Hi... tonight I started datalogging my car using TTS DataMaster software and the proper cable (with the 10Kohm resistor) and I noticed something... no matter how long I leave it idling, the ECM will never go into Close Loop... it stays in Open Loop...

The CTS will increase to 200F after awhile, the O2 voltage will start off at 450 mV and will increase to hold at around 500-575 mV....

But no Closed Loop.....

Car idles fine, revs fine, and runs fine... no Trouble codes are set

I haven't taken it on a road test while datalogging but I would imagine that it won't matter...

Is this a bad thing? I thought that it's imperative the the ECM go in Close Loop in order for you to get the most performance?

 

Since you have headers installed it may hinder your car from going into close loop while at idle. Try driving the car and you will probably see it go into C/L. I installed a heated O2 sensor in my car and its not that hard.

 

I think I have the problem diagnosed. I was chatting to my mechanic buddy (he is a GM mechanic) and I told him what was going on... he is a whiz when it comes to OBDII and the newer GM technology, that is what he diagnoses all day but he was a little rusty on the OBDI technology. Our technology is getting old I guess...

Anyway, he asked one of the older mechanics at the dealership and he said it sounded like my O2 sensor. He asked me what the O2 voltage was reading when she was idling, I told him it would go to around 550-600 mVolts and stay there. He then said that these one wire O2 sensors should be flucuating quite a bit when they are working properly. Mine is not..

He told us an easy way to determine whether or not the O2 sensor was the problem or the ECM..

1. Get the car up to operating temperature.

2. Unplug the O2 sensor and ground the terminal which goes back to the ECM

3. If the car goes into closed loop then it's the O2 sensor, if it doesn't then the problem is either the wiring going back to the ECM or the ECM itself.

Me and my buddy did the above and sure enough my car went into CLOSE LOOP.

To further check this my buddy put a known to be working O2 sensor in my tailpipe and we ran a wire back to the O2 plug under the hood. Fired her up and although she wouldn't go into closed loop (we never expected her to anyway, not with the extended wire and where the sensor was in the exhaust stream) it was clear to see that the ECM was reading the O2 sensor properly, the O2 volts were flucuating around like it should...

I picked up a new AC/Delco O2 sensor and we are going to install it tomorrow. I will let you guys know how it turns out.

 

It was the O2 sensor... POS Bosch sensor ... installed the new AC/Delco sensor and she went into closed loop like she should have....

Buying this ALDL cable and getting the DataMaster software (wish I had a freeware version cuz I only got 10 runs left) was one of the best things I have bought for my car. I think anybody that has a ECM controlled car should get these two tools (and pick up an old laptop, you can get them on eBay for dirt cheap)...

Anyway... my car idles smooth as silk now and all my sensors are reading properly

 

God Bless AC/Delco. I've never used a Bosch part that was worth crap.