[dakeller025]

hello, i have a 2008 ford focus se with 2.0. i have been having some idleing issues.i posted the other day about them and someone suggested a bad coil. i am new to these coil issues and have never tested one and was wondering if someone would steer me in the right direction of how to properly test them and what ohms they should be at....i have a decent multimeter.thanks in advance for any help.

 

[Humphrey]

You use a ohms meter to test them. Most volt meters has a ohms setting. You test them cold and hot meaning you run the engine for a while so the coil heats up.

 

[harrison.mike.j]

You can check the resistance of the coil with the ohm meter. May indicate a bad coil but it may behave differently when hot and operating. Compare resistances of each coil to one another when cold and when warm. if one is way out from the others it may have an open or shorted winding.

If you have a misfire, you can swap the coil with one from another cylinder and see if the misfire follows the coil or not.

Also there is a pretty skookum tool here that shows you if the coil is firing through induction: http://youtu.be/y7YMMlR8wc4

http://youtu.be/jbJkoX_I_WM

Most importantly, do not remove the coil and allow it to fire without proper grounding. You risk injuring yourself, fire, or damaging sensitive electronics.

 

[dakeller025]

thanks. i tested all 4 and they all read 1.0.what else could make rpm's jump around at idle?i cant really tell if it is missing while driving it.

 

[Marde]

Have you replaced the spark plugs yet? What type of spark plug are you using? What are the gaps set to?

 

[dakeller025]

yes replaced them last week. autolites the ones ford recommends.they are gapped at 50.

 

[Marde]

Do you have a scan tool or have you had the car scanned? Any DTC's : any misfire codes?

 

[Marde]

Some misfires are not really misfires; can be a fuel pressure problem, and seem like a spark problem. Ever replaced your fuel filter?

 

[Marde]

Checking the resistance of the primary-side of a COP with a meter will not tell you much. COP can still be bad, despite your meter test.

 

[dakeller025]

i have had it scanned...no codes.what is proper way of checking the coils as i dont believe this to be a fuel issue.

 

[Marde]

i have had it scanned...no codes.what is proper way of checking the coils as i dont believe this to be a fuel issue.

I have never properly/formally tested a COP. Checking for spark is one thing, checking for exact & proper operation is another. Special tool of some sort "out there" somewhere. Hopefully someone with hands-on experience of properly testing COP's comes along here to help. Check those video links above, I did not watch them yet, out of time, maybe I will watch them later.

 

[Marde]

Glad I came back here and watched those videos. Learned-Me something new. "Waycon COP tester", how cool is that!? Another quick search found this->
http://www.picoauto.com/coil-on-plug.html
...but you need a graphing meter or an oscilloscope I guess.

Plus this->
http://easyautodiagnostics.com/misc-index/cop-ignition-coil-tests-1
=five pages of COP testing glory. Scanned it very quick, looks like some good info.