intermittent misfire

[brake]

I’ve got an intermittent misfire that I can only seem to notice at idle.

Topic

[dreamer2355]

Have you tried to do a power balance test to see if you can isolate the cylinder?

And do you have access to a scan tool that will show cylinder misfire counts or a bi-directional scan tool that can operate the IACV and EGR?

Out of curiosity what plugs are in the vehicle?

Any signs of coolant loss as those engines are known for bad lower intake manifold gasket leaks?

Have you checked for vacuum leaks or even used a vacuum gauge and studied the readings?

Keep us posted.

[Matt]

If you haven’t replaced the wires, I would definitely inspect them at the very least. I had a misfire on my four-popper Geo Prizm. I replaced the plugs, and while doing so, I found two of the wires had rubbed together so much that they had almost melded into one wire, because there was almost no insulation left between the two. Do you have a check engine light on by chance? Those coils ‘usually’ fail two cylinders at a time, but I was taught by my very GM-ish advanced diagnostics instructor that that is definitely not always the case, so you might try getting a known good coil, possibly from a scrap yard, and swapping them out one at a time to see if the problems goes away.

[Cheviac]

I would also check the wiring leading from the computer to the coil packs. In some vehicles, these wires can become frayed over time and cause a short. Happen to me in my old Dodge Caravan. Fixed the exposed wire and all was good.

[college man]

I’m for the power balance test. if nothing found. then onto vacuum leak testing.good luck and keep us posted.

[djdevon3]

Check the spark plugs for signs of wear. If it’s a voltage leak it could happen anywhere from the plugs to the coil.

[EricTheCarGuy]

Here is a link to a video I did on finding voltage leaks that might be a good place to start.
http://www.youtube.com/watch?v=x-U9WqJfaJs

[djdevon3]

Eric I’m sure he’s already watched that one as he sourced it in his original post. 😉

[EricTheCarGuy]

Quoted From djdevon3:

Eric I’m sure he’s already watched that one as he sourced it in his original post. 😉

It all kind of runs together after a while sorry. Still it does seem like an ignition issue at least that’s where I would start my search.

[brake]

I’m fairly confident it’s an ignition problem as well, couldn’t find any vacuum leaks whatsoever.

Gonna look closer at the wires…didn’t find any voltage leaks but that doesn’t mean there aren’t any. I checked around the wires and all of the boots at night with a test light, didn’t get a light show at all. If I can’t find anything, a new set of wires is only like 35 bucks, and since I have no idea of their age it wouldn’t hurt me to replace ’em.

Haven’t done a power balance test because it’s been miserable outside. I’ll get to it soon and let you know.

[brake]

It will be kind of hard to notice it since it’s intermittent and so hard to hear from under the hood (it’s noticeable in the car moreso, you feel the shudders through the wheel and seat)

[Author]

Replies