Coil Packs

[Poledriver]

I think that one cylinder may be very low on power and I have a bit of a mis-fire too. In the past I would have run the engine and taken the HT leads off in turn to find one which didn't have much effect. Is it safe to do this with the inputleads to the individual local coils on each plug?

[stevieturbo]

I dont see why it would pose a problem...

Either that, or unplug an injector wire.

[The PM]

May cause the ECU to record a fault (even go into limp home mode) on turn on the dash warning light.

[Poledriver]

That's what was worrying me!

[GreenV8S]

Deliberately causing a misfire by pulling leads off may make the situation worse. Better to test the exhaust manifold temperatures close to the head. A plastic cable tie held against the exhaust for a few seconds will quickly melt if that cylinder is firing.

[rev-erend]

I bought one of those lazer temp guages - very useful tool for about £20 from ebay.

I've also pulled all my plug leads off and put a new set of plugs on the and placed them on the plenum .. then turned the lights off and cranked it over... to see how good the spark is.

With wasted spark and coil packs .. there are planty of sparks !

[Poledriver]

GreenV8S said:

Deliberately causing a misfire by pulling leads off may make the situation worse. Better to test the exhaust manifold temperatures close to the head. A plastic cable tie held against the exhaust for a few seconds will quickly melt if that cylinder is firing.

Ingenious! I like that and will give it a try when I get to work tomorrow. Thanks!

[GreenV8S]

rev-erend said:

I've also pulled all my plug leads off and put a new set of plugs on the and placed them on the plenum .. then turned the lights off and cranked it over... to see how good the spark is.

Have you tried cranking it for a few seconds longer to see what happens when the fuel/air mixture blown out of the plug holes gets as far as the plugs? Nasty stuff, petrol vapour.

[ELAN+2]

if its a coil pack problem, you will have 2 cylinders down, not 1, more likely to be a problem with the valves/plug/plug lead/injector/rings etc on the dodgy pot. Infrared temp gauge is good for looking for miss fires (cooler exhaust runner).

good luck

(dont like the idea of melting cable ties on exhaust pipes though!

[Poledriver]

ELAN+2 said:

if its a coil pack problem, you will have 2 cylinders down, not 1, more likely to be a problem with the valves/plug/plug lead/injector/rings etc on the dodgy pot. Infrared temp gauge is good for looking for miss fires (cooler exhaust runner).

good luck

(dont like the idea of melting cable ties on exhaust pipes though!

Why would it affect 2 cylinders? There's a seperate coil for each plug. Sorry, I'm still used to one coil and a distributor!

[rev-erend]

GreenV8S said:

rev-erend said:

I've also pulled all my plug leads off and put a new set of plugs on the and placed them on the plenum .. then turned the lights off and cranked it over... to see how good the spark is.

Have you tried cranking it for a few seconds longer to see what happens when the fuel/air mixture blown out of the plug holes gets as far as the plugs? Nasty stuff, petrol vapour.

The exact reason why I did not remove the plugs.. and used a spare set.. plus it takes ages to remove all 8 plugs

[Mr2Mike]

GreenV8S said:

Deliberately causing a misfire by pulling leads off may make the situation worse. Better to test the exhaust manifold temperatures close to the head. A plastic cable tie held against the exhaust for a few seconds will quickly melt if that cylinder is firing.

That's useful if a cylinder isn't firing at all, but a misfiring cylinder could still get an exhaust manifold hot enough to melt plastic.

If the misfire hasn't caused the MIL to illuminate then unplugging an individual coil pack is most unlikely to cause it. I took off the coil pack plugs and the injector plugs one at a time on my Fiat Coupe to track down a misfire with no ill effects.

[BB-Q]

When I have this problem at work (usually with Renaults. Coil On Plug and yet still wired as wasted spark- bleedin' Frogs) I just unplug each injector in turn. You only need to do this for a split second to find the cylinder. Considering you already have this misfire I'm surprised your MIL light isn't on already. What car are we talking about?

[Poledriver]

BB-Q said:

When I have this problem at work (usually with Renaults. Coil On Plug and yet still wired as wasted spark- bleedin' Frogs) I just unplug each injector in turn. You only need to do this for a split second to find the cylinder. Considering you already have this misfire I'm surprised your MIL light isn't on already. What car are we talking about?

Sorry, just dawned on me that I hadn't mentioned the car!
It's an MGZT-T 260.

[ELAN+2]

Poledriver said:

ELAN+2 said:

if its a coil pack problem, you will have 2 cylinders down, not 1, more likely to be a problem with the valves/plug/plug lead/injector/rings etc on the dodgy pot. Infrared temp gauge is good for looking for miss fires (cooler exhaust runner).

good luck

(dont like the idea of melting cable ties on exhaust pipes though!

Why would it affect 2 cylinders? There's a seperate coil for each plug. Sorry, I'm still used to one coil and a distributor!

sorry miss read and thought as the thread title was coil pack, it was a coil pack issue, if its a coil per plug, then pulling the low tension connection from each coil in turn should indicate the iffy one, or use a code reader for the DTC that should be stored. again assuming its a car engine? if its a bike then DTCs wont be an issue unless its almost new

Edited by ELAN+2 on Wednesday 7th May 00:07