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[Elmstoneboy]

I first had this misfire about a month ago. ECU reports random misfire & misfire on no 2 cylinder.
It first happened just on startup at sub 1000rpm and when revved higher, cleared itself. This didn't happen every time, just now and then. No lights came up on dash at this stage. After a few days it seemed to clear itself and didn't happen again for about 10 days,
missfired a bit on startup, but cleared as before with engine running smooth. About a couple of miles later I got stuck behind an eco warrior doing 25mph which, with the auto box meant most of the time the revs were below 1000rpm. The engine then started to misfire even at higher revs and the EML started to flash for a while and then stayed on and I assume went into get you home mode.
I decided to pull over and switched of the engine, then restarted and all was back to normal with engine running smooth and normal, and EML stayed off. Everything was then ok for about a week until last night and it happened again. Same situation got stuck behind a car doing 25mph and back came the misfire with EML lighting up. Pulled up switched off restarted and all ok again.
Came to work this morning without any hint of a problem. Why??
At first as other people, though it may be coil pack, but would this be cured by switching engine off and on again? Oil or water around plugs? haven't had a look yet, but again would a restart cure this? I wouldn't have thought so.
Any suggestions. It's going for it MOT next week so a good time to get the garage to do something.
Almost forgot  Engine has done just over 60,000miles

[sjr47]

Seems classic crank sensor fault not had the problem myself (yet) touch wood but plenty of posts on here giving the same symptoms try and get EML codes if any to confirm.

[tunnie]

Does not sound like crank sensor to me, no stalling, only miss-fire 

First things first, read the codes via pedal trick. Details in the maintenance section 

I'd also pop the coil packs out, check for oil/water 

[Paddy Flannery]

I agree with Tunnie that your symptoms don't suggest crank sensor.
Look in the maintenance guide for the pedal trick and post the codes up on the forum. If that leads you to pop the coil packs off, when was she last treated to new plugs ?

If no oil or water in the wells, maybe a plug has developed a crack ?

Same symptoms that I had recently and new plugs and coil pack were required after plug wells found to be full of oil and water. One of the plugs had tiny crack developing too.

Cam cover gaskets replaced to prevent further oil ingress and scuttle sealed to prevent water ingress from attacking the 2-4-6 coilpack. 

[Elmstoneboy]

Hi Paddy & Tunnie

I did give the results of the pedal trick in my first line . The codes were 0300 & 0302 and these are the only ones reported
since the problem started.  Another thing crossed my mind, is that it seems that if the engine warms up without a misfire
then it doesn't do it for the rest of the journey. The two times it did, it had only traveled a mile and wouldn't have warmed up much. Just a thought. The garage has said that it will put it on TechII when I go in for the MOT. I will also pass on any suggestions that sound reasonable from the group, so any more would be welcome either to back up the previous, or new.

Thanks for the help.

Forgot to mention, plugs were replaced about 6 months ago.

[Paddy Flannery]

Yep, I recognise the bit about starting fine and running for a mile or so before starting to cough and causing the EML to flash initially and then stay on.

For me it was a new 2-4-6 coilpack that cured it. Genuine Bosch. 

[Elmstoneboy]

Thanks Paddy that can be first on my list for the garage

[tunnie]

Have you taken coil packs out? Lot can change in 6 months 

[Elmstoneboy]

No I haven't tunnie, haven't got any cover myself and its rained for the last 6 months 

It looks like the coil pack is the main contender at the moment.

What I can't understand, is why, if the coil pack is faulty does it correct itself, just by turning the ignition off and on again 

[dbug]

Agree with above - definitely not symptomic of a failing crank sensor - as said check plug wells for water/oil, remove and check visual condition of coil packs and plugs

[Andy H]

No I haven't tunnie, haven't got any cover myself and its rained for the last 6 months 

It looks like the coil pack is the main contender at the moment.

What I can't understand, is why, if the coil pack is faulty does it correct itself, just by turning the ignition off and on again 

If the ECU detects a misfire it can shut off the fuel to the offending cylinder to prevent unburnt fuel damaging the catalytic converter. When it does this it goes into limp mode and lights the spanner light which stays on until the engine is restarted.

[Elmstoneboy]

Thanks Andy,  All is becoming clearer now 

[tunnie]

Thanks Andy,  All is becoming clearer now 

Also if water/oil is sloshing around in the plug, it can cause it to miss-fire then behave.

Coil packs do fail, it's quite possible it's burnt out. Could have been made worse if oil/water in the plugs, but as they are quite expensive, you want to be sure that's at fault 

[Webby the Bear]

Do visual checks on coilpacks where they connect to the plugs (rust and white marks where it may have been arcing) and also hooking a multimeter up to test for resistance. Specs on Autodata so if you have a DVOM I can check next week the specs (pm me if you do). or perhaps someone else on here can if it's urgent.

Plus the aforementioned oil/water in plug well checks.

 

[Webby the Bear]

Ps, I remember from my 'Mechanic School Blog' that Mark DTM said the resistance check was a poor test and that thebest test was an adjustable gap spark plug. If you read this Mark...

Do you mean hooking up the spark plug in the removed coil pack and grounding it to the head whilst cranking.... and then adjust the gap mm by mm to see if it still sparks good?