hey guys, my 1.8T every time I drive it cold or hot, as soon as it gets over 3000rpm it misfires really badly in any gear, to the point the car refuses to accelerate and I have to upshift.  I did check the compression of the cylinders and it read over 200psi, so thats not the issue either.

 

The coil packs I doubt because from previous burned coil packs I would expect one of them at least to go off completely and the car idles rough, that is not the case though.

 

The other info -  which I doubt is the issue - is the exhaust manifold that has two huge cracks.

 

The injectors again I doubt because I would expect under heavy load if it is rough at 1st gear and 3000rpm I would expect to go rough on 2nd at 2500rpm

 

Have I changed anything lately to the car? No.  I did take the starter out, cleaned it and put it back on.  Not sure if there is another grounding point for the coil pack apart from the one right next to the coilpacks.

 

Any thoughts?

in case someone says injectors, I exchanged injector from cylinder 1 with cylinder 3, the car is still misfiring on 3 or 2, depending on the mood.  Everytime I logged the car it is always cyl2 or cyl3 that keeps misfiring

What happens if you swop cylinders 2 and 3 coil packs with cylinders 1 and 4?, does the misfire move with the coilpack?.

 

Is there any damage to the coilpack loom insulation itself near the plugs to coilpacks 2 and 3?.

Edited 18 January, 20179 yr by kentphil1

What happens if you swop cylinders 2 and 3 coil packs with cylinders 1 and 4?, does the misfire move with the coilpack?.

 

Is there any damage to the coilpack loom insulation itself near the plugs to coilpacks 2 and 3?.

I had swap 1 with 3 but nothing changed, I ll swap 1-2 and 3-4 to see if that changes anything

 

I have checked the cables etc but nothing visible... I ll check again

Someone had a similar fault on here before that they couldn't trace, until it eventually fired up a fault code. Replaced the coil packs and it solved the problem.

Based on that you'd suggest coils or the wiring

Cracks in the manifold could be a potential cause, depends if they are deep enough for it to blow though, any signs of exhaust soot around them? If so, then as the engine speed is increasing, so is the fuelling, the o2 sensor in the exhaust is seeing the mixture leaning off due to the air leak, and adding more fuel to compensate, this could be leading to the misfire. Have you taken the plugs out and checked them? Black and sooty would indicate an over rich mixture.

Also check for vacuum pipe leaks under the manifold, although these usually throw up a fault code for mixture lean bank 1 for example.

I'd agree that an actually cracked through manifold could be the cause.

 

Other thoughts would be bad spark plug(s) (How long since they were last changed?) or a collapsing or cracked vacuum hose (needs physical inspection by hands, not just visual since you can't see some of the places where cracks occur, or where an externally fabric reenforced hose is collapsing internally and will feel soft if squeezed).

exhaust manifold indeed has soot, I can see it clearly.  You might be right there actually, it did not occur to me regarding the o2 sensor reading less.  I guess a test would be to fully un-tighten the wastegate, drop in a green spring into the 007 and see if at least the misfires are happening at higher rpm even if that shifts 500rpm it would be enough.

 

spark plugs the ones I took out were absolutely fine, I checked against several guides in google.  The new ones went in but still same issue.  

 

Re vacuum hose, I just replaced a split one but the issue was happening a long time before that.  The rest of them dont seem to be split or broken as I had an issue 3 years ago and replaced one that was ripped.  if there is a rip somewhere big enough to let a lot of air out I believe I would hear it whistling - as I did with the one I replaced

 

I tend to believe it is the mani as back in September I came back from the lake district, on the way back I was going quite fast (embarrassed to say how fast) for over an hour.  Shortly after that trip I began seeing those issues...

 

The only thing I want to make sure is there is nothing wrong with the wiring of the coil packs.  Not sure where all these wires end up, I think they go somewhere behind the gear cables...

Ah, the issue with the spark plugs would have been the insulation breaking down at high revs after being very hot, rather than something you'll find in the "plug faults" guide. If you've fitted new plugs it's unlikely to be that though.

Any fault codes?  I have had a coilpack go bad, only showed itself under hard acceleration, normal driving was OK.

no fault codes whatsoever part from the misfires.

 

What I did was, I took out the blue(hard) spring and replaced it with the green(soft) one in the 007 DV, I undid the wastegate a little so the screws are back in their original position, and finally I decreases the boost, timing and fuel with SPS3.  I went for a ride and right away the car was behaving a lot better, it does that rough thing only under heavy acceleration. Therefore i tend to believe I need to replace the exhaust manifold - as weird as it sounds.  But I guess what the fella said above makes absolute sense where regarding the o2 sensor.

 

Any other thoughts?

I've a standard manifold for a KO3s turbo already off the car and going spare which I've inspected and appears to be without any cracks or other problems. PM me if you want to know more.

Id potentially swap all the coils out if you know someone nearby first

Leeboy I 'd be going for an aftermarket one, I still remember the smile I had on my face when I had it in 3rd after 3500rpm. No way I am putting on a factory one but thanks for letting me know

Liverpool-lad first things first. I d be doing the mani then the R8s ;)

Id be swapping the coils for a known good set before you tackle the manifold just in case!

Mani needs to be replaced anyway, even if the issue is only with the coils

Does sound like coils to be fair, when mine went it was only on harder acceleration. 

I swapped them around but nothing change.  I swapped injectors around but then again nothing changed, always cyl2 or 3 misfiring.  Now the car has gone nearly a week with the green spring and all the settings lowered with SPS3, car is totaly different and will only misfire if I go very hard on it.  Before it would misfire very easily.  Green spring plus untightening the waste gate means a lot of the gases now can escape properly and in return the pressure is lower.   But thanks for your inputs.  When I change both mani and coils I will update this thread.