First off, happy new year to all.

I'm in need of some help.

Sorry for the long post but I wanted to give some back round info. I've got a 97 Trans Am A4 converted to M6 with head work and a CC305 cam, total of 90K miles on the clock. Car has normal bolt on mods, CAI, LT headers, catback, ect. Car always drove great and ran very well after the H/C work, about 35K miles on the H/C. Plugs are new and the wires have about 10K on them, opti was changed during the H/C swap.

A few years back my life had gotten really busy and I drove the car very little, about 1000 miles in 2 years. Once I stopped driving the car it developed a lot of issues. The main issue was stumbling and stalling when driving. A few month back I finally got some extra time to find the issue. It turned out the one of the bundles of wires that runs down the passengers side fire wall had a broken loom allowing it to rest against the headers, burning many wires. This caused some blown fuses. Pulled the loom up from the bottom of the engine and found it had burned the rear O2 sensor wire (not being used due to the off road Y pipe) and the crank position senor wire completely in two. Fixed the wires, sealed them with heat shrink and rewrapped them in heat tape and remounted the wire bundle safely away from the headers.

The car ran much better but still had a slight stumble from time to time wile driving. My O2 sensors were Bosch and I had extended the O2 sensor wires by splicing in short lengths of wire for the long tube headers. I purchased the proper O2 extensions and new AC Delco O2 sensors, ditched the old spliced Bosch units. With the new sensors the scanner readings looked good and the car ran perfect, and I was very happy.

About 2 months and 100 miles later it started to misfire badly. Drove the car home and checked it on my Snap-On scanner. The bank 2 O2 sensor seemed dead(numbers moving very little), while the bank 1 sensor was functioning fine. I swapped the sensors from bank to bank to see if the problem followed the sensor. After about 15 minutes of idling the dead sensor began to show readings on the scanner again but didn't seem as active as the "good" sensor.

While I had the sensors out I took a few pictures of them. The top sensor is the bank 1 sensor (working fine), the bottom sensor is the bank 2 sensor. I don't know how dirty the sensors should normally look, these only have a few hundred miles on them.

http://memimage.cardomain.com/ride_i...jpg?544908-001

Any suggestions or opinions?

 

Sounds like there may be a problem with the heater circuit in the "slow" sensor. With long tubes and the sensor being further from the engine, the heater has to work harder to keep it hot enough to work correctly.

Looks like it may be running a bit rich, but that could be the result of cold starts, the result of not driving the car much, and the extended time required for the engine to reach closed loop. Do you still have the AIR system working?

 

Thanks for the reply Fred.

I agree it definitely seems to be running rich, and the AIR has been removed from the engine. Is the O2 heater circuit always being used or does it stop once the car goes into closed loop? Also my Snap-On scanner said my A/F ratio was 14.7, but I'm not sure how accurate it is.

I did go for a 30 minute drive with the O2s swapped from bank to bank. After driving a short distance the same problem followed the sensor to bank 1, originally it was bank 2 with the problem. Now the reading on bank 1 is 9MV at idle and 10-50 MV while driving. Bank 2 is 65-750 MV while idling and driving, which was the way bank 1 was before I swapped the sensors bank to bank. The sensor readings in bank two bounce up and down like they normally should, bank 1 readings move very little.

The engine does seem to be very rich, while driving at speeds 45-65 MPH it runs OK, apply a little throttle and the car begins to stumble and misfire. If I down shift and run the RPMs higher or go full throttle it seems to come out of it. If I let the car idle for a few minutes it will stumble and try to stall from a take off. The injector pulse readings also were different from bank 1 to bank 2.

Bank 1 injector pulse width was 5.6 at idle and 9-7 while driving.
Bank 2 injector pulse width was 2.5 at idle and 4.5-5.5 while driving.

Is the higher pulse width indicating more fuel is being added?

So is the problem a faulty O2 sensor or another issue with the engine? As I stated in my first post the car ran great after the H/C swap for about 35,000 miles. I think I may try to find one of the old bosch O2 sensors and replace it with the new AC Delco 02 sensor that seems "slow" to see what happens.

 

UPDATE:

I installed an old bosch O2 sensor in place of the "slow" new AC Delco O2 sensor and took the car for another 30 minute drive. At first it still seemed to be running rich. I ran the car pretty hard for a few minutes and it seemed to run much better. Drove for about 10 miles and the O2 sensors in both banks seemed to be working well according to the scanner readings, the injector pulse widths were dead even as well as the long and short term fuel trims per bank. With the slow AC Delco sensor the fuel trims were split badly.

So it appears that one of the new AC Delco O2 sensors is bad. I doubt that there is any way I can return it, its only a few months old and bought from gmpartsdirect.com

 

I scanner tells you what A/F ratio the PCM is using for its calculations. It does not show you what A/F ratio it is actually achieving.

The 50mV reading from the O2 sensor is causing the PCM to pour fuel into the left bank. You will find elevated BLM's (long term fuel corrections) on that side, and it uses the BLM's to calculate the pulse width. Its actually pouring in twice as much fuel on the left side. Since the faulty O2 sensor is causing a "false lean" condition, you may be pouring in enough fuel to start washing the lubrication off the cylinder walls, diluting the oil, and risking severe damage to the rings and bearings.

Everything points to a faulty sensor. It isn't "slow".... its dead..... as you eventually found out.

 

Is there anything that could have casued the new O2 to die so quickly? Or is it possible that the sensor was just a dud? I'll change the engine oil before any more driving of the car incase gas made its way into the crank case. I probally drove the car a total of 20 miles with the dead O2, hopefully there was not any damage. Thanks for the help and helpful info Fred

 

Did you apply anti-sieze to the sensors when you installed them? That can cause problems, particularly if you slop it all over the place. The sensors I have replaced came with conductive anti-sieze already on them. You can also contaminate the sensors from the outside, with oil or solvent. Once that gets into the air passage that feeds atmospheric air to the outside surface of the sensor thimble, the sensor is screwed. Anything in the exhaust system before the sensor, with silicon can contaminate it. A leaking head gasket can contaminate it with silicon from the green coolant.

 

I did use some anti-sieze but applied a very light amount to the threads and was careful when installing them not to get anti-sieze on the sensor. There shouldn't be any else in the exhaust that could contaminate the sensor, I'm not loosing any oil or coolant. I'll probally just get another new AC Delco sensor and keep a close eye on it.