Cannot Figure out Misfire

[Zackattack]

Ok I'm back.

I've been having misfires on bank 2 since last year. Initially when it happened it wouldn't stop ever and so I swapped coil pack (OEM) from cyl 5 to 3 and it followed so I replaced all the coil packs w bremi. My car is an 04 A6 quattro turbo and I do not have ICMs.

Now I started getting misfires again on cyl 5. I cut back the harness and found where the wires for this cyl were pinched at one point, more than likely by the valve cover and had been shorting out. I replaced that section of wire. Now almost a year later it's just gotten out of control. I will get a misfire once the car is fully warm (oil temp >200). It will happen under low acceleration only, like creeping through a parking lot. It will only happen on cyl 5 and cyl 6. It is not the coil packs. I have checked resistance on all coil pack wires back to ECU plug (when car was cold) got <1ohm. I now have a megaohmmeter that I'm going to meg the freaking wires for 5 and 6 with but I highly doubt there's an issue and here's why:

-Misfires happen, if I swap coil packs it goes away for a bit but then comes back on 5 or 6
- misfires happen but if I shut the car off for a little they go away, but then come back as soon as the car gets warm again only on 5/6
- Getting open circuit on 5/6 doesn't make sense because a short doesn't cause an open circuit. The car would know a ground and throw a code for that.
- There's no other codes

One thing is I know on bank 1 the VVT is going out (chain slap) and I got a new one to replace it. Right now at idle its showing -12 degrees and bank 2 is showing -1. But that is bank 1 and not bank 2 on which I'm having misfires.

Ross tech lists fuel pump relay as possible cause for P1367 (cyl 5 open circuit), why? I haven't replaced this but I might as well. I bought a new cam sensor for this side too because I'm just out of ideas.
Ross tech doesn't list P1370 however, which is cyl 6 open circuit.

If anyone has any ideas please throw them out here!

Thank you!

Zach

[V1nny]

Pull your ignition coils (label them, so you know which cylinder), and shine bright light inside deep tube, where coil contacts the tip of the spark plug. If you see anything other than a shiny contact surface, that's maybe a root cause of your misfires.

[ShelbyM3]

I second what Vinny said. Start small, if you haven’t already. If you’ve got a bad “inner” valve cover gasket it could seep oil into the spark plug recess and when the engine gets up to temp that oil is much less viscous and may be causing a misfire. Maybe!?


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[Zackattack]

Thanks but this was the first things I did a year ago. Check them every time I swap them which is about 1x per week now. It's something deeper. I'm digging through the schematic on alldata right now.

[ShelbyM3]

Touché. Have you looked into fuel injectors as a culprit at all? Is there any chance the timing could be off? Just thinking out loud to try to be helpful.


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[Zackattack]

Ok. The circuit is very simple. Terminal 30 from the battery gives power through D23 to the ECU power supply which shares it's power with the ECU as well as all coil packs. So they all get the same power feed. They are all connected together via grounding on term 85 and 131 on the R & L side of the block. So if one ground isn't there or is faulty they all don't work. Then 3 feeds from the ECU: 95, 103 & 111 for 4,5&6 and 94, 102 & 110 for 1,2&3 respectively. The power feed in for ECU relay comes directly from the battery through a 150A fuse somewhere that I haven't been able to find yet physically. It runs through terminal 30 under the dash and then directly to terminal 17 of the fuel pump relay. Terminal 30 also supplies the ECU relay. Short story is, if terminal 30 has power then the ECU has power and therefore the coil packs all have power because it's all the same harness. So why would ross tech troubleshooting say to replace the FPR?

I need to meg these wires tomorrow and see what's happening.....

[Zackattack]

Touché. Have you looked into fuel injectors as a culprit at all? Is there any chance the timing could be off? Just thinking out loud to try to be helpful.


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Unfortunately the fuel injectors work because they continue to spray fuel while the car is in "misfire mode" and then my cat catches on fire which gives me a small heart attack every time it happens. Also have ohmed out the injector wires but nit megged them.

[Zackattack]

I figured it out. It was the spark plugs. Apparently excessive idle isn't good for this heat range plug and it makes the plug too cold to remove deposits. I idle a lot being this is my winter car and I want it warm before I get in it. I only use premium grade fuel but still these plugs were coated with a hard texture that, when I put a meter on the threads and the electrode was showing open circuit. I didn't meg them but figured as the engine heated up it exacerbated the insulation properties of whatever deposits these are and even the heavy current flowing through the coil was unable to catch a ground. I guess I'll just have to change them out more frequently being how I idle a lot. These plugs are top of the line NGK and only lasted about 15-20k miles. I put in a much cheaper Bosch (made in Russia, go figure) and they're doing fine on a couple long drives.

I guess I should have listened and checked the simple stuff first