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Old 01-11-2013, 01:41 PM   #1 (permalink)
jhanratt
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Do You Think I Need A New ECM???

I have a 2003 Chevrolet CC 4X4 Duramax Allison LB7 with 198,000 km on it. It is stock and I have had it since new. The injectors are original. It has been a great truck but it now has a difficult to diagnose issue. The problem started last winter.

When it is cold outside and the truck is warmed to operating temperature it will not restart. It will either crank for an extended period and then start or will sometimes fail to start at all. If you let it sit for a few hours until it cools it will start no problem. Also if you give a shot of ether it will start and run fine. I know this is not healthy for it but when I am stuck in the woods with a dead truck it is an attractive option.

All summer when it is warm outside there was no issue.
Once it starts it runs great. It pulls hard and does not skip a beat. The fuel economy is still great but I can't quote numbers of the top of my head.

I immediately changed the fuel filter. It made no change at all. I did note that the used filter was not full to overflowing like it had been on previous changes.
I ran my code reader and came up with nothing.
I took it to the GM dealer in town. They scanned the fuel injectors and return rates at my request. They stated that all was normal and diagnosed a faulty glow plug relay. I paid for a relay even though I knew it was unrelated. Not surprisingly the new Glow plug relay made no change at all.
I then went to a local mechanic who owns the same truck and will take the time to talk to you in person. He said try priming for a while before starting and see if that makes a difference. I primed until it was hard and started for a while. This also made no change. I also tried bleeding the valve on the fuel rail to check for air. I never did find any air in the fuel rail.
I left the truck with him for three days so he could check it cold warm etc. He checked the injectors and determined they are fine. He found the fuel rail pressure was way low especially when warm. He also checked the fuel pump and determined it is fine. He did find some codes but we did not get in to specifics. He is recommending a new ECM and estimating $3,200.

Any advice?

Thank you all in advance for your help.
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Old 01-11-2013, 08:13 PM   #2 (permalink)
jerkyman65
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My local stealer quoted me $1700 for mine. I foumd a rebuilt one at Nationwide Parts Distributors in Jacksonville, Fl, for $615 shipped 800 833 0386 or a dealer i Frisco, Tx for $1050 plus shipping, 214 472 6803.
Good luck!
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Old 01-11-2013, 08:44 PM   #3 (permalink)
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I'm willing to bet they tested balance rates, not the return rates. What you are describing is normally caused by an injector returning to much fuel to the tank during cranking not allowing it to build enough rail pressure to allow the injectors to pop. When it does this monitor rail pressure. I believe you need about 1700PSI before it will even try to start. If the return rates are within spec and it stil lwon't build rail pressure, then it is most likely a CP3(which is very believeable at your milage). I HIGHLY doubt an ECm would cause your issue as you say it will start and run with a shot ether. And for future reference, NEVER use ether with the glow plugs hooked up. It will cause damage, and could break a glow plug tip off in the cylinder.
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Old 01-11-2013, 08:44 PM   #4 (permalink)
07keo02
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Did they do actual fuel return rates? Pretty extensive on an lb7. Balance rates can show good and still be returning too much fuel. Seems like it is not building the required pressure to re-start. My guess would be injectors first then the cp3.
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Old 01-11-2013, 08:46 PM   #5 (permalink)
07keo02
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Sorry for the similar post must have been posted while I was typing.
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Old 01-11-2013, 09:14 PM   #6 (permalink)
heymccall
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ECM? I'd blame the CP3 long before I'd blame the ECM for the described symptoms.
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Old 01-11-2013, 09:37 PM   #7 (permalink)
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Ecm Is NOT your problem. look into your fuel lines fto filter housing from and all the rubber as well as a leaky fuel housing. cp3 is very crappy at pulling fuel. had this issue with an 04 that the guy nigerian rigged a fuel filter in place of his stocker thinking it was bad. when I replaced his injectors (they were bad) I reuilt his filter housing and replaced all of the rubber and it starts every day all day in any weather. we are now in the single to neg didgets here too
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Old 01-11-2013, 09:53 PM   #8 (permalink)
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Does the LB7 have a FPRV? I know my '06 does and along with many others have had to shim it. May want to install a lift pump to push fuel up to the filter so the CP3 does not have to work so hard to get fuel top the high pressure side of the pump. I would not just throw an ECM at it and hope for the best, it sounds like a fuel related problem for sure.
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Old 01-11-2013, 09:55 PM   #9 (permalink)
heymccall
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An FPRV problem would show up as a rail pressure issue under load, too. Not just at startup. Actually, both FPRV failures I've had here weren't hard starters, by any means. They just limped under load.
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Last edited by heymccall; 01-11-2013 at 09:57 PM.
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Old 01-11-2013, 10:07 PM   #10 (permalink)
Maine Towing
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Good point, then based on what the OP said about having to prime it then air is getting into the system, not fuel leaving it.
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Lift Pump at 175,000 miles, CP3 at 299,000
ALL ON MOD - credit to GMC2500HD - best $1.29 mod you can get !!!
Air box mod
Wicked hot wife
4" Flo Pro exhaust, down pipe back, cat was stolen by some scrap iron punks That's my story and I'm sticking to it!!!

Official member of the over 300,000 mile club.

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