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View Full Version : Cylinder 2 Miss fire: Resistances seem in spec?



Ryanic
12-20-2018, 06:42 PM
1998 A4 2.8 30v Quattro. 220k Miles

About a month or two ago I started getting some light misfires only after the car warmed up and while I was in the 1-2k RPM range and giving it medium light to medium throttle. Replaced spark plugs, problem went away for about a month.

After the problem came back it's been getting worse over the last 2-3 weeks. Most of the time it only misfires after the cars warmed up but some days itll misfire while cold started. Only in the last couple days has it finally been throwing a misfire CEL code and its always been on Cylinder 2.

So far I have tried moving my cylinder 2 spark plug to cylinder 1 and my cylinder 1 spark plug to cylinder 2. Misfire still stayed on cylinder 2. Okay so not a faulty spark plug.
I pulled the cylinder 2 and 4 wires off the coil pack and tested the resistance. I believe cylinder 2 wire was somewhere around 4.89 and cylinder 4 wire was around 4.77. This was just the wires being tested. The coil pack for cylinder 2 and 4 was 12.28 which from another thread I believe is in spec. I switched the cylinder 2 and 4 wires around so now my original cylinder 2 wire is on cylinder 4 and vice versa. Waiting for the car to throw a misfire code again to see if the misfire moves to cylinder 4.

I have also tried using a water bottle to spray the wires and coil pack to see if I can see any arching from a damaged wire or coil pack: No luck

Thing to note at the beginning of the week I did put in some chevron techron fuel system cleaner to try and clean up the injectors (I've been using questionable 91 gas for the last 5 or so months). I'm about half way through a tank with that in there. Put this in after it started misfiring more frequently. Planning on running a second treatment through it after this first tank is over.

If the misfire moves to cylinder 4 I'll know my problem is the wire most likely but in case it doesn't follow to cylinder 4 what else could I be looking at to diagnosis this issue? I really don't want to just start throwing money at wires and coil pack etc.

Codes:
16686: Cylinder 2 misfire detected: no indication on display
16684: Random Misfire detected: no indication on display
P0302: Cylinder 2 Misfire Detected

16806 / P0422: main cat bank 1 efficiency below threshold (Have had this for a couple years now)

Idles fine while cold but once the start starts to warm up it now bounces a little bit while idling. Gets some bad stumbling when in low RPMs and giving it mediumish throttle.

Thanks

mobildetroit
12-26-2018, 09:11 AM
Cat back pressure causing misfires? Replace cat maybe?

Ryanic
12-26-2018, 09:31 AM
Cat back pressure causing misfires? Replace cat maybe?

I did read somewhere that this can cause misfires but the example I saw they were throwing misfires on all cylinders of the corresponding bank.

The misfire seemed to lighten up over the last week while I was doing fuel system cleaner so I thought maybe it was an injector but now its back again and it pretty bad. It finally threw a misfire code after switching my cylinder 2 wire to cylinder 4 and my cylinder 4 wire to cylinder 2. Going to get it scanned tonight to see if the misfire moved to cylinder 4.

Blazius
12-26-2018, 09:31 AM
Cut it out :D

Fasterd
12-26-2018, 09:39 AM
Why wouldn't you play musical packs....that always answers the question

Ryanic
12-26-2018, 10:20 AM
Why wouldn't you play musical packs....that always answers the question
Pretty sure that's not possible on the V6? Right?

https://images-na.ssl-images-amazon.com/images/I/710FiD0oeVL._SY463_.jpg

I don't think the coil packs come off of the unit? I thought I read that they were connected underneath somehow as well.

Fasterd
12-26-2018, 10:44 AM
https://pics.me.me/ha-gay-24960689.png

vrmm
12-26-2018, 02:31 PM
Hot/cold is going to play a factor in internal resistance of the coil. Resistance is heat so even if it's at spec cold once it's hot it could change. Maybe.. just a thought..

I would find a used coil and put it on. It doesn't have icm's right? That's probably what's underneath the entire coil pack if it even has that in the system, but changing the coil would be the only solution.

Fasterd
12-26-2018, 02:50 PM
^^^ 2nd the motion. Temp would dramatically affect conductivity of a device (you can hear an audible difference from an ice cold class D amp vs one on a spring day)

PZ.
12-26-2018, 03:58 PM
A bad coil would cause 2 misfires as if fires 2 cylinders. Most likely it's the wire. A bad/dirty injector tends to perform worse when it is cold. No oil on the plugs/wires when pulled? That's pretty common on the 2.8 due to valve cover gaskets leaking. A bad PCV will cause that.

Ryanic
12-26-2018, 04:42 PM
A bad coil would cause 2 misfires as if fires 2 cylinders. Most likely it's the wire. A bad/dirty injector tends to perform worse when it is cold. No oil on the plugs/wires when pulled? That's pretty common on the 2.8 due to valve cover gaskets leaking. A bad PCV will cause that.

I do have oil leaking into cylinder 1 spark plug well due to a bad valve cover gasket but no misfire there.

Had the car read for codes and the misfire moved to cylinder 4 as I had hoped. I assumed a bad coil would cause both cylinders to misfire as you said, they fire two cylinders each and i'm only getting one misfire. I'm going to try to swap out either just that wire or all 6 depending on what deals I can find and will report back.

Thanks.

Ryanic
12-31-2018, 06:49 PM
Closing comment in case anyone stumbles across this in the future. Replaced the cylinder 2 wire and all is good.