My 96 420a has been having problems, it started out around 5k rpm it would stutter for a second(jump to 5.5k then down to 4.5k) now it is also doing it around 3k rpm. I do have a CEL but the only code i get is rear o2 sensor no activity. From what i have read the rear o2 sensor is only to let you know if there is a problem with the cat, so could this somehow be causing my problem? I have replaced: Coil(MSD), Plugs(NGK Platinum), Plug Wires(MSD), Front O2 sensor(I was getting that code also).

The thing that makes me think it is the rear o2 is the CEL blinks on and off as it is stuttering, if it was a spark or fuel problem i wouldn't think it would do that. Any Ideas?
Thanks

Originally posted by jmcentire
My 96 420a has been having problems, it started out around 5k rpm it would stutter for a second(jump to 5.5k then down to 4.5k) now it is also doing it around 3k rpm. I do have a CEL but the only code i get is rear o2 sensor no activity. From what i have read the rear o2 sensor is only to let you know if there is a problem with the cat, so could this somehow be causing my problem? I have replaced: Coil(MSD), Plugs(NGK Platinum), Plug Wires(MSD), Front O2 sensor(I was getting that code also). The thing that makes me think it is the rear o2 is the CEL blinks on and off as it is stuttering, if it was a spark or fuel problem i wouldn't think it would do that. Any Ideas? Thanks

A blinking CEL indicates a misfire condition on 30% or more firing opportunities. It's its misfiring, it'll blink.

Last time I had a midfire like you describe, it was my cam angle sensor harness tweaking the plug on the sensor when the engine would torque backwards under load.

Thanks for the reply, I bought a new fuel filter today(original probably never changed) and just installed it. Took it for a drive and problem was gone, however it has disappeared temporarily before, so we will see in the next few days.

Was the cel blinking because of a misfire or blinking because it was stalling and loosing power.

But Id replace the rear o2 and possibly look into a bad/clogged catalytic convertor.

Seemed to be blinking because it was stalling, I have now driven it the past couple days and have had no problems, so I think the fuel filter fixed it! Thanks for the replies.