The misfire has been ongoing for over a year, but throws no codes and no engine light.
After cleaning the fuel injectors, checking for vacuum leaks, and resistance checking the injectors, I decided on a lark to hook up a timing light.
When hooked up to any of the spark wires, the timing light will strobe normally for several seconds, until it "misses" a beat, which I can hear as a misfire out of the exhaust. I'm guessing this means there is some sort of ignition issue here, but I can't find it.
After finding a failed coil and replacing it, nothing changed. Before that, over the last several weeks, I have also replaced the cap, rotor, plugs, and wires as well as run just about every diagnostic I could find including compression tests and just watching the streaming data on a scan tool.
The miss is very subtle, but at idle is just sounds like a very slight pop every 3-4 seconds (it's not cyclical, it's very random). At light loads up to 2000 rpm, I can feel it losing power, but after that it seems to behave pretty normally. My gas mileage is about 20% less than it was before this started, though.
I have also checked for vacuum leaks, both with propane and by simply putting a hand over the throttle plate (it dies instantly). The IAC is brand new, as I was having an idle issue a few weeks ago, so I know that's not causing anything. There is no EGR valve on the car either.
I'd love to hear your input on what might be going on here and how to test for it in some way other than throwing parts at it (as the local mechanics are wan to do).
Oh, it does this whether the engine is hot or cold, doesn't seem to matter. I checked the FIAC valve, ECT sensor, and IAT sensor just to make sure they were OK, and they all checked out within spec.
have the same problem?
Tuesday, January 11th, 2011 AT 11:19 PM