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Old 03-04-2013, 08:50 PM
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GM Tbi wiring harness

My plan is to use a GM tbi on my 348, I have all the stuff and factory harness. I was going to just order a ready harness for it but I seem to be spending alot of money lately so I am going to try to get the factory harness to work to save a little cost.I have done alot of web searching and found alot of info but thought I better ask if anyone has any advice or web links to look at. thanks Seth.

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Old 03-05-2013, 05:22 PM
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Get a wiring Diagram for the powetrain management (EFI Sytem) and use that as your guide.You should be able to check the schematic and the harness you have to see where you need to apply power, key on/off power and all the wires needed and color codes...etc.
Dont forget about fuel line and in tank pump.
I have used nylon fuel line in the past with good results and it is pretty inexspensive.
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Old 03-06-2013, 07:27 AM
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You have to use all the sensors unless you send out the TBI computer for a reflash. They are really sensitive to any cam changes in thier original application. Where are You putting the knock sensor? The coolant temperature sensor is critical in these also.
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Old 03-06-2013, 09:13 AM
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The '87 TBI system is somewhat popular as a retrofit because it was not as well intergrated into the trucks and more stand alone, being last year of the '73-'87 body style and first year of EFI. '88-'93 can work also but the harness is a bit more intergrated into the trucks systems. Not sure how you will tune it to run a 348 with a factory ECU. something like a Megasquirt II with a TBI would be easy to get going on a 348
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Old 03-06-2013, 12:09 PM
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The best factory harness, if you can find one, is the harness from a 1989-1990 Caprice with TBI. This is a totally stand-alone harness that routes into the engine compartment through a grommet on the passenger side of the firewall, under the HVAC box. Remove the inner fender and you can pull the entire harness out in one piece. This harness only controls the TBI and related emissions components - the only connections to the rest of the electrical system are for power and ground. The harness runs under the dash to the ECU and the ALDL connector, with a connection to the Check Engine light and power. Unfortunately these cars are relatively rare in wrecking yards and the 91-96 harness is different and more integrated.
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Old 03-07-2013, 08:32 PM
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Thanks for the replys, I dug out my harness and ECM and it is out of a 90 CK1500 pickup. I got it pretty well cleaned up now per instructions. However I am definitly going to our local auto yard and look to see if they have an 89-90 caprice, that would be great.As for tuning on the 348, I was hoping that with a stock build it would run close enough to a sbc 350 that it would work good.
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Old 03-07-2013, 08:35 PM
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Quote:
Originally Posted by 455olds View Post
You have to use all the sensors unless you send out the TBI computer for a reflash. They are really sensitive to any cam changes in thier original application. Where are You putting the knock sensor? The coolant temperature sensor is critical in these also.

I have all the stock sensors, I was going to put the temp sensor and the knock sensor in the same places as the donor motor. I belive the knock sensor is on the right side in the block drain plug and the temp sensor is in the intake. I need to look agian for sure.
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Old 03-08-2013, 08:05 AM
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I think you are right. My '88 GMC has the knock sensor on the right and coolant temp by thermostat.
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