I purchased a Memoscan u381 obd code reader about a year ago. It seems to work ok reading codes but my recent plug blow out started as an idle stumble. I am sure that as the plug loosened up, the cylinder was not firing properly but this did not throw a code and the live data did not show anything that I could find. This was an inexpensive unit, but I am thinking this should have shown up. Any idea's?

 

Scanner won't help unless you have an actual misfire condition for the PCM to detect.

 

What constitutes a misfire to the pcm. If a coil or plug goes bad will it see a misfire and draw a code?

 

A misfire is counted when the PCM fails to detect crankshaft acceleration when it should have.

Codes are only posted when the percentage of misfires out of the total cylinder events exceeds a calibrated limit. If you have an OBD I calibration in your SD, you may NEVER see a misfire fault code.

 

Thanks for the education I appreciate the info. I don't rely on my code reader much, I can usually tell when something is off in performance and sound after 14 years.