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04-16-2025, 07:27 PM
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#1 |
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Registered User
Join Date: Oct 2018
Location: B.C. Canada
Posts: 217
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LT4 8L90 issue
My friend Kelly and I both have LT4 8l90 crate packages. His is in a 72 Blazer, my in a 66 C10. Every since he started his he has had a check engine light. Codes are to do with the transmission solenoids. 7 codes in total. The Blazer runs and drives without any issues. He has had techs look at it and delete the codes but they always return. I bought HPtuners for my setup to change the trans shift points. Worked very well. He has talked to GM phone tech and they think it is software.
Kelly called me and I looked at the diagnostics and tried to clear with no success. I downloaded his tune and saved then uploaded my original TCU program to his. No change. He drove for a couple days as these codes are permanent and take a few cycles to clear. I just uploaded my ecu and tcu program to his successfully then immediately checked the diagnostics. The codes remain. Our next plan will to be replace his TCU, but if anyone has any ideas let me know. Last edited by vet57air; 04-16-2025 at 10:43 PM. |
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04-17-2025, 10:42 PM
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#2 |
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Registered User
Join Date: Oct 2018
Location: B.C. Canada
Posts: 217
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Re: LT4 8L90 issue
Looks like this was the wrong place to ask this. It is fixed.
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04-18-2025, 05:44 PM
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#3 | |
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Registered User
Join Date: Apr 2001
Location: DALLAS,TX
Posts: 22,571
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Re: LT4 8L90 issue
Quote:
__________________
67SWB-B.B.RetroRod 64SWB-Recycle 89CCDually-Driver/Tow Truck 99CCSWB Driver All Fleetsides @rattlecankustoms in IG Building a small, high rpm engine with the perfect bore, stroke and rod ratio is very impressive. It's like a highly skilled Morrocan sword fighter with a Damascus Steel Scimitar..... Cubic inches is like Indiana Jones with a cheap pistol. |
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04-18-2025, 11:43 PM
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#4 | |
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Registered User
Join Date: Oct 2018
Location: B.C. Canada
Posts: 217
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Re: LT4 8L90 issue
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06-01-2025, 01:25 PM
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#5 |
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Junior Member
 Join Date: May 2022
Location: Concord CA
Posts: 35
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Re: LT4 8L90 issue
Did you have HP tuners unlock the TCM?
I sent my ECU and TCM off to Speartech when I had the harness made. They told me that If I did not unlock the TCM that it would throw codes so I sent that as well, and they had HPT unlock it. I'm using a factory ecm and tcu with a pulled LT4/10L90 combo from a wrecked 2018 ZL1 |
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06-01-2025, 03:48 PM
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#6 | |
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Registered User
Join Date: Oct 2018
Location: B.C. Canada
Posts: 217
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Re: LT4 8L90 issue
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06-01-2025, 05:09 PM
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#7 |
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Junior Member
Join Date: May 2022
Location: Concord CA
Posts: 35
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Re: LT4 8L90 issue
Ok. Makes sense. He never got it sorted?
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06-01-2025, 11:58 PM
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#8 | |
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Registered User
Join Date: Oct 2018
Location: B.C. Canada
Posts: 217
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Re: LT4 8L90 issue
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