carriljc

QUESTION: Does the LT1 require both O2 sensors to read "good" in order to into "closed loop"?
INFO: Reading a friend's LT1 using my Autoprom.
The LT1 has 2 oxygen sensors, one of them was never going above ~450v, and the car never went into closed loop. We swapped leads, and then the opposite side sensor would never change, we checked continuity to the ECM and it appears the lead is good. At this point it would seem that the lead is fine, the sensors are fine, and that ends up making us think that perhaps the ECM is shot. I then burned him a chip with VATS turned off (just to eliminate the pro-made chip as a problem).
Well, the problem is still there, one O2 sensor doesn't react, the sensors seem fine, the leads seem fine....do y'all suppose that the actual ECM could be shot?
Hence the question:
Does the LT1 need both O2 sensor sides to be "good" prior to going into closed loop?
The one side that appears bad just hangs out at ~450v. When we swap the O2 sensor leads the opposite one looks bad. Continuity is sat from the sensor connection to the ECM. Even opened up the ECM to check that the connection at the terminals to the circuit board had continuity....that's sat. Looking more and more like the ECM, eh?

I'm usually playing with my 730 ECM and it only has one O2 sensor; it goes into closed loop as soon as that one looks good....

I gather that the LT1 needs both O2 sensors to look SAT for it to go into closed loop? Anyone know if this is true?

VenkmanP

Any dual exhaust car would need both O2s working to go in closed loop, by definition.

VenkmanP

If I understand you correctly, the problem follows the O2. How does that look like the ECM? If it follows the O2, it's the O2.

carriljc

I was really hoping that we had an OPEN in that lead, but it's good. I'm really starting to suspect the ECM. Any other ideas?

Glad to hear that it needs them both to go into closed loop. It kinda makes sense that it would need them both to be considered "good" before going into closed loop.

pcolt94

The problem is following the O2 sensor hence the ECM appears to be reading OK. Sounds like you need to try a sensor.

To go into closed loop you need;
1) 2 good operating O2 sensors producing voltages as "Vis" indicated.
2) ECT sensor above 104 deg F
3) Specific amount of time determined by ECM depending on other variables.

Otherwise open loop uses coolent temp (ECT) and MAP for A/F ratio.

carriljc

not the sensor.

With all that babbling above I probably wasn't very clear. My buddy ordered a remanufactured brain already so we'll see soon. Other than that one O2 sensor lead, the engine seems to run quite well...just really quite rich at idle since it's never going into closed loop.

pcolt94

Well while your waiting for your parts you should check the ECT temp sensor on the front of the water pump just to make sure it's not open. It should measure about 3500 ohms at 70 deg F, and goes lower as temp increases. It's a real bear to make the measurement. I used some female pins from a connector and put it over the ECT pins to bring them out in the open where I could get them easier. Other wise you can do it but its tough. Keep us posted.

carriljc

We watched it warm up after we hooked his electric fan to the computer. Warms right up and kicks the fan on at 95 degrees centigrade (~202 Degrees F).

Won't be able to check stuff for the next few days though.