Driving my 850 when the temp gauge gets to the middle (warm ) it will get a hard miss about every 10 seconds, like the key is turned off/on very quickly. the tach also takes a quick dip, and never has thrown a code. . The only codes I have gotten in the past is knock sensor,, and Cat efficiency. It has about 240 K on it and otherwise runs very well, Did a full tune about 15k ago with all good parts from IPD. Swapped fuel relays. cleaned MAF, checked cap/rotor,.. When it's cool out it does not do it.. it's about 80-90 outside here now. Could the Cat be the problem? Did a search and didn't find anything.
Thanks, Tim

 

Just got back from hot drive, Cat reads 462 at front, 320 at back.. Bad Cat??

 

If the tach drops to zero, I think it's the crank sensor. Magnets are affected by temperature.

The program in the ECM could have lots of features that I don't know about, but I would not think a quick misfire performed deliberately by the ECM would help the catalytic converter. It's not something that would be related by natural causes, for sure. The lack of reaction efficiency in the cat doesn't affect anything except emissions and that is detected by the rear O2 sensor.

 

That's a good call, I'll get one ordered up and replace, Thanks,

 

Replaced the cat,, and crank sensor, no problem yet, Did notice the connection blocks on crank and cam sensor very corroded, green.. cleaned both and put back on with dielectic grease.
Tim