Misfire's back...

**cherry1809** · Tuesday 12th March 2013, 10:16

Fitted new plugs, leads, cap, arm and changed the coil a while back, as it had a bit of a misfire. The old plugs looked fine, I.E. not sooty or glazed etc.
It ran fine until the other day and now it's intermittent misfires returned. Outside temps not making any difference, nor how long it's been running.
Only thing I haven't checked is the fuel filter. Changed the pump to a Walbro too. Any ideas?

**T5frankie** · Tuesday 12th March 2013, 11:47

Running high boost eats plugs

**cherry1809** · Tuesday 12th March 2013, 13:40

In 6 weeks?

**mike 850** · Tuesday 12th March 2013, 16:28

is it mapped? are you using crap fuel? i had a misfire but stopped when ran on optimax

**cherry1809** · Tuesday 12th March 2013, 17:34

Been using Tesco Momentum since I had the car. Only lately(ish) it's been doing it. It doesn't feel like a definate misfire, more like it's retarding too much or similar. Noticed on the way home when it does it, if I hold half throttle but still enough to boost, there's a slight screech coming from somewhere.

**stribo** · Tuesday 12th March 2013, 18:31

Could it be an injector? either dirty, or just giving up?

**T5frankie** · Tuesday 12th March 2013, 18:45

any of the plugs getting wet with oil?

**Brett855tdi** · Tuesday 12th March 2013, 19:39

Yeah i would check the plugs... just double check you cant see anything going on.
im guessing a crank sensor would throw a light?

**cherry1809** · Tuesday 12th March 2013, 23:07

Plugs fine (as were the old ones

)
Might be worth changing injectors. Any upgrades that will work okay with the 16T and a Rica 304?

**JamesT5** · Wednesday 13th March 2013, 10:31

Originally Posted by cherry1809

Fitted new plugs, leads, cap, arm and changed the coil a while back, as it had a bit of a misfire. The old plugs looked fine, I.E. not sooty or glazed etc.
It ran fine until the other day and now it's intermittent misfires returned. Outside temps not making any difference, nor how long it's been running.
Only thing I haven't checked is the fuel filter. Changed the pump to a Walbro too. Any ideas?

I had misfire issues back last year and I was tearing my hair out over them. It's possible that if the problem is still there you have a second coil pack playing up because once one starts to go it puts extra pressure on the others and it's not unusual for a second coil pack to go. Read your codes again to see.

Also, it's possible to accidentally damage the wiring around the coil packs when screwing the ignition coils back in to place to have a look for damaged wiring - it can cause a short or an earth and then it disrupts the power supply to the coil causing a misfire.

I had both of the above problem and once I fixed them the car has been fine ever since.

Regards

James

**cherry1809** · Wednesday 13th March 2013, 11:51

T'is an 850, only 1 coil

**lance** · Wednesday 13th March 2013, 12:03

Do they have a fuel pressure sensor on them I had occasional misfires and coughs splutter and iratic idle first about 3 coil packs went down followed by a boost pipe coming off followed by the fuel pressure sensor now fine no faults hiccups coughs or splutters sometimes a misfire isn't ignition linked

**960kg** · Wednesday 13th March 2013, 12:10

If it helps ?....i use Shell Optimax all the time until my local Shell garage was having an overhaul so was closed. I went to Tesco and put in Momentum and noticed i get less to the gallon but it starts so very quickly instead of just normally, even in this cold weather.

However i noticed on boost at half throttle exactly the same as yourself a slight screech and the boost guage was badly fluttering. The screech i have only had since i turned up the actuator and when i lift off at full boost 20psi so i believe it`s too much for the turbo or the Yellow spring in the Forge recirculating valve is too strong although i have an HLM 304 map??????.......i am thinking of putting back the original diaphragm as it worked well even at 160,000

Have you Volvo Plugs fitted as these are well known to be best for turbos?

**cherry1809** · Wednesday 13th March 2013, 13:00

No I went for 'upgrades' ... can't for the life of me remember what they were now. Lol. Think they're the newer NGK iridiums. Thinking back, it was missing Tuesday morning on the way into work. Stopped and filled up (Momentum) and it was fine after. Also there's puffs of unburnt fuel when it does it.

**960kg** · Wednesday 13th March 2013, 15:37

Have just been reading all about turbo squeals on Audi turbo sites and the most interesting is this which fits in nice to all that have had remaps and have these squeals.....

'Cavitation, harmonic resonance caused by the air flow being disrupted. This is happening due to a lack of volumetric effeciency either on the compressor side or the turbine side of the turbo, as we know these turbos are limited by the intake and outlet to and from them'

and

'...the noise you're hearing is due to 'cavitation'. This is the point at which the turbo runs out of puff basically and cannot push air any faster. The noise itself is turbulence in the intake caused by the compresser wheel. It can be fixed by turning the boost down a couple of settings... however this will make less power. Any glitches that are felt along with this noise are most likely down to intake pulses caused by cavitation.'

From what Bill at Badger 5 tells me its common on K04 turbo'd cars as remapping takes them near to the limit of their airflow capabilities. Mine does the same, not all the time but it does do it. Only real solutions is to back off the boost or maybe go hybrid turbo but from what I understand, most of the flow restrictions on the S3 are to do with the exhaust manifold as its a very poor design. Better manifold and downpipe will help here but its expensive and there isn't any real power gain to be had although the engine does breath better as a result... so I am told

**markst5** · Wednesday 13th March 2013, 17:20

I have this problem now and then.......usually when it warm since I put denso TT plugs in :/ I've changed the leads/dizzy and arm!! Was thinking it is the new plugs and maybe coil going??

**cherry1809** · Wednesday 13th March 2013, 17:40

Can't be the turbo running out of puff, only does it on half throttle. Never heard of that either

I'll try changing the injectors, it'll be a cheap upgrade as long as they're okay with the mods I have at the minute. If that doesn't work it'll be a start at the beginning job I think.

**woz** · Thursday 14th March 2013, 23:01

Originally Posted by cherry1809

Can't be the turbo running out of puff, only does it on half throttle. Never heard of that either

I'll try changing the injectors, it'll be a cheap upgrade as long as they're okay with the mods I have at the minute. If that doesn't work it'll be a start at the beginning job I think.

I Just got rid of my misfire - changed the injectors!!!. 50% better consumption around town(was 18 now 26), 10% better on a run(was 28 now 31) and NO misfire on boost. They are not even cleaned yet and one has a cracked seal on it. I simply got a sirty old set of whites for £20 to replace the orange ones) Its probably paid for itself in a trip to Cornwall and back.
Woz