Porsche Enthusiasts Club Forum

From using the info on this link. ...

http://www.secondchancegarage.com/publi ... ooting.cfm

...it would seem my coil readings are way different.

I get 0.6 ohms on the primary circuit and 6.9k ohms on the secondary.

Should the coil on a 944S 16v ignition read the same as on the link?

Hi, according to Clarks Garage the readings you are getting are fine:

Ignition Coil Resistance Check

In addition to the test above, you may elect to perform an ignition coil resistance check as confirmation of the coil's condition.
1.Check the ignition coil primary coil resistance by connecting an ohmmeter between the positive (Black wire) and negative (Green wire) terminals on the coil. The resistance should be 0.4 to 0.6 ohms.
2.Check the ignition coil secondary coil resistance by connecting an ohmmeter between the coil output terminal and the ignition coil negative terminal. The resistance should be 5000 to 7200 ohms.

I think all the coils on the 944 models are basically the same spec, hope that helps.

Thanks. Just trying to find the cause of my idle misfire once its warmed up. I had my idle co2 sorted by I'm getting raised hydrocarbons so thinking possibly the coil is failing after it heats up and producing a weaker spark and therefore a poor fuel burn.

Had the inlet manifold off and have no vacuum leaks.

Hi, it's unusual for the coil to fail, but not impossible. However, it is driven from the ignition module on the RH side just under the expansion tank and behind the headlight. This is an electronic device and they can fail when they get warm, or it could simply be contact resistance due to corrosion and tarnish. I would suggest you have a good look at the contacts and clean them and spray WD in there too. Even if this is not the cause, it is good preventative maintenance. I have experienced several issues due to this device playing up.

Thanks again.

I've just let the car idle for 5 mins or so and checked the coil again

0.8 ohms and 7.4k ohms so the resistance is increasing as the coil warms up, is this normal?

Also looked at the ignition module, seems to be some aftermarket one, no bosch number on it at all.

Hi, the copper wire in the coil has a Positive Temperature Coefficient of resistance which is directly proportional to its temperature. so, I would expect the resistance to increase with an increase in temperature and decrease with a decrease in temperature.

If you can get your hands on a Bosch module it might be useful to do a swap and see what happens - I was helping another forum member recently and he bought a brand new non-OEM module and that was dead on arrival, so the quality of these items cannot necessarily be taken for granted. I sourced a good second-hand one and that is now in his car - and on the road too!

If you have a Porsche breaker nearby, go and have a word. It is always good to have one of these modules on the shelf - just in case.

I may just buy a new bosch coil and module anyway, not going to do it any harm and it will complete the replacing of all the ignition items which I was intending to do anyway.