Installed motor won't start - Page 2 - Chevy and GMC Duramax Diesel Forum
01-04.5 LB7 Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

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post #11 of 14 (permalink) Old 07-19-2019, 08:27 AM Thread Starter
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Quote:
Originally Posted by stevewaclo View Post
Iím testing the limits of my LB7 knowledge and encourage old timers to weigh in...please.

To be clear, the engine you now have in the truck has its original fuel system (CP3, lines, injectors, etc) and that engine sat since 2005.

To answer your question about failed return circuits in the injectors, the CP3 provides a high pressure, low volume supply of fuel and even one sketchy ball/seat in one injector would act like a hydraulic short circuit, and rail pressure would not rise to a level necessary for starting. A more likely scenario would be all the injectors may be somewhat comprised, with the same effect on rail pressure.

67,000 km is about 47,000 miles which would put your replacement engine well below the 70k +/- time to failure of typical LB7 injectors, but all the time your replacement engine was on the shelf is worrisome . As you know, diesel fuel has a limited storage life and, just speculating here, but I wonder what evil old fuel could have been doing to the system over all those years?

You mention you can hear fuel returning to the tank.

The return test I suggested only amounts to a quite small amount (? Donít recall the number but mmís) during a 15second crank and it seems unlikely to me there would be enough flow to hear. Where do you hear it?

Seems to me a good test of the CP3 would be to find a gauge of appropriate pressure range and connect it to the CP3 output. Measuring pressure there would seem to eliminate downstream problems. The fact that when you put fuel directly to the CP3 and it immediately came out the return side may be what the police call ďa clueĒ.

Iíll stop rambling now, and wish you the best.

Hereís an LB7 fuel system diagram and an internal view of an injector, showing the return circuit, that may be helpful:
Thank you for the information. I appreciate it. I will find the appropriate gauge and test the pressure coming from the CP3. I understand where you are coming from saying possibly all injectors are faulty but how is it not more likely that one thing failed immediately then 8 things simultaneously. Is there a check valve or relief valve that could be faulty in the CP3? I understand it may end up being injectors but I have a spare cp3 and it would be way easier to change then the injectors so I would like to rule everything out before jumping to injectors. Thank you for your help.
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post #12 of 14 (permalink) Old 07-24-2019, 04:06 PM Thread Starter
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Just to close off this post with a conclusion and fix. It was the injection pump that crapped out. I imagine just from sitting for so long. Runs excellent now with new injection pump.
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post #13 of 14 (permalink) Old 08-04-2019, 09:11 AM
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Thanks for the update.

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post #14 of 14 (permalink) Old 08-06-2019, 03:56 AM
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Originally Posted by tylerearl88 View Post
Just to close off this post with a conclusion and fix. It was the injection pump that crapped out. I imagine just from sitting for so long. Runs excellent now with new injection pump.
Glad that you got it figured out. Lots of great info on this forum.

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