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Duramax First Generation: 2001-2004 (LB7) Discuss the first generation (2001-2004 LB7) of the 6.6L Duramax diesel engine & associated components. Engine related discussion ONLY.

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Old 08-07-2019, 01:10 PM   #1 (permalink)
tonyjames28
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Intermitent fuel pressure spike / no coolant temp

Hello guys, this is my third duramax, so i have done alot to these truck through the years. Here is my issue. 01 sierra, 235,00 miles on it. Injectors, gaskets, studs by last owner. 20,000 miles ago. I had the nut back off the cp3shaft and destroy the pump, gears and front cover back in december. I pulled the engine to clean the sumps and get all 61 pieces of gear teeth out of the pans. So it has a new cp3 and fpr. all back together runs great except for when it has its problem. Intermittent high fuel rail pressure that raises the idle and you hear the injectors knocking. sometimes to 1200 rpm, but usually to around 850rpm. at the same exact time as this happens I also loose the coolant temp in the cluster, and it will also down shift into 2nd gear hard. All three happen together, never separate from each other. I have replaced the coolant sensor and plug. I throw codes p0090, p0118, p1345 and u1800. I believe it to be a harness problem but maybe more. I have taken the time atleast a dozen times going through the harness looking for rubs and just moving it around to get it to stop. Only happens about 20% of the time driving. Maybe thinking bad computer or ficm at this point. checked pins in connectors and plugs. does anybody have any thoughts. some bumps cause it to happen for a few seconds, other times for 5 minutes.

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Old 08-20-2019, 12:56 PM   #2 (permalink)
tonyjames28
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Well I was hoping for some help for all of those more experienced than myself, but I think all of the experience has moved on to newer trucks. I have gone through the harness more times, and after talking to several of folks. Since the ecm controls fuel pressure and uses the coolant temp as an input that most likely I need to find another ecm and swap it in to see if that fixes the problem. Anybody haave a good 01 lb7 ecm for sale cheap? thanks

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Old 08-21-2019, 09:38 AM   #3 (permalink)
Rvn4me
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U1800 Modules, Description:Lost Communications With Fuel Injector Control Module (FICM) Maybe a harness issue? You need to also look at your two large bale connectors LS drivers side.
https://www.dieselplace.com/forum/63...es-solved.html

P0118 Voltage high says either the sensor is shorted, or the two wires are shorted.
Adjacent to the thermostats.
Engine coolant temperature circuit voltage too high.

P1345 Modules: Description: Crankshaft Position (CKP)-Camshaft Position (CMP) Correlation
https://www.justanswer.com/chevy/48q...2or3dayok.html

Last edited by Rvn4me; 08-21-2019 at 09:56 AM.
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Old 08-28-2019, 11:50 AM   #4 (permalink)
tonyjames28
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Fixed it. After having gone through the engine harness on top of the engine a half a dozen times wire by wire and checking all of the pins, I was to the point of buying a used computer to see if that worked. Instead since this problem always all three problems at once, I thought maybe it was the computer changing fuel pressure due to temp reading. Everyone else says that there is no higher idle when cold, but one guy said there might be. So I took the harness all apart, all the way under the fuse box to the ecm connectors. Traced the wires for the coolant sensor to the ecm and snipped them there. I then ran two new wires from the ecm to the coolant sensor. It has been four days without any problems at all. I believe that it is fixed. Maybe I had a break in the wires somewhere that was intermittently losing signal. Just not sure. but hopeful I fixed it, will keep you all posted.
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Old 09-04-2019, 09:14 AM   #5 (permalink)
tonyjames28
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It has been 11 days since the repair and I have been driving it everyday everywhere. the wire replacement worked.
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Old 09-04-2019, 09:16 AM   #6 (permalink)
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Quote:
Originally Posted by tonyjames28 View Post
It has been 11 days since the repair and I have been driving it everyday everywhere. the wire replacement worked.
Glad you solved the issue.
Thanks for giving us an update!

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Old 09-04-2019, 10:46 AM   #7 (permalink)
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Thanks again for the update as well!
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