A4 GH05T

First time posting, I searched forums and can't quite find answer.

Background: I bought a 2004 A4 1.8t used that checked out fine. Weeks later it began to shake and sputter under acceleration, no CEL.
Come to find out during emmesions test, that the CEL would not turn on at all and that there were several codes stored.
Random misfires on cylinders 2 and 3, and secondary injection air issues.
Took it to an Audi shop where they determined the head gasket was BLOWN.
I did the repair myself using some guides and got the car started back up without incident. Got the oil changed and has all other fluids replaced as well.
It was been 4 days and the CEL came on, random misfires on cylinder 2 and 3.
Anybody run into this problem?

lyleswk

Did you ever do anything with coilpacks or plug wires?

A4 GH05T

Replaced everything that came in head gasket kit from ECS tuning, head bolts, thermostat housing, new NGK double plat plugs, and new coilpacks. I did not change the plug wires, the mechanic who diagnosed the blown head gasket told me that the wiring harness is hard wired and can't just be replaced. Any truth to this?

lyleswk

Not sure what is meant by "hard-wired" on a car. I assume you double checked all the connections you made, although if you had misfires before and after, not sure that is the issue. When you removed the head, did you have it reworked?

A4 GH05T

Did not get it reworked. I didn't see any signs of warping. Made sure the contact surfaces were clean before reassembly. All connectors good.
Last night swapped #1 coil to #3 to rule out coil pack failure, misfire stayed in cylinder 3. Spark plug was clean, not burnt, no oil, no coolant.
As for the wire harness, when I had a japanese car you could change the leads by unplugging them and simply replacing. Looked on the forum and for this car I'd have to buy the kit and cut and splice in the new connectors. I think that is what he meant by hard wired into the car, not as easy.

Could it just be a faulty connector to the coilpack?

lyleswk

Assuming your head is really straight, then about the only option you have to start shooting wires and see if you can find a bad wire or connector. That is a very tedious item which I have only once been successful in diagnosing an electrical problem in all my dealings with my "fleet" of old cars. Some people easily understand electrons; I don't. Maybe others on the forum can give you a more clear troubleshooting path. You also might try Audizine. You will get all sorts of inputs, but there is one poster over there that is called "Old Guy" that is really good at this sort of stuff.

A4 GH05T

Dove in and cut apart the rubber boot on coil connector #3 and it is a MESS. The insulation is cracked and gone on all 4 wires and they are all touching.... very likely the source of the problem on cylinder 3. I am getting the Audi A4 Ignition Coil Connector Kit by Karlyn and replacing all 4 because if #3 is this bad, I am sure the others aren't in much better condition. Thank you for the advice and input Lyle!

A4 GH05T

It's been a few weeks now and cylinder 3 is still causing problems. Since my last post I changed out the wiring to all the coil packs, checked the injector wiring, removed and cleaned the injectors, and even switched injector 1 with 3... cylinder 3 still misfiring at idle. Under acceleration or just cruising above 1200 rpm she purrs. At idle, she sounds really rough. What's left to check?

Prospeeder

I have never seen a 1.8t with a blown headgasket. I would bet its still misfiring because the headgasket wasnt the problem in the first place. Also if its always number 3, the crankcase breather parts, such as the PCV valve or its plumbing will break and create a big vacuum leak, the vacuum feed for that whole system is from a pipe right by the throttle, and it will cause a huge lean dump right into number 3. It can dilute the rest of the mixture and cause all sorts of misfires at first, but the more its driven it will richen itself up as much as possible. That may be why it missed alot at first, then as you drive it its only number 3 because it cant richen it up any more. Yes it will idle like garbage with a huge air leak from the breather parts.

A4 GH05T

I'll check for vacuum leaks. When reassembling I didn't notice any cracked fittings, hoses, or PVC parts.

Attached pics of the old head gasket... definitely blown, reason unknown...
Always wanted an A4 quattro, I heard they were a hoot to drive, but this one is sucking the fun out it...