K, this is a baffler...97 sls, had a rebuilt put in and kept getting a misfire code. Took it to the dealer today (ASE independent installed it) to have the fuel rail recall done and take care of the SES/misfire. Injectors checked out fine, the machine said the back bank was showing misfires, but the front bank wouldn't change much when disconnecting injectors and the back would definately cause a change in how it was running. It was idling rough but would smooth out a few hundred rpm higher, though it might still be missing some just not as detectable to my ear anyway. Coil packs checked out I think, wires had spark, new plugs, new O2 sensors didn't do it...they said they found a couple of ground straps crossed, that didn't fix it....it's gonna take some more digging ($$$). They thought maybe the PCM or something got fried, don't know till they dig more. Question...is it possible to fry something just doing a swap? Anybody run across something like this before? It might not be the PCM, but it's sure got alot of people baffled. Any help would sure be appreciated...Thanks
Oh, only that code came up, one other in the history was all the codes on car...they told me I probably shouldn't have driven it the 70 miles to the dealer, the SES light wasn't flashing, just stayed on, so left it there and am trying to get some insight from the people in the know.

Well, compression, spark, fuel.

Did they do a compression test? Scope the ignition?

You could have the injectors cleaned and tested.

Well if the back bank causes a change then the back bank is running good. Whatever gives the least amount of change when disconnected is where the problem is located. Maybe they gapped the spark plugs wrong. If you know what cylenders are misfiring then you can run the engine for a little while, turn it off then take out the spark plugs from the cylenders that are misfiring. If they smell like gas and are a little wet then its an electrical problem, if not then its most likely a fuel problem. I would still double check the gap on the plugs, just because its easy to do.

Thanks, they did a compression test and they were all almost identical, they tested the injectors when they did the fuel rail, everything fine there. I'm not sure how many O2 sensors they replaced...The old motor had coolant on at least one cylinder, would that throw all the sensors, also, what would the coolant running through the exhaust do to the cat? The thing thats throwing us it's the only code that came up, misfire...would the EGR valve do it? I'm going to bring the darn thing home and start with the simple stuff first and keep going I guess.

Oh, they had the scope hooked up to the coil packs too.

Antifreeze can and will ruin the O2 sensors.