01 lb7 320,000 miles on it has been hard to start last 1500-2000 miles, will not start without ether, if i start it on ether then shut it right off then start it right back up it will fire let it set for more than 10 sec and it will not build rail pressure over 1200, it has a lift pump on it just changed fuel filter, checked the cp3 its not returning hardly any fuel, injector balance rates look good, they are not returning any fuel. i shimmed the fprv today so thats not the problem. only time i can get over 1200 psi is with the ficm unplugged. There doesnt appear to be any fuel in oil truck idles and runs great once it starts, also it has a lift pump so im thinking its not a low pressure side issue? I commanded 23,000psi rail pressure while idle and it wont get past 10500. im out of ideas and about ready to order a new cp3 any thoughts? thanks

 

sounds like you have it pretty much narrowed down but the injectors could still be causing part of the problem from having high return rates but thats not an easy test to run in the truck and the dealers get around $400 to run it, so if it were me i would pull the injectors and have them tested before i bought a pump, but at 0 load and it not holding rail pressure then i belive your probably right on the cp3 being bad

 

yea im thinking with 320,000 miles the pump probably isnt in the best shape anyhow, im thinking i will hope its the pump and replace it.

 

yeah fair chance it is probably not in great shape

 

i know next to squat about dmax's but if you unplugged the ficm and it worked could it be getting bad info from a sensor but not causing dtc's? if it still works with the module unplugged it obviously has open loop/limp dick mode. i know international heui engines will still run with out a injection control (oil) pressure signal but it gives it full pressure so it will stay running. i wonder if it thinks the fuel rail pressure is too high so it cuts it back when its just measureing the pressure wrong, and then when you unplug the module it goes "ah crap i just got a labotamy i better give it full fuel".

 

it would not run. with the ficm unplugged

 

with a worn cp3 and a lift pump i would still think that it could still build enough psi to start. on my lb7 the lift pump will double the idle psi

if the cp3 is hardly returning any fuel then it is pushing it all to the injectors. you could check the fuel return line at the rear diver side of the engine to see if there is excessive return for free, this wont tell you what injector or bank it is but can help you determine if it is injector related.

how many miles on those injectors?

also if your batteries are week it may not be turning over properly, ie low cranking rpm, too low voltage while cranking preventing FICM from running, etc. remember the slower the engine cranks the lower the psi will be do to the cp3 being driven off of the engine. this would be in easy fix if it was