New coils, new plugs, STILL misfiring!

[AJP]

Recently I've been getting heavy misfires under load. Engine light flashed, then stayed on. I knew the coils were old so yesterday I replaced all 4 with new R8 coils sourced from AKS. I got the car scanned and cleared the fault codes:



Took it for a good blast and it all seemed fine. Yet today, the misfire is back. Under load, coming onto boost, and it bucks and splutters with big pops out of the exhaust.

Now I'm thinking it can't be plugs, as these were new 2k ago, fitted at Statller.

One thing I have noticed recently is a slight metallic 'rattle' or 'tinkling' with a cold engine coming onto boost - obviously on very light throttle and changing up at 2200rpm or so. I'm very careful to treat it sympathetically when it's warming up. I don't hear this noise when it's up to temp.

Reading up on this led me to the theory of a loose wastegate. So, is there a chance I have a dodgy N75, considering it shudders and misfires just as boost is building? The misfire specifically on cyl 2 tells me it's not, but I'm not ruling anything out.

Steve's working on his race engines this month so I doubt I'll be able to get it in to him any time soon.

Any ideas?

[raz469]

Have you tried swapping cyl 2 sparkplug with another? 

Worth checking before splashing any cash

[AJP]

Not yet, no. Although looking again at the fault codes, the top one is 'multiple cylinders'. This is concerning me.

I'd have thought it'd only flag up multiple cylinders if multiple coils/plugs were failing simultaneously (unlikely?) or something other than coils/plugs causing misfires indiscriminately of the cylinder. I might be wrong though?

What should plugs be torqued to by the way, is it 25nm?

[fab5freddy]

I'd look at the injectors next, well known to cause problems and you've looked at the other two already. Are any of the plugs fowled?

I had faulty injector on cylinder 3, when i pulled the plug it was soaking wet from fuel, certainly not a comprehensive test but might help.

@AJP

[AJP]

I'd look at the injectors next, well known to cause problems and you've looked at the other two already. Are any of the plugs fowled?

I had faulty injector on cylinder 3, when i pulled the plug it was soaking wet from fuel, certainly not a comprehensive test but might help.

@AJP

Incidentally it had an injector replaced on cylinder 4 a few weeks ago - this was to cure a bad idle with frequent misfires at idle. At that point in time, it behaved very well under load, apart from some fuel cuts from a greedy Stage 2 map that we cured with a Loba pump.

I haven't pulled any of the plugs yet. I've got the weekend off so I think I'll have a closer look at things. One thing I did notice when I was doing the coil packs yesterday was a little bit of oil on the cam cover:



Is this a concern, and could this be causing an ignition problem?

And has anyone with misfires caused by a plug or coil had the "Random/multiple cylinder misfire" fault? I keep thinking it's significant.

[fab5freddy]

I suppose the injectors can suffer different symptoms when failing , my faulty injector was perfect on idle and toddling around it only raised it's head when under heavy load, causing really bad misfiring, obviously it was flooding the cylinder with fuel.

[AJP]

I suppose the injectors can suffer different symptoms when failing , my faulty injector was perfect on idle and toddling around it only raised it's head when under heavy load, causing really bad misfiring, obviously it was flooding the cylinder with fuel.

Yeah, if I was loaded I'd have replaced all 4 injectors with new, but instead I replaced the faulty one with a used one.

It's a tricky one to second guess. Fuel and spark demand are theoretically highest under most load, right where it's misfiring. So it could be either.

But like you say, a bad injector on 2 could well be the culprit. If one failed on 4, maybe it's logical that the others weren't far behind, albeit exhibiting different symptoms. I'd be really surprised if a 3 month old plug had failed.

It had a good check over when it had the injector replaced. Compression is good, no vac leaks etc.

I hope it's a bad plug, but deep down I just know that's far too optimistic, and unlikely. Unless something has prematurely killed the plug.

[fab5freddy]

Stranger things have happened mate, hope for you it is just a plug 

[AJP]

Cheers mate! Fingers crossed ey.

[r5gtt]

check the injectors are flowing correctly?. stupid auto correct 

[AJP]

check the injectors are glowing correctly?.

Glowing..? You mean flowing?? It's starting to look like an injector. I'll pull the plugs at the weekend and see how they look, and take it from there.

I honestly thought I had things running properly after the new pump went in. And would have bet my arse on this being a coilpack. Oh well, at least they're ticked off the list.

[r5gtt]

check the injectors are glowing correctly?.

Glowing..? You mean flowing?? It's starting to look like an injector. I'll pull the plugs at the weekend and see how they look, and take it from there.

I honestly thought I had things running properly after the new pump went in. And would have bet my arse on this being a coilpack. Oh well, at least they're ticked off the list.

Yeah flowing stupid auto correct again. I have to keep editing the posts as I forget to proof read what I've typed 
Shame you've spent loads and still in the same boat but can't be asked to get yourself a vagcom lead 

[AJP]

To be fair I did look into it and I couldn't get my head round either genuine/snide lead, cost etc. I think in all honesty it's an injector I need to be budgeting for right now! I will sort it one day though, I promise :)

I've spent 80odd quid for the coil packs. The existing ones were old anyway so in theory it's a preventative measure even though they turned out not to be the cure.

The fuel cuts are fixed. The bad idle (injector 4) is fixed. So I do feel like I'm making some sort of progress. Two steps forward one step back!!!

[AJP]

My brother's got an OBDII tool, which I'm sure is capable of reading misfires on individual cylinders, so..

Plan is to scan (expecting cyl 2 again), clear codes, pull and inspect plugs, swap plugs 2 & 3, drive to misfire, scan, pray to god it comes up with cyl 3. If not, well I'll be a bit bloody gutted.

[r5gtt]

I'll sell you some s3 injectors @AJP