Hi,
I have a 2002 X Type sport 2.5. I have been chasing a P0305 code (misfire cyl #5 ) for a while now. Here is where I am at: Ignition coil, spark plug and fuel injector have been replaced with new. I can use a scan tool to delete the code and all seems well until I drive about 75 miles. I drive the car about 20 miles a day. The code will re appear about 30 seconds after a cold start. I can clear the code and repeat this process.
I am due for NYS inspection in August and cannot have a check engine light. . I am interested in hearing any ideas or theories as to why I can drive for a while and then get a code. Thanks

 

Ken, I would be looking at the wiring for the coil. Odds are, the ground wire between the #5 and #3 coils has an issue and will most likely need repaired. You have done the obvious. Now we are getting into the more obscure problems.

 

Hi,
By chance do you know the wire colors for power and ground for the coils and fuel injector? I will be trying this solution this weekend.

Ken

 

Ken, I iwll do one better, PM me your e-mail address and I will send you the whole electrical diagram for your x-types. That way you have all the info that you need.

 

Hi,
Thanks for the diagram.
Coil ground appears to be the black wire. I will add an additional ground. Does anyone know why the coil has 4 wires? I am waiting for a new injector connection with a pigtail. I am desperate to pass inspection without a check engine light. I am thinking of adding a switch to turn off cyl 5 injector until I pass inspection. This is probably a crazy idea.

 

Ken, the coil has a primary coil that is hard wired to 12 VDC that builds up a field in the coil. The other 2 wires are the signal that redirect the output and sends it to the spark plug. The coil attempts to maintain the current flowing through the coil by collapsing the field. Because you have a high resistance (ie, the gap of the spark plug, the field collapses really fast and generates a high voltage to bridge that gap. That is how the spark is generated.

 

Hi,
Thanks. That makes sense now. I am trying to understand how the ECU can detect a misfire and identify the exact cylinder.

 

Ken, it is watching the up stream O2 sensor. It is watching the voltage. The computer knows that so many milliseconds after a cylinder fires the exhaust gases will pass the O2 sensor. You match up when little spikes happen at the O2 sensor, you can figure out which cylinder is not firing correctly. This is why sometimes you may get multiple cylinders misfiring, but really only 1 is.

 

It can watch the crank and see when it doesn't move as it should. That's why you have to do coast downs to set the appropriate monitor(s).

 

Success! I replaced #5 spark plug, cleaned all connectors and replaced the connector on Cyl 5. Check engine lite is gone. It took 70 miles of driving for the computer to complete the inspection ready tests. I did 3 coast down fron 70mph to 10 mph plus 5 miles of 35mph driving. State inspection good for 1 more year. .!

Thanks everyone.

 

Excellent!