Testing coils & HT leads with multimeter?
 

I'm running Bosch MEC-723 coils & Magnecor HT leads on my MY95 & i've had this intermittent misfire problem.

It started a few months back just before a re-map :rolleyes: I changed the spark plugs & it still did it but then I re-gapped them from 0.7mm to 0.6mm & it ran like a beauty.

The problem has now come back again & I thought maybe i'm cooking the plugs (PFR6-B's) & changed them again. This time to no avail, the problem remains whilst gapped at 0.6mm. Now the car is misfiring on tickover :eek: It runs fine whilst cruising but as soon as you pull up to traffic it starts to misfire & on boost it misfires :(

I've got a multimeter but 90% of the time don't know what to use it for unless told. I was wondering how i'd use it to test my coils & leads as i'm beginning to think that one of those might be the culprit :)

Any help would be appreciated so I can take another look tomorrow :)

Oh & if anyone has any other suggestions i'd be grateful :)

Thanks

MAFFA

I take you got "normal" coils, if so remove the rubber shroud from them and check for hairline splits/cracks if you see any there's your problem.

They're MEC-723's so no they're not normal. MY95's normally have coil packs which i've discarded in favour of the upgraded Bosch ones. They are the same as the ones in the link below:

http://www.mocomracing.com/product_d...&cat=16&sub=46

MAFFA

Tick-over misfire is unusual. I s there a lot of dampness getting into the coil spark plug area? Does it get better or worse as the engine gets hot?

Is the remap a scooby ecu then. Misfire symptoms similar to bad coils can occure with badly fitted scoobyecu chps/boards. check all the soldering on the ecu. With ECU board connections tt can be fine as you start off but get worse at the heat builds up in the chip.

Only other thing is to try original coils. Those bosch coils you've got are supposed to be better but you never know.

PFR7's should be fine at 0.6mm at boost above 16 psi and should also be fine with 0.7mm at boost up to 16 psi - what boost are you running?

As for using a mulitmeter I do not know. I presume the coil must have a standard resistance but unless you are actually putting the high PD across them at their operating temp I guess it would be hard to diagnose anything - thats my guess anyway.

1) No not much dampness at all
2) I'm running an Apexi PFC & AVC-R at 1.4bar peak
3) It get's worse when the engine is hotter
4) They're PFR6's & not PFR7's

Thought it was easier to answer all the questions like that :D LOL

MAFFA

Okay so today I took my car apart again :D

1) I re-gapped all the plugs again & tested them all with the multimeter for resistance - 4.65 ohms approx on each.

2) I tested all of the coils for resistance and they came out at 7 to 8 Ohms on each.

3) I then tested each of my HT leads & they were all fine as well!! :rolleyes:

I dunno now? It's more under load that i'm getting a missfire than anything else now so i'm definately thinking coil or plug. I think I might go for a colder plug than the PFR6's as maybe the coils & leads just keep cooking them? I might change the fuel filter whilst i'm at it as well. That's done over 20k.

If no joy i'll look to the leads or coils but i'm lost atm :( You put your foot down & there's hardly any pull & it feels like it's running on 3 cylinders!

MAFFA