Originally Posted By: mechtech2
I have no reason to believe the ignition system is as good as you say it is.
How do you know what the spark plug is doing under load in the engine? And the other parts as well ?
What tests were done?
Sure, this could be other things, but we can't rule ignition out yet.
You raise a good point, and of course the answer is I don't know. In my own experience with misfires caused by spark issues though, at idle in park it will be intermittent at best, not continual. Especially if the spark plug is firing, which it is at least to some degree that wouldn't result in non-stop misfiring. Even an improperly operating spark plug that fires occasionally will be better than one not operating at all. Not saying that's the case here, but it's enough for me to consider exploring some other options preliminarily.
Originally Posted By: mechanicx
Originally Posted By: cchase
The car is misfiring constantly, not intermittently, as though the plug is not connected at all. I ran out of checks for her to do as I'm not going to have her pull the intake plenum off and start testing the injector with a multimeter or anything like that so the car is going under the knife on Friday.
Probably best to take it in, but I like I said there is no need to take the upper intake off to test that injector circuit with a multimeter and test light because there is a 10-wire connector for that near the coil pack. Of course if it turns out the inector is bad the intake has to come off. That could get expensive although an injector can become clogged and cleaning it at the rail can sometimes get it working again. I forgot to mention the PCM can detect a electrical malfunction in the injector circuits and set a code. I imagine it has a misfire code but if there's any other codes that would be telling.
Unfortunately I'm dealing with a female with minimal automotive experience beyond what I've taught her. She doesn't have access to a multimeter and I don't have access to any electrical schematics. Your comment on a mis-operating fuel injector causing another code to trip reinforces a suspicion I had. Unfortunately when she took it to Advance Auto and had the code read they just told her it was misfire in cylinder #5 and of course she did not consider to ask if that was the only code or not. My suspicion is that there is another code as well but it's just that - a suspicion.
What is involved in removinng the intake plenum? Again, I don't have it in front of me to look at but from my memory it's just 2 gaskets, disconnecting some vacuum lines and a few bolts and it should come off, exposing the fuel rail and injector.
If it had not been #5 which is one of the more obscured rear cylinders I was going to have her try to at least use a stethoscope on the injector to see if she could hear it operating.
The vehicle does have close to 100,000 miles on it. My only concern was that I might be involved because I recently (several thousand miles ago) replaced the plugs and wires.
I considered having her swap the spark plug and wire with one on another cylinder but that would just move the misfire potentially and since she doesn't have a code reader there would be no way of knowing whether the misfire had moved to another cylinder or not, just that it was still existant.
