LB7: Diagnosing Loss of Power Bad CP3?

[niteflite1287]

Looking for some opinions on plan of action before I try and pull this off since I'm relatively new to the world of diesels.
Problem:
Truck has relativity poor power, gotten worse since I've owned it. Its especially bad on hills, I can get her going up to highway speed (75 or so) on flat ground if i'm gentle on the pedal and slowly work up to speed at around 2100rpm or so, however on decently steep hills she get very unhappy and down shifts to what I'm guessing is second or third and the rpm shoots to over 3000 and the truck slows to 55mph. Fuel mileage is also poor and getting worse around 10-11 now. Clearly something isn't right.

Diagnosis:
So far I've replaced the fuel filter with it getting marginally better, and check the OBDII with a scanner and pulled the P1093/P1094 codes. Unfortunately this thing cant read fuel rail pressure. I'm guessing from the reading I've done that it is a bad CP3 but want to verify that before I shell out the cash to upgrade it. I'm tempted to purchase a PPE fuel rail pressure gauge and install it and then unplug the FPR and check the pressure. (Part of me thinks this is great justification to purchase the egt and boost gauges I've had my eyes on). However, I am wondering if this would still leave the possibility of bad injectors open or some other problem. Basically, what else should I do to diagnose my LB7 or should I just find professional help. Wonder how much it would cost to have Ben diagnose the problem for me? (living in CT for the next 5 months)

 

[MaxPowerLB7]

I hate to be the bearer of bad news, but more than likely you need new injectors. It'd be a good idea to log rail pressure though.

 

[SHOTZY]

I hate to be the bearer of bad news, but more than likely you need new injectors. It'd be a good idea to log rail pressure though.

Think your right. Unfortunately the only way to know for sure is to do a fuel return quantity test. This can be a big PITA if you've never done it and you need a kit from gm also. Usually the dealer performs this test. What year is your truck? Miles? If it's an 03 bought after June 12 or newer and have under 200,000 your coverd under warranty for injectors. Don't know if this helps, good luck.

 

[niteflite1287]

Maybe someone wit some GM warranty knowledge can advise me. The truck itself is an 02 with 225000 on it, hover the motor was replaced (by a dealer) 3 years ago and has somewhere near 50000 on it.

 

[SHOTZY]

Sorry bro, its outta warranty. Hopefully its the pump. There's a slight chance it could be the fuel return valve. This would be found during the return test.

 

[S Phinney]

I would drop the fuel rank and clean it and the basket pickup. It may not need it but the loss of power like you explained can happen when the pickup is restricted. It can be checked from the vacuum port on the front passengers side valve cover beside the alternator. This should not read more than 2-3lbs of vacuum if you are not running a lift pump. If it is more then check for restrictions. There is also a problem with the fuel line collapsing on the braided part beside your trans. Where it changes from metal to braided and then back to metal at the bend it will collapse and restrict fuel. hope this helps you find the problem.

 

[niteflite1287]

Thanks for the advice. I dropped the tank 6 months back and replaced the fuel sender, I'll check the fuel vacuum pressure that out as soon as I get back to my truck...which may be anywhere from 1-6 weeks from now...