Good evening, all - troubleshooting the P0316 (Engine Misfire Detected on Startup) and P0306 (cylinder 6 misfire) DTCs in my son's 2002 mustang and need a sounding board to confirm my tests and resulting observations. Typical of misfires, the car is running rough and exhaust smells of gas, but will not die.
Spark:
- New plugs/wires installed 21mos/19k miles ago. Pulled plug wire #6 (and later the others) from coil pack and could see the spark arcing to the wire. Car seemed to run noticeably worse, leading me to (maybe wrongly) think it was working when connected.
- connected a spark plug tester to the end of #6 wire and saw arcing there as well.
- pulled #6 spark plug with wire connected and turned engine over - saw plug end arcing.
- swapped #4 & #6 plugs and wires and cleared DTCs. No change in rough idle and both DTCs (still indicating #6) returned after a few minutes
Fuel:
- CCRM, Fuel pump & filter replaced 12mos/15k miles ago. OBD2 reader shows consistent 38-45 psi pressure in fuel rail
- All new Motorcraft injectors installed 18mos/18k miles ago. Checking with an automotive stethoscope, I can hear the distinct ticking of each one (including #6) as it fires.
Compression:
- trouble here: try as I might, could not get the compression tester fitting to screw into spark plug hole (it's threads don't seem to be tapered).
Observation:
I think the spark and fuel tests above are enough to at least isolate the issue to the cylinder itself (valves, head gasket, piston or rings) but want other opinions. Is seeing a strong spark arcing from all six spots on the coil pack enough to rule it out? Is hearing the distinct ticking of the injector (and smelling fuel) enough to rule it out?
While I search for a tapered fitting, I am open to suggestions for further testing. A couple of (fairly) easy ones that just came to mind are using my HF laser thermometer to check the exhaust manifolds, and removing the valve cover to check #6's valve springs. Maybe I'll get lucky and find one broken.
Thanks for any guidance.
Spark:
- New plugs/wires installed 21mos/19k miles ago. Pulled plug wire #6 (and later the others) from coil pack and could see the spark arcing to the wire. Car seemed to run noticeably worse, leading me to (maybe wrongly) think it was working when connected.
- connected a spark plug tester to the end of #6 wire and saw arcing there as well.
- pulled #6 spark plug with wire connected and turned engine over - saw plug end arcing.
- swapped #4 & #6 plugs and wires and cleared DTCs. No change in rough idle and both DTCs (still indicating #6) returned after a few minutes
Fuel:
- CCRM, Fuel pump & filter replaced 12mos/15k miles ago. OBD2 reader shows consistent 38-45 psi pressure in fuel rail
- All new Motorcraft injectors installed 18mos/18k miles ago. Checking with an automotive stethoscope, I can hear the distinct ticking of each one (including #6) as it fires.
Compression:
- trouble here: try as I might, could not get the compression tester fitting to screw into spark plug hole (it's threads don't seem to be tapered).
Observation:
I think the spark and fuel tests above are enough to at least isolate the issue to the cylinder itself (valves, head gasket, piston or rings) but want other opinions. Is seeing a strong spark arcing from all six spots on the coil pack enough to rule it out? Is hearing the distinct ticking of the injector (and smelling fuel) enough to rule it out?
While I search for a tapered fitting, I am open to suggestions for further testing. A couple of (fairly) easy ones that just came to mind are using my HF laser thermometer to check the exhaust manifolds, and removing the valve cover to check #6's valve springs. Maybe I'll get lucky and find one broken.
Thanks for any guidance.