When the front sensor went on my car, it threw codes for both sensors. Replacing just the front sensor took care of the codes. Once the code was set, and the car ran better by using the default settings than it did when trying to follow what the sensor was telling it.

After driving for a while, does the car seem hotter than it should be? Not by the temperature reading, but rather by how hot the cat seems to be getting. If I had to guess, I'd say that you have a bad O2 sensor that has also caused problems with the cat.

The hand held that we were using during the test displays the voltage in a continuos line graph. From that graph it shows the O2'* strating out and runs along the low side of the range and the jumps up to about 3/4 range (hope that makes since). The test was at idle with the computer in closed loop. Should I have done the test on the rode at highway speed?

I was thinking along the same lines. The O2 makes the engine run rich causing the Cat to clog, or the O2 making the engine run lean and burning up the Cat. Is that what your thinking? Another bit of info that I forgot about was dad ran 87 octane gas in this car and I told him time and again that its not a good idea to run low octane gas in a */c engine. I know the computer will adjust to 87 but could this contribute to a problem like this.

So you replaced the fornt O2 and the Cat and it fixed it?

I doubt the regular gas in and of itself caused the problem, unless he used leaded gas sometime. Replacing the front oxygen sensor took care of my code - AC Delco only, although some say Denso is good too - no Bosch or Borg/Warner which is what caused my problems to begin with. I'm researching cats now, as I have some issues when the car warms up in hot weather.

Well it'* been awhile but here'* what I found about the Bonny. Myself and my older bother, who is a mechanic, hooked up a scanner turned on the data stream fuction and went for a drive. On the drive the car was indicating that it was running lean. He said that if the cumputer is showing a lean condistion that it will dump more fuel into the engine giving me the cat smell. On the way back home he said he wanted to look at something when we got back. So I pulled up to the shop and popped the hood. He look at the engine and then told me to put it in drive hold the brake and give it a little gas. So I did and he said to shut it off I know what'* wrong. He said your motor mount is broken and pointed to the rubber hydraulic mount on the drivers side.

So I got the mount from the auto parts store bought the $81.00 mount put it on cleared the codes and took it for a drive. This time is switching lean rich like it'* suppose to and 200 miles later no codes and it'* running like a top.

Who would have guessed.

Why/How does a bad motor mount, allowing the motor to move.. cause a lean condition? :?:

We suspect that the engine when under load would move due to the broken mount and pulling on the wiring harness causing a short or loose connection.

Why not just unplug each O2 sensor to throw the ECM into open loop? It should do that, right?....and cause the car to run off specific parameters...JUST to see if it gets better? Naturally the light will come on..after a few, but at least the car will run consistently in "get your butt to the stealer" mode. Just a suggestion. Also, I'd check and make sure your intake hose AND intake system AFTER the MAF is leak free. I just had a hole in my Volvo V70R wagon intake tubing and it'* a slug....no SES light on either. THe MAF was measuring the incoming air, but it was puking it out AFTER the MAF/turbo. Kinda like when these rice-boiz are rapidly bolting on a Pep Boys blow-off-valve in place of their By-pass valve(by-pass valves keep the previuosly metered air into the intake but back to the front of the line, AFTER the MAF-so it doesn't measure twice).....and wondering why they get a cloud of black smoke at the tailpipe. The car is designed for and reading the air....but the recently metered air is bursting out the BOV....but the fuel is getting to the cylinders minus the metered air. Your'* could be the same...why?? Because the airleak has been actually causing the motor to run RICH (the ECM thinks it'* sending the right amount of fuel), in turn fattening the O2 sensors (to carbon buildup), but the MAF sees the proper amount of air, to the leak, to the O2, to the clogged cat (potentially). Over and over and over. I'd have to go with the MAF having priority over the O2s (which it'll be too late by the time the ECM sees a problem). The O2s are only "reading" low cause they could have carbon covering it too much...get it? Maybe...my 2 bits.

That a good suggestion but we replaced the motor mount and I've put about 250 miles on since and no SES light and it runs like a top. I think the problem may be fixed.

That is a really strange solution considering the locations of everything. It would seem that everything would move right along with the engine.

If you have the chance, could you check around and see if you can locate anything obvious? This could help our members if someone runs into a similar problem, and may also help you, as the problem could come back as the wires/connections break or corrode.