misfire on one cylinder. 1997 Legacy RS TT

Hello folks, I have been trying to diagnose and fix a rough running engine, and hope someone can please help me solve. I believe I have pinned it down to problems in the left/front cylinder.

 

Symptoms are: Rough running engine, but no change when connection is pulled from coil on plug for Cylinder #3.

 

Action taken so far: Switched coil on plug to another cylinder: fault did not follow. Switched Fuel Injectors: fault did not follow

Probed for power supply/ground at the coil connection: Two wires 12V W/ignition in run position, one wire grounded. Removed coil from cylinder, attached the connector and cranked the engine with fuel pump unplugged,

Results: visible spark on the body of the coil, lots of arcking and crackling ??

Compression test show 150 PSI dry.

Note: If I pull any of the other connectors from the other coil on plug the engine labours worst. Everything seem to be pointing me to problem from the connector back.. Can someone please say any logical suggestion as to where to check next., any would be greatly appreciated..

It's a coil over plug design correct? What about the coil driver? Is there a external ignition control module or is that inside the ECU? It would seem if your getting a signal to each coil pack then I would think sparks not the issue. Do you have a noid light? If you do then check the injector pulses at the plug because maybe the injector driver inside the ECU is fried. Just some quick thoughts, hope that helps. GL.

spooln30: GL. Thanks for the reply and the points. I ended up changing all four coil pack and spark plugs. After searching for a like problem, a youtube flick suggested to look for carbon tracking on the coil plug and spark plugs. Sure enough I had a very visible track on both. Changed out the plugs and coil and problem fixed. All of the retainer clips on the old coil on plug was broken off, not sure if a loose connection may have contributed to the arcing. Took the injectors for testing, checked ok for mechanical function, plan to replace them soon. every thing is now snugged and tight.. Thanks again for the help..

Cool and no problem man. I figured that since you swapped coil packs around and there was no change then spark wasn't the issue but I guess it was.

Go figure, electronics is a fickle business in these cars.. The problem seemed at the time to be pointing to the ECU, especially after swapping. The youtube post showed testing of the coil pack removed from the cylinder connected to the lead and tested with an ordinary test light. I did not have to test because a lot of spark was arching all over the coil. I believe I will also change out the connector with a new one, it may have simply been a loose connect because of the broken retainer on the coil. Many post a fix with zip ties.