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[Webby the Bear]

Hi guys,

As above, am I ok to unplug them and plug them back in individually to find the problem cylinder? Really don't want to shock myself.

I suppose I could turn car off, unplug coilpack and start the car up. if it sounds the same and theres no change then I've found the problem cylinder?

[omega3000]

Ive done that on the V6 and never got a shock ..but you mite get one  I couldnt find the bad one  ended up the coil pack was all split 

[aaronjb]

If you're unplugging the LT side (i.e. the plug going into the coilpack, not the coilpack from the spark plug) then you'll be perfectly* safe.

The HT side, not so much..

(*as safe as you can be handling 12V DC in a big insulated plastic plug, anyway )

[Webby the Bear]

haha that's what im trying to avoid 

aaron, very good point. if I unplug them with car off. then start car up. so im nowhere near it. that would work wouldn't it?

[Kevin Wood]

Generally, if a car is advanced enough to have coil-per-plug ignition, it will report misfiring cylinders to an OBDII code reader.

The HT side of such coils can generate very high energy sparks, and the insulation in the coil can sometimes be damaged by firing it without a load, so I'd be very wary of pulling them off like plug leads.

The best way to diagnose would be by checking the fault codes.

Oh, and if you interrupt either the LT or HT side when running, bear in mind that the ECU will blacklist the cylinder and disable fuel to it, and it won't then stop misfiring until you replace the coil and re-start the engine.

[aaronjb]

haha that's what im trying to avoid 

aaron, very good point. if I unplug them with car off. then start car up. so im nowhere near it. that would work wouldn't it?

If the car has individual coils (coil on plug?) then you should be able to disconnect the plug (usually several wires) going into the coil - the 12V low tension side. In which case you can unplug it with the car running and there's no (or very little) risk of a shock, plus you don't risk damaging the coils trying to fire them into 'nothing' as Kev says.

That's exactly what I did on the M3 when checking my misfire out. I also swapped the coil between cylinders to make sure it was the coil and not the injector/plug, but I did that with the car off as it means interrupting the HT side!

What car are we talking about, out of interest?

[aaronjb]

Oh, and if you interrupt either the LT or HT side when running, bear in mind that the ECU will blacklist the cylinder and disable fuel to it, and it won't then stop misfiring until you replace the coil and re-start the engine.

Not always, in my experience.. though I imagine it depends on the ECU - the M3 would happily let me unplug cylinders and they restarted as soon as the plug was replaced; though that was under no load (at idle), I can't speak for other circumstances or cars

[Webby the Bear]

thanks guys. its the 2003 Renault scenic I serviced yesterday. she bought it to me with a check engine light. but as I don't have a code reader I though id use some rudimentary diagnosis.

[Webby the Bear]

If I unplug the connector going to the CP then even if the fuel is cut off by the ECU then that shouldn't matter should it? Bearing in mind i'm cutting off the spark anyway?

ill still probably disconnect the connector (LT side) and then start the car up just to doubly make sure I don't get fried 

[henryd]

thanks guys. its the 2003 Renault scenic I serviced yesterday. she bought it to me with a check engine light. but as I don't have a code reader I though id use some rudimentary diagnosis.

To be honest Webby,if one coil has failed the rest won't be far behind(been there with renault a few times ) why not replace all four,they aren't very expensive

[henryd]

In the picture you posted of the plugs out of it the one that is dark and clean belongs to the duff coil IMO

http://i1226.photobucket.com/albums/ee402/webbybear1/lo4_zps9f2d6e68.jpg

[Webby the Bear]

that's a really good point thanks for spotting that mate!

is that cos its cleaned with fuel but obviously not burning?

[Kevin Wood]

In the picture you posted of the plugs out of it the one that is dark and clean belongs to the duff coil IMO

http://i1226.photobucket.com/albums/ee402/webbybear1/lo4_zps9f2d6e68.jpg

Yep, that looks pretty conclusive!

[dbug]

In the picture you posted of the plugs out of it the one that is dark and clean belongs to the duff coil IMO

http://i1226.photobucket.com/albums/ee402/webbybear1/lo4_zps9f2d6e68.jpg

Elementary

[Webby the Bear]

Can I just check we're in agreement that its cylinder 2? looks like its been cleaned by fuel thus confirming fuel delivery?

just bought a CP from GSF parts. £16 inc vat