hi,im new to deisel bombers and am looking for some input.i have a 01 duramax that wont pick up or return fuel.it will start and run as long as you keep pumping the primer,idles good sounds good and no exessive smoke...but wont pump fuel on its own.330000 miles on truck,heres what has been done so far,new injectors 30000 miles ago,ive just replaced the fuel pick up,put in lift pump,new filter owsing then new cp3,changed fuel lines pick up and return and still wont pick up fuel.now the kicker... ive put a scan tool on it butthere is nothing,not only no codes but wont even light up the scan toolmight i have a dead ecm?????a big thanks for any help

 

Power to scanner on all OBDII brands is tied into cig lighter fuse. Where did injectors come from? Rare for PCM failures, but if engine runs while pumping primer, my guess it's fine. Check cig lighter fuse & replace, try to run scan for codes again.

 

cig liter fuse blown...nice call!!!got output shaft speed sensor circut-no signal and fuel rail presure low[probably due to the output sensor problem ?]ill check out the output shat sensor and wireing an see what i come up with

 

just occured to me the speed sensor is meaning th trany speed sensor,so back to the low fuel rail pres. i dont know where the injectors were purchaced as they were replced just befor i bout the truck.i put clear hose befor and after the fuel filter to look for air and then disconected th fuel line at th drivers side valve cover and ran them into a jug so i can see if its picking up fuel and returning fuel.it does neather,only fuel that goes in is from pumping the primer and zero fuel comes out the return

 

All 01 to 03 LB7 engines have injectors and return lines under valve covers & if injectors came from aftermarket parts store, chances are you got same junk as removed. Check oil level and viscosity to make sure not diluted. If overfull, fuel return lines are probably leaking into crankcase due to loose banjo bolts or return line seals not replaced/lost during injector install. GM extended warranty on injectors only to 7 yrs/200K after learning injectors were faulty from Bosch. 03-04 Dodge injectors had identical problem but Cummins nor Bosch will acknowledge. Had customer at my shop who had bought set of injectors from Napa and eventually lost compression in 2 cylinders due to high return rate and if this were problem, you would have heavily aerated return fuel & a lot of it. Did you install CP3? Did new one come with FP regulator? That's the only other guess at this point. They were also large problem on early Dmax. Have you tried putting clear hose on return line? Also fuel rail pressure relief valve could be bad causing bleed off. Don't just throw parts at it.

 

i put the pc3 in,it came with new fp regulator,have clear line on return also,i see that it is returning a very small amount of fuel as i pump the primer.checked oil for dilution and it is free of fuel,i am curios about the fuel rail pres relife valve bleeding off,any way to diagnose it? thanks

 

Relief valve test would require temp test line with hose on it. At this point, am wondering if injectors were replaced at all. What type of lift pump was installed? Dumb question is does truck have dual tanks with 1 fill spout? Is all air bled out of system at CP3 return line? If air is trapped in inj pump, it will never pick up until bled. To test injector return rate, special tools will be needed. Does your scan tool have monitor mode where you can observe rail psi while cranking? Try using air to pressurize tank and loosen all banjo bolts up to CP3 return until no air left. Is pressure regulator harness plugged in all the way. Regulators are normally open and will allow fuel to pass thru with key off. PWM operated when running.