Hi guys, I still haven't had a chance to check my O2 voltage at the ecu with the sensor disconnected (I'm sure it will be fine, my ECM isn't faulty). If you didn't see my other post, I'm seeing my O2 sensor voltage drop to 0.00 with the car idling even in closed loop, but it jumps up into normal range at higher RPMS. I did finally cross reference the 4 wire heated O2 new AC delco sensor I'm using in the long tube header collector of my TPI 327 conversion. IIt is wired like a 3 wire but with separate grounds for the heater and sensor element, I have the grounds tied together). It is an AFS73 sensor, which acdelco.com shows for the following applications:

1995 CADILLAC CONCOURS V8 4.6L 281cid GAS FI N Engine VIN = Y
1995 CADILLAC DEVILLE V8 4.9L 300cid GAS FI N Engine VIN = B
1995 CADILLAC ELDORADO TOURING V8 4.6L 281cid GAS FI N Engine VIN = 9
1995 CADILLAC ELDORADO V8 4.6L 281cid GAS FI N Engine VIN = Y
1995 CADILLAC SEVILLE STS V8 4.6L 281cid GAS FI N Engine VIN = 9
1995 CADILLAC SEVILLE SLS V8 4.6L 281cid GAS FI N Engine VIN = Y
1995 OLDSMOBILE AURORA V8 4.0L 244cid GAS FI N Engine VIN = C
1994 CADILLAC CONCOURS V8 4.6L 281cid GAS FI N Engine VIN = Y
1994 CADILLAC DEVILLE V8 4.9L 300cid GAS FI N Engine VIN = B
1994 CADILLAC ELDORADO TOURING V8 4.6L 281cid GAS FI N Engine VIN = 9
1994 CADILLAC ELDORADO V8 4.6L 281cid GAS FI N Engine VIN = Y
1994 CADILLAC SEVILLE STS V8 4.6L 281cid GAS FI N Engine VIN = 9
1994 CADILLAC SEVILLE SLS V8 4.6L 281cid GAS FI N Engine VIN = Y
1993 CADILLAC ALLANTE V8 4.6L 281cid GAS FI N Engine VIN = 9
1993 CADILLAC ELDORADO TOURING V8 4.6L 281cid GAS FI N Engine VIN = 9
1993 CADILLAC ELDORADO SPORT V8 4.6L 281cid GAS FI N Engine VIN = Y
1993 CADILLAC SEVILLE STS V8 4.6L 281cid GAS FI N Engine VIN = 9


I got scared when I saw that this is a Northstar cadillac sensor -- is it possible this is not an old fashioned narrow band sensor, but something more exotic, that does not operate in the same range that the '165 ECU is expecting? Is there a way to check the sensor element (cold resistance) to see if it is a narrow band O2 and not something else? If all else fails, can you recommend a part # for a Delco heated O2 sensor that you know works fine with the TPI ecu's?

 

The Delco AFS-74 is one that several have recommended using.

Here is a link to te article

https://www.thirdgen.org/techbb2/sho...hreadid=263519

You can ohm out the heater only. Trying to ohm the sensing element will more than likely damage it.

 

BTW, that is a three wire sensor. I have one that's been laying on my work bench for two months. I've been so busy that I haven't had time to install it!!!!!! I need to get that done so I can do some more data logging and tune this turkey........

 

On all heated sensors, the heater ground is separated from the sensor. On all 3 and 1 wire sensors, the sensor case acts as the sensor ground. On some 4 wire sensors the case is the sensor ground along with the extra wire. On some 4 wire sensors the case is isolated from the sensor ground. I would have taken the sensor ground wire and connected it to the ECU sensor ground (any of the sensors' grounds in the engine bay will do, like TPS, or CTS). The heater wires should both be the same color (doesn't matter which goes to +/-), and the O2 sensor wire is usually the black one. That leaves sensor ground. The ECU ground could be shifted up by a little bit, and if the O2 sensor has a better ground, it will read lower. Tie the grounds together, and no more shift. BUT, don't run the heater ground through the sensor ground wire into the ECU - separate it onto a different ground.