Intermittant Misfire

[bobla]

OK this may be a bit long winded but let me begin. My ABY coupe has recently developed a misfire that occurs on start up from cold then goes away after 30-60 seconds of driving, runs fine for about an hour then starts to miss again but not as viciously as when its cold. When cold it sounds really bad.
When its warm it misses only at tickover and drives ok off boost. Then when I hit boost it feels like its holding back slightly and missing now and then.

Also i fitted a set of Bosch F5DP0R's 2 weeks ago which cured it for a week or so.

I'm new to Audis so the more info the better.

Hope thats not too confusing but hey its my first post so i'll learn to keep it short in future.
Cheers in advance. Great forum by the way tons of info on hand

[Greg_S]

could be a coil pack/packs that are duff or the igintion amp. Or a number of other things, not my area of expertise im afraid though. Audiman (tom) can probably advise.

Greg

[audiman]

First things first, check the car for fault codes. See S2central.net for info on doing that. It sounds like an ignition type problem to me tho. Remove the coil packs. Are the extensions on the ends OK? Also remove the plugs and without touching the white bit, check to see if there is a black 'tracking' line down it to the metal seat area.

[bobla]

Cheers Audiman i think a guy at work has VAG fault code reading gadget so i'll give that a whirl and see what it comes back with. Ordered some NGK heat range 8 plugs yesterday as i read on here that higher boost requires colder plugs and i'm running 1.6 bar with 375bhp so uprated plugs may be required.

[audiman]

What plugs did you order? The plug debate is still an open one. Many tuners still use the OE plug at high power with no problems. I have had in the past misfire problems with NGK's.

BKR8EIX???

There is a NGK race plug, as a month ago the plug above was not yet available in the UK. But that P/N is at work

[bobla]

The plugs are Iridium tipped heat range 8 which i believe is slightly colder than the F5DP0R's i have at the moment.

In hindsight though i think it could be more to do with the coils as the current plugs are only 2 weeks old and did work fine when first fitted. Time to test the coils methinks.

Do you know of anywhere to get coils from should i need them tried main stealers and they're asking 120 quid each. Ouch!

[Doug_RS2]

BKR8EIX???

There is a NGK race plug, as a month ago the plug above was not yet available in the UK. But that P/N is at work

I have 5 of these sitting here - I am only going to try them if we have misfiring problems when I increase the boost again. Evo and Scooby guys use these specifically on high power cars for trackdays!

I had misfire problems but only on high boost. A coilpack on the way out 'usually' either totally stops working or it stops working at a high boost level.

Misfiring at idle is 'usually' the power amplifier stages - you need to work out what cylinder is misfiring at idle - then swap the power amplifiers over and see if that has changed the misfire - if it has it is the power amplifiers - if it hasn't more than likely the coilpack.

Sal lent me 4 coilpacks to solve my problem - I haven't worked out if one specific one was knackered yet - still need to do that.

If you have a DMM that measures conductance you can measure the output of the coilpacks - if one is a lot higher than the others it is most likely that coilpack.

I need to get my hands on a spark tester - you can measure how far each spark jumps - this will tell you if you have a weak spark on one coilpack/amplifier.

[bobla]

Cheers Doug it only misfires badly when its first started up on a morning but when i'm at full boost (24 psi) it misses but only slightly its still driveable off boost though.

i'll test the coils and amplifiers then and see what comes back. Just done a compression test all within 15% of each other dunno what they should be but they range from 185psi on pot 1 to 165 psi on pot 5. Thought maybe head gasket had gone but these figures seem ok.

Checked the plugs really black been overfuelling loads only been in 2 weeks. Bit of oil on no.3 possible piston rings? Any thoughts?

Just found the post with compression values i guess mine are ok lowest was 11 bar so back to the drawing board.

[audiman]

Been think about this one. Leaking injectors can make it hard to start first thing. Also if a cyl has a load of oil in it from a leaving VSOS this will foul a plug until the oil is burnt away. Its hard to diagnose this over the net, get a garage to check it out. does it smoke in anyway in the morning?

[bobla]

No smoke at all. It did start smoking slightly on saturday at tickover but it didn't smell like oil more like unburnt fuel which i put down to the misfire.

Sodding thing i knew i should of stuck with my honda never let me down. Can't beat full boost though(when it works)!