need some help

D Twigg

D Twigg

Starting to understand
Joined
Jul 17, 2008
Messages
665
I have a buddy that has a 02 3500 cclb drw 4x4 with intake exhaust and a efi autocal spade and our '99 6.5 dually at work is faster than it :nail:. Problem is when you run it WOT it takes off and then falls right on its face. Took a couple data logs and sent them to duramax tuner and they said that it was only getting about 3k-5k psi of rail pressure instead of the demanded psi. Question is, is the cp3 gone out or is there something else we should be looking at. Fuel filter has about 3000 miles on it and that didn't help any at all. Thanks in advanced for any help.

Twigg
 
Check codes.
Probably rail pressure regulator needs shims or race plug or fuel filter or..........Check codes
 
Sorry forgot to mention trucks not throwing codes and it's been doing this even with the new fuel filter.
 
It should be setting low rail psi codes if its that low. Could be bad cp3, bad injectors, or air on the supply side
 
It will only set a low rail code if Duramax tuner left it enabled. Best option is to return it to stock, and diagnose from there. Maybe a collapsed fuel line??? Does it have a lift pump?

Also LB7s hardly ever have issues with the relief valve kicking open.
 
How many miles on the truck? How many miles on the injectors? Check for fuel in the oil. Basic LB7 shenanigans.

Does it start hard?

Like stated, turn it back to stock and diagnose from there.


I would find it hard to believe that Dmax tuner would shut the Low rail pressure code off, and its been my experience that they don't.
 
Truck has 185k on it. As far as we know the injectors and cp3 on truck are stock. Truck does not have a problem starting and does not have a left pump. It is not mixing fuel in the oil. I know nothing about these duramax's. Tomorrow after work I'll return it to stock and look at all the fuel lines.
 
When my truck's rail pressure was low it didn't trip codes, just ran like it had no nuts after 8 new injectors. Ended up doing a LBZ pump since it cost less and Rob's tuning.
 
D Twigg said:
Truck has 185k on it. As far as we know the injectors and cp3 on truck are stock. Truck does not have a problem starting and does not have a left pump. It is not mixing fuel in the oil. I know nothing about these duramax's. Tomorrow after work I'll return it to stock and look at all the fuel lines.
Click to expand...


Here is a good write up on how to check injector health with a Scan tool. Keep in mind that there is no surefire substitute for measuring the return rates with a bottle test.

http://www.dieselplace.com/forum/63-gm-diesel-engines/7-duramax-first-generation-2001-2004-lb7/576505-proper-way-check-balance-rates.html
 
I would check the fuel lines i have seen them collapse.there is multiple rubber hose sections most common is by the steering column and between the transmission and the frame on the drivers side. Also just try leaving the gas cap off in case it's not venting
 
You must log in or register to reply here.
Back
Top