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Lb7 duramax no start low rail pressure while cranking

Old 04-16-2019, 09:36 AM
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Default Lb7 duramax no start low rail pressure while cranking

Hey guys. New to the forum. Hopefully I post this in the proper page.

So I bought a 2001 duramax that wouldn't start for a great price, been trouble shooting for about a week and can't seem to figure out 100% what's wrong.

I started by installing a fast fuel pump with filters , replaced all the orings and fuel filter in the factory head, New batteries.

When I go to start it it will crank around 180-220 rpm but only build 500-600 psi of rail pressure. I did a return rate test ( with both banks and cp3 still hooked together) I get about 2oz of fuel return 70ml. If I unhook the cp3 and try it I get 25ml from both banks. I did this with the ign 1 Relay unhooked.

I can get it started with some spray, and it runs good. But if I command Max rail pressure at idle will only get about 6-7k psi. The balance rates had injector number 5 showing about 4.5-6 all the others were anything from 0.1-2.2. If I step on the gas I can get the rail pressure up to 23k and the desired Vs actually are always very close.

Even if I try to start the truck with the FPR unplugged it won't make any more than 500-600 psi. Also when I have the return from the CP3 off, hand priming the pump will steady push fuel thru the return of the cp3, I'm not sure if that's a sign of a failing cp3 or maybe it's normal.

I have not tested each injector bank individual since I'm not 100% sure what connections to unhook for that. But 25 ml from both banks seems OK? Average of 3ml per injector

Also when I get the truck running I get no codes at all. Hopefully you guys can give me some advice on what to check!


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