S3 misfire

[paddy]

On a cold start my S3 runs on 3 cyl at 1200rpm.
Immediately the revs drop to 800rpm it cuts in on 4 and is fine. This may be after only 15 seconds on a reasonable day so its not an air or water temp sender.
Once its run for long enough for the "auto choke " to cut out its fine all day in fact its blisteringly quick right to the red line without a misfire.
Changed plugs and coil packs as they were due anyway. Fault code unhelpful, just says random misfire P0600 ( like i didnt know that)

Anyone else had this ? friend had it on his TT and never got to the bottom of it.

 

[prt57]

Have you every had the injectors checked? I realise it is only at certain revs but it could be that one injector has a partial blockage that is just good enough for most of the rev range but not at the critical point.
The fact that it is OK when the “choke” is off could indicate fuelling issues

 

[paddy]

Appreciate the thought, I wondered if it was tracking down the coil but i dont get why its cured immediately the choke goes off so i need to find what triggers the choke. its not heat because it cant possibly register the heat in 10-15 seconds unless it does measure outside temp rather than water or manifold temp..

 

[prt57]

I suggest you ask the same question on TFSI tuning Facebook.

 

[nluk100]

Injectors is a good shout, may not be able to supply the extra fuel for a cold start hence the misfire / poor running. Did you check the usual suspects i.e. PCV and dipstick as these can cause issues too?

 

[paddy]

I think injectors are ok because its running a Loba HP pump that is suppling fuel up to 7k rpm without trouble.
Dip stick and PCV would effect the whole thing i think not just one cylinder on choke.
I just got another set of plugs so will swap them and check the coil packs for signs of tracking and oil from the head gasket as well

 

[paddy]

Problem was the injectors after all
Changed all 4 problem solved. Full marks to PT, one was leaking down over night causing the misfire on startup. also found 3.5 tons of carbon on the valves

Cheers

 

[prt57]

Problem was the injectors after all
Changed all 4 problem solved. Full marks to PT, one was leaking down over night causing the misfire on startup. also found 3.5 tons of carbon on the valves

Cheers

Glad to be of service sir!!

 

[S.]

Glad you got away with it.
Got new ones or got them serviced?

 

[paddy]

bought new but not for the feint hearted as £185 + vat and fitting means about £1500 with a fuel filter and fitting
i have the old ones and i might get them serviced and re sell.

 

[ch1z64]

bought new but not for the feint hearted as £185 + vat and fitting means about £1500 with a fuel filter and fitting
i have the old ones and i might get them serviced and re sell.

Throw them away @paddy , lol

Sent from my SM-G970F using Tapatalk

 

[samisnake]

na dont throw them away, they have a value for people who are doing k04 conversions.
my friend sold his old ones for £300, although they were working fine. a refurb on them is around £150, so even if you get £100 for them its a 'cheap' buy for someone looking for injectors. get them refurbed yourself, and youre looking at selling for £3-400

 

[S.]

bought new but not for the feint hearted as £185 + vat and fitting means about £1500 with a fuel filter and fitting
i have the old ones and i might get them serviced and re sell.

Cheaper than rebuilding the engine buddy.
I had injectors shipped to bar-tek (option for us outside UK), for asnu service (similar to r-tech). Now waiting for Santa and his bag of forged parts

 

[theViTALiTY]

Were you having a cold start or it was straight drop to 800 revs as it fires up?
Mine sometimes skips the cold start for some reason, like it fires up and jumps to 1200rpm, then right away it starts dropping to 800 slowly, the same it would when the cold start would be done. However, if i turn it off when that happens, and start it right back up, it starts with a proper cold start holding 1200rpm.
It doesnt sound or seem like it missfires so it has me wondering what could be messing with it :/