I swapped a 5.3 with s turbo into my 67 Chevelle. Reworked the stock harnessand removed the unnecessary circuits like evap, AC, transmission controls (have a th400 in it) etc... I followed the steps from LT1swap.com which was very helpful.

I have everything wired correctly except the ECT sensor.. using the schematic from LT1swap.com, the yellow wire from the ECTS goes to pin 74 on the blue (c1) connector. It shows the gray wire from the ECTS going to either pin 41 or 63 depending on where the car was manufactured. Both 41 and 63 are “pcm ground”.

I took my pcm out and checked the blue connector. 41 is empty. 63 appears to have a tan wire. When I check the pinout list on LT1swap it shows 63 on the blue connector as a o2 sensor ground....

this is where I am confused.. can I just run the ects ground to the tan wire in #63?? Or can I just ground the sensor to the engine?


i have a forged 5.3, zr1 spec cam, sheetmetal intake, SD80# injectors and a 80mm eBay turbo. i have one front o2 sensor on my downpipe. I also have an AEM AF gauge..

The harness and engine were originally dbw. I converted it to dbc and added the necessary circuits to my harness (IATsensor, tps, iac).

the pcm was flashed to clear VATS and do a basic tune to get it driveable.

It smells like it is running slightly rich and I’ve read that a bad ects (or in my case not grounded properly) can cause it to run super rich.

Anyway, I hope this was enough info. My main concern is getting the ects wired properly so I can troubleshoot from there.