Check Engine

[lobodude45]

Hey guys I have a '98 M3 and my check engine light keeps on coming on weekly for the past 3 weeks after I reset it with the Peake tool. The same 2 codes I am getting are: E5: PreCat oxygen sensor response time, Cyl. # 1-3. The other code is F2: Misfire detected, Cyl. #5. The car has 72,000 miles and still seems to run very well. All plugs and plug boots were changed last year. I always burn premium fuel. I chipped the car this spring with the Shark injector, do you think this has something to do with this? Any help would be greatly appreciated.

[Jeron]

Do you get the same two codes each time?

It isn't uncommon to have a bad O2 sensor, but you should make sure that your code means the O2 is bad. I am not sure if there is more than one type of O2 fault.

The misfire could be many things. It isn't a big deal if it happens once a year but if it is every week then you have a problem. I would start by checking for oil in the plug well. Then pull the plug and look for fouling.

You say the boots were replaced, did you replace the coils too or just the boot that runs from the coil down to the plug? Coils are a common failure too and it is recommended to replace them as a set. Make sure you put both (2 for the entire engine) ground leads back on the coils when you reinstalled them.