Cold misfire cylinder 3...help needed please?

[ketteringfluff]

Please please can someone help me i have a a3 1999 with the agu it has a missfire when cold only on cylinder 3 i`ve changed coils, plugs , acu ,coil control unit , lambda`s ,temp sensor basicaly been to 5 garages plugged in with no fault codes whats doing my head in is after about 10 minutes of driving the car the engine sort of coughs and she`s away like there was nothing wrong , if i turned the car off for 10-20 minutes and started it back up the problem is back ive spent 500 quid now and all i`m getting is "we dont know whats wrong with it" next step for me is to remove the head dont really wanna go down that road until i really have to can anyone help please i`m in the northamptonshire area i`d en bring it to someone to see what they think and also its been with r tech in hinckley and even there stumped. i am a mechanic i`m now thinking damaged piston or a valve/follower problem talk to me someone please theres no way i`m selling it i love it to much.

 

[Broken Byzan]

Head gasket leak. Its water getting onto the plug electrode causing the miss, when it warms up the water evaporates and the spark can get through as it were.

I has this on my old Cav, run the fluid through the tank, i bet there is Co2 in there.

Are the pipes under pressure?

 

[ketteringfluff]

hi there thanks for reply i`ve also had compression test done and was all fine the car dont lose any water nor any water in the oil the only thing i haven`t mentioned when i misses you can hear a popping for the back box with tells me in on the exhaust side and not the inlet just so annoying as the car runs real nice after 10 or so minutes to be honest thats why i dont wanna rip the engine apart just yet..

 

[<tuffty/>]

Check the wiring to the coil packs. The insulation has a tendency to shrink and fracture under the heat and you may find that you have wires touching...

This was mine...

<tuffty/>

 

[abdus]

AGU? might well be the ignition amplifier. It is always cylinder 3 that will be the problem.

it's on the top side of your airbox.

 

[abdus]

and this is how to test it, very easy to do it.

http://forums.audiworld.com/showthread.php?p=1535031

BTW, it won't show any fault code even on vagcom. (well mine didn't)

 

[Broken Byzan]

I thought he said he changed that as well as all associated electrics. I know on the AEB engines it's cyl 2 that goes first, must be different for an AGU

 

[badger5]

i dont see you saying anything about the injectors?

 

[ketteringfluff]

Hi guys thank you for the replies but yes i`ve changed the ignition amp think i said it was a coil control unit ive also had the wiring to the coils checked but as i say after 10 minutes from driving from cold it runs like a dream like there nothing wrong with it, ive again been told it could be a damaged piston or ring thats sealing when hot but leaking when cold but i have done a compression test and was all fine even the lads at r tech are scratching there heads time to cut my wrists i think lol

 

[ketteringfluff]

hi yes all the injectors swapped by r tech still to no avail i cant think of anything else to do apart from stripping the engine

 

[Keeno]

I second the headgasket suggestion. Sounds like the right symptoms...