Can a bad or fowled plug cause a studder or hesitation under boost or at idel?

 

of course

 

could also be a vacume leak

 

could be a bunch of things. plugs are easy to check though. wait for it to start stumblin at an idle and disconnect the plug wires one at a time. if it aint hittin on all four, the removal of one of the plug wires will not cause a change in idle. or just yank em out and look at the electrodes, but that only checks the plug. not the wire also.

 

.. and what code are you getting?

 

does OBDII detect misfires?

 

Yes it does. I know in GM cars, if a severe misfire is detected, the SES light will blink before staying on permanently. I'm not sure if other car manufactures do the same thing but its something to keep in mind.

 

what sensor is used to determine a misfire though? especially on a distributorless application...

will it verify which cylinder the misfire is coming from? it's easy to see a misfire in datamaster just because you can see the timing fall way the hell off and other sensors go to hell...but i'd kinda like to know what the car's PCM defines as a misfire

 

I'm not exactly sure what the sensors are called but yes it is possible to determine which cylinder(s) the misfire is coming from. You will need access to any run of the mill scanner so you can be sure you're pulling a misfire code (in GM's case, the code for a misfire is DTC P0300). Then using the scanner you can look up the misfire data, just go on a quick drive and it will tell you how severe the engine is misfiring on each cylinder. I do this after a plug and wire change with my car to monitor misfires and knock retard.

 

it didnt start till my plug wire started to go bad, then when it finally went bad and then i replace it the studder got just a tad worse. i was thinking it might have gotten saturated by fuel because that cyclinder wasnt firing.