuation suddenly start? Has tuning, hard parts, or anything else been changed?

Sent from my SM-G965U1 using Tapatalk

 

[dylon333]

Ok I’ll try that tonight. Fluctuations on rail pressure started back during the summer, would do it on hot soak starts but would only last few seconds so kept putting it off. Been last week or so it’s been getting worse and does it while driving down the road now all the time. No parts or tuning has been changed. I’ve tried bleeding the system a few times with no luck

 

[coker6365]

Could be a number of things effecting it. Log the pressure relief on the rail and the FCA duty cycle. See if you are seeing any fluctuations. Then I would start on the return side

Sent from my SM-G965U1 using Tapatalk

 

[KyleC4]

You can use the primer pump or lift pump even and key on and see if pressure shows that way on scan tool. Then just crank and see what the max pressure you’ll make is. Make sure crank signal is good with scan tool and see that engine is spinning enough rpm to make pressure. 100rpm is minimum but I think most people can pick up on that if crank speed was a problem. You need around 2000psi rail pressure to fire. I personally have not seen a pressure relief valve pop yet on a lml. Possibility though. Otherwise could be a cp4 depending what you find. Cause I have had some where I’d take the fpr out and see only a single small flake only to find the large amounts of metal got pumped into the rail.

 

[dylon333]

Crank speed is good. Only building 200 psi rail pressure. I’ll pop the #2 regulator from the rail and see what it looks like.

 

[dylon333]

Update. So I got the other regulator out, there definitely some metal shavings on it. So does that mean I need to replace injectors lines rails and every thing? Or since it’s only a little bit can I get away with flushing the rails and put the system saver regulator in it and be ok

 

[Chevy1925]

at min, you are putting a CP4 in. then hopefully nothing reached the injectors and you can just clean the rest of the lines out.

 

[coker6365]

If you are referring to the rail fittings, even a perfectly healthy running system will show signs of debris. Seen it plenty of times.

Sent from my SM-G965U1 using Tapatalk

 

[dylon333]

Good deal. Cp4 is ordered I’ll flush it all out And cross my fingers

 

[coker6365]

Cancel that order. I have 2 brand new GM CP4's on the shelf I will cut you a screaming deal on.

Sent from my SM-G965U1 using Tapatalk

 

[dylon333]

How much

 

[ikeG]

GM part # 12672028 is the pump kit. Includes one cp4, both rails, both regulators, the pressure sensor, and all 8 injectors.

Sent from my SM-G960U using Tapatalk

 

[coker6365]

I have a full GM kit with the rails, injectors, and CP4 kn the shelf as well.

If you want just the CP4, $200 and it's all yours. I have 2 or 3 of them new on the shelf.

Sent from my SM-G965U1 using Tapatalk

 

[coker6365]

GM part # 12672028 is the pump kit. Includes one cp4, both rails, both regulators, the pressure sensor, and all 8 injectors.

Sent from my SM-G960U using Tapatalk

Updated part number is 12702459

Sent from my SM-G965U1 using Tapatalk

 

[ikeG]

Updated part number is 12702459

Sent from my SM-G965U1 using Tapatalk

Thanks. What exactly was updated

Sent from my SM-G960U using Tapatalk

 

[coker6365]

Thanks. What exactly was updated

Sent from my SM-G960U using Tapatalk

Same parts. Just a different part number. Likely just a different supply chain.

Sent from my SM-G965U1 using Tapatalk

 

[KyleC4]

Definitely different supply chain. Price came way down on that kit over the years. Used to be 8-10k for just parts when we first started seeing problems