I just bought an 02 duramax and have been going over this thing with a fine tooth comb after having my beloved cummins totalled by a dumb 17yr old kid hitting me . So I came across this chevy and I've always been a chevy guy and the price was unbelievable. I changed the fuel filter and everything was good the whole day. I got up to head to work and she fired up and about 5 sec later it died and would not restart. I tried priming the pump and even put all new seals in it and it still I cannot get the primer to get hard. I finally got the truck to start Withe starting fluid which I know is not good buuuuuttt it rules out some things and gets you going in a pinch. So far today it's been starting. I have noticed that my rail press won't get over 15k and it gets up that high as I'm letting off the throttle. What I'm wondering is how to decifer if it's the relief valve, cp3 or filter head. I have no signs of injectors being at fault, truck runs great and has always fired up strongly. It even fired up strong this morning and just died like the fuel was shut off.

 

Sounds like you need to do the bottle/return rate test. Injectors that run fine may still have a high return rate and make it hard for the cp3 to keep up. This is especially apparent while cranking as the cp3 is engine driven and when rpms are low so is output. This also brings up the batteries. Does your engine crank over quickly?

While the true return rate test on the LB7 is difficult as the injectors are under the valve covers, one can relitively easily test the banks of injectors on eash side

The pressure relief valve on the LB7 rarely has issues, so I would look at the cp33 and injectors

Have you verified the filter head is not leaking air by using a clear hose on the output?

 

It's been firing up with no issues so far. I did replace all the primer o rings and cleaned it out really good, still couldn't get it to get hard. Batteries are fine and truck turns over without issue. It's something in the fuel system. Since pressure increases after the throttle is letting off I believe it's a cp3 issue. I have no there indication that the injectors have any issues. Zero smoke even at cold cold start ups, I have noticed a slight surge in idle and it will hold 10k fairly good unless I really get into it and it will drop. When I let off pressure will shoot up to 15-17k briefly. Just wasn't sure if the d max had anything else in the system to cause a bleed off. I'm pretty familiar with the common rail injection system, I've done alot with the cummins trucks. Didn't know if they used anything extra in the system that cummins didn't use that might be causing a bleed off problem. I guess I'll get a new cp3 ordered and see what kind of power this thing can make. I thought it ran pretty good now, but I drive like a grandpa anyway. I just bought the truck so I'll spend the 500 bucks just to have piece of mind that it's new anyway and won't fail on me when I least expect. Thank you for your help. I'm deff going to try to do a left and right bank return test while I'm there. Only thing I'm worries about is replacing the cp3 and giving the correct pressure and then I have injector issues. I guess we will see. Thank you

 

Only thing I'm concerned about is, it looks like previous owner glued the heater plug wire on top of the filter housing and the fuse was pulled. I'll still grab some clear line and see what it's doing. I'd like to just get rid of the filter head amd put a lift pump on it.

 

Also I pulled the intake heater and drilled and tapped it for my boost gauge, how can I get it to not set the engine light ?

 

The only way i know of is turning off the codes with Efi Live

I imagine that you can rig up a resistor in place of the grid heater but dont know how much higher then the resistance of the stock element you can go before the light comes on. If you have to use a low ohm resistor then your better off with efi live as the heat build up will require a really large resistor

 

Nu2cummins , you get it to hold prime yet?

 

It has never not held its prime, it's always started fine. Although the pump on the filter will not get hard no matter what. Kind of weird. Not sure if it has something to do with the low rail pressure issue but still no codes no real driveability issues other than low power when getting on it. Always starts cold or hot, no extended crank time, no smoke, I unplugged the FCA and it didn't do anything. The fca will stop at 43mpa when commanded with tech 2 you can command all the way up to 100 mpa but won't get actual over 43mpa. All balance rates were 0-3 except number 6 and 8 were around 5-6 positive. Next step is return test on the pump If it's OK then I guess I'm doing injectors. Somethings not allowing the rail to hold pressure. No leaks anywhere I can find so either the pump can't make the pressure or the injectors are returning too much.

 

Nu2cummins, Try to plug the return line on pump and see if the primer gets hard .
6 and 8 are high but you should still get a hard prime at least for a while. I just found my problem . Mine would prime but lose it in about 30 seconds then stall . I don't have a scanner yet that will do the test for me . Here is what i did so far. Changed fuel filter and head , changed fuel pressure regulator and fuel pressure valve . Still wouldn't hold prime . Put dye in fuel and found one return leak on injector fixed that.
I blocked off fuel going to engine on fuel filter head and primed and it held pressure. So that told me that was good. next i took off fuel pressure line from pump and pumped up primer and it held so that tells me the injectors was not causing the prime lose. So i unplugged the return on the pump and when i pumped it up fuel shot out of there. that line returns straight to the tank . So my check valve in pump is bad. Its leaking and causing it to lose prime. So i took it out and ordering a new pump Monday. Mine started out like yours did lose of power when you get on it then it died and wouldn't start . Some one put a lift pump on it and that's what kept it going for a while until the pump finely gave up. Not sure if that's your prob but i would check.

 

One other thing , do you have a lift pump on yours ?