Random Misfire??

[ro25]

I have a 97 Bonneville and recently it started running roughly and with alot of hesitation. the engine light will come on and off and will flash while driving.. sometimes it feels like the car is running fine and other times it hesitates again. The computer is giving me 2 error codes #1 Random Misfire and #2 o2 sensor.. Now my question is can the o2 sensor cause a misfire??? I replaced the 2/5 coil not too long ago as it went and a week after that the module went and was replaced. i hope this is not the case again as those things were expensive.

Anyone have any ideas as to what i should do first????

Thanks
RO

[dstrass]

When did the car have new plugs installed ?

[DOpey85]

I would say just replace the rest of the coils... Thats what I had to do when I had this happen on my 93'

[Telepath]

Your problem sounds like you have an intermittently shorting spark plug wire or wires. Your description of your Check Engine Light and codes backs this up.

Remove and closely inspect each wire (one at a time) for cracks, arc spots or residue, etc. If you don't find anything obvious, look at the wires with the engine running at night and see if you see any arcing. If you don't see any arcing, (it might be a tiny little arc, so look carefully), try spraying the wires/coils with a light mist of water. It may help locate an intermittent problem. If there is any arcing going on, the water will make it arc to ground and you'll have a good idea where to look or what to replace.

Check your Throttle Position Sensor, make sure it's tight and the connector is clean and seated properly.

If your HO2S (heated oxygen sensor) #2 were bad, or worse, contaminated, it would cause major driveability problems all the time, so it's likely not that.

You may also want to consider changing your fuel filter, if it's been a while since it's been changed. If its restricted, it can cause hesitation/misfires because not enough fuel is getting to the engine. It's also a cheap ($12 or less at Wal-Mart) and easy part to change out as good routine maintenance anyway.

To answer your other question about HO2S #2 being able to cause a misfire, I think not. The HO2S provides a signal to the PCM (powertrain control module) that is one of several that the PCM uses to control fuel mixture. The HO2S has nothing to do directly with anything that could cause an intermittent misfire, such as bad wires, intermittent throttle position sensor, fuel delivery problems, clogged injector, etc....

Hope it helps.

[G-bonnedude]

Ro25 - I have a '97 Bonne myself with LITERALLY the very same problem, and so far this is what I've come up with. I have a extremely good friend who's a BMW specialist and has done diag. multiple times. I've had the throttle positioning sensor replaced, I changed 2/5 coil after multiple misfire codes (Ihad up to 5000 misfires in less than a minute then it ran perfectly for the next five min.????????) , as well as done a full tune-up. My O2 was checked by Mr.BMW who said it was fine. I don't think its the O2. After lots of research I know that I might need to replace the ECM, and as soon as I get some hands on some tools I'm gonna clean/check the EGR valve, which can get bad carbon deposits. I've been in college for the past several months and haven't been able to address the problem even though I've had 4 more error codes pop up in the past three months. I'm going up this weekend to my home-city and I'm gonna see Mr.BMW and have him pull the codes. I will get back to you mid-week next week with what I find out, 'cause I'm Determined to figure this problem out and fix it. IF ANYONE OUT THERE IS EXPERIENCING THIS PROBLEM OR HAS SOLUTIONS, PLEASE CONTACT ME, IT WOULD BE FOREVER APPRECIATED. Thanks.

[Aurora01]

I would check the crank or cam sensor or just replace easy job and not very expensive.