With 250k miles, you are at the usual end of life for the CP3. If your balance rates are fine, then you need to do a return rate test. If your injectors check out ok during the return rate test, then that would leave you with a bad CP3. Is the truck hard to start when it has warmed up? Does it smoke at warm idle?

 

With 250k miles, you are at the usual end of life for the CP3. If your balance rates are fine, then you need to do a return rate test. If your injectors check out ok during the return rate test, then that would leave you with a bad CP3. Is the truck hard to start when it has warmed up? Does it smoke at warm idle?

I don't think that is the norm. My truck has over 451k miles and the CP3 has never been touched. I have replaced my FPR once.

 

Starts fine when hot lidles fine, smokes when you mat it but thats when my rail presser comes in to account im assuming beacuse im only making 7kpsi tops and when i let off spikes to 10kpsi

 

Maybe normal isn't the correct word. I'll just stick to saying that it isn't uncommon at those miles. http://www.dieselplace.com/forum/63...gm-diesel-engines/7-duramax-first-generation-2001-2004-lb7/383981-weak-cp3.html. http://www.dieselplace.com/forum/63...max-first-generation-2001-2004-lb7/454692-po93-code-when-pulling-trailer-2.html http://www.dieselplace.com/forum/63...max-first-generation-2001-2004-lb7/457121-replaced-cp3-solved-all-problems.html
There are plenty more but I'm on my phone and copying and pasting just isn't worth it. At 451k, you are only one of the two that I know of, that have surpassed 300k on the original CP3 on an LB7. I'm not saying plenty more people haven't got that many on the original CP3, I'm just saying it wouldn't be impossible, or even rare, for his CP3 to have given up at his mileage. One thing I did forget to mention, is that there are several rubber fuels lines, that if they are collapsing during high fuel demand, can cause the exact same symptoms and not cost any near the amount of money that a CP3 cost.

 

Thanks for your help man i ended up ordering a new CP3 but ill definatly have a look for the lines i checked the ones off the primer and all the ones that i could easly see and get at but definatly worth looking again

 

well it seems that the failure rate for CP3 are higher for the 2001-2002 trucks. Seems odd that it is but I started looking at the sigs of the ones complaining and most were 2002 year model years. Very strange

 

Now that you mention it, I went back and looked at the other person(Charlie B) who made it over 300k on his original CP3, and he has an 04. He might still be going on the original. I haven't seen him post anything about it in a while. You might be on to something with the 01-02 having an earlier failure of the original CP3.

 

Wont start

I have a 2004 duramax and i cannot get it to start. went to start it the other day and it started and died after about 5 seconds of running. Ever since it refuses to start and just cranks. it has battery power, recently replaced fuel filter, and 240k miles on it. anyway to diagnose if its a cp3 or other fuel related issue?
Thanks

 

Very seldom is it CP3 related. The CP3 tends to either work or not and when it's not, it tends to either leak or destruct.


IF the truck has adequate fuel supply to the CP3 and does not start it is quite often injector related. Many a Cp3 has been replaced as a misdiagnosis.


I would start by working the hand pump until firm (or better yet add a lift pump) and see if it will start. If the filter is one of the plastic jobbers chuck it for a good one.


Next step is one that I take very cautiously in recommending. A little sniff of ether is sometimes all it takes. If this is the case it is likely an injector return rate issue.

 

So, my '08 with 168,000 is throwing p0087 codes and change filter messages whenever I'm over 2000 rpm, I can't get rail pressure over 7.6k under WOT. I did a shim kit, and new filter, now I'm replacing the worn and potentially collapsing fuel lines. If this doesn't work I'll be moving on to the cp3 and the fpr. The truck had plenty of power for a while but would tell me to change filter pretty often, then all of the sudden it started falling on its face and throwing the p0087 and reduced power mode. Hopefully it's collapsed lines, not looking forward to buying a cp3.

 

P0087 Fuel Rail Pressure Too Low
See Enhanced Injector Return Flow Test above also.

1) Excessive restriction, fuel supply, plugged filter or sucking air. Install special tool J44638 to check vacuum restriction on fuel supply to the high pressure pump. Maximum restriction at WOT (wide open throttle) is 5 inches HG in park. 2) When driving under hard acceleration maximum would be 7-8 inches Hg. If too high replace the fuel filter and retest.
3) Check the fuel lines on the drivers side valve cover and between the transmission and frame for kinking.
4) If restriction is only a couple of inches vacuum, that could indicate that the fuel supply system is sucking air, use clear fuel lines at the filter head to check for air.
5) Rail pressure should read 1-1.8 MPa with key on and engine off. If out of range replace the rail pressure sensor.
6) Check fuel return from the high pressure limit valve or fuel pressure relief valve. If it is leaking then it will need to be replaced. We have also heard of race plugs leaking, even if you have a race plug, you may want to check for leakage at max rail pressure.
7) With the engine up to operating temperature, use the scan tool to command rail pressure to 21,000 PSI, if the rail pressure will not achieve 21,000 PSI at idle you most likely have a problem with the injectors, Especially if you are having a hard start, miss, rough run or smoke and balance rates are excessive. Perform the enhanced injector return test.
8) Disconnect the fuel rail pressure sensor the fuel pressure should be greater than 175 MPa as displayed on the scan tool.
If these codes set only on hard acceleration or when pulling a hill with a load, check fuel supply issues first. Then see if rail pressure will reach 21,000 PSI at idle, if it does then the low rail pressure under a heavy load is usually caused by a bad high pressure pump.