Odd misfiring and codes on a VW VR6

[jsean]

Neighbor’s vehicle - 2012 Passat 3.6 with about 100k miles. He needed help with a leaky valve cover gasket and we figured change the spark plugs out too while in there.

Removal and install was straight forward with the help of some beers. Car ran awesome before the work and we scanned it to verify no codes before starting the work.

Someone had installed Bosch plugs in there and they didn’t both cleaning the valve cover beforehand. So we ended up having to vacuum out the crud the best we could (after we had pulled plugs already). Cylinders 1, 2 and 3 were filled with oil from the older leaky gasket.

Powered it on. It ran very rough and it gave P0300, P0301, P0302 and P0304.

Switched cylinders 1, 2 and 4 back to the old Bosch spark plugs and no difference.

Switched coils 3 and 4 and coils 1 and 6 about 2 hours ago. Haven’t gotten P0304 since then.

But we are still getting P0300, P0301 and P0302 once and then after clearing the codes it went to just P0300 and P0302.

Ok, so we switched coils 2 and 5. And we are back to having P0300, P0301 and P0302.

There’s a broken upper intake manifold bolt by runner #2 and it’s been been that way since he bought the car about year ago.

But I don’t think that could be the cause? VW doesn’t sell the bolts - gotta buy the whole manifold for $1000ish or about $300ish used.

Both of us really confused now what’s happening.

In summary:
1. Swapping plugs back to old on misfiring cylinders didn’t change the codes.
2. Swapping coils 2 and 5 kept the code at cyl 2.
3. Swapping coils 1 and 6 removed cyl 1 misfire for a bit and now it’s back on cyl 1.
4. Broken bolt on cylinder 2 intake manifold runner - could that cause the problem?
5. Maybe bad PCV? I’m not sure if these fail spontaneously though given that the car ran great before the work?

 

[JDenyer232]

Maybe the coils were damaged from the oil and removing them was the last straw and now they are flakey. Just a thought.

 

[Speedbird001]

- Respect for helping out a neighbor with a not small and potentially scary job like this (Karma)
- Always liked the VR6, my dad had similar car, very nice
- FWIW, I did this kind of work on a Daimler vintage Grand Cherokee... Seemed simple, but opened up a can of worms.. ended up uncovering DIRTY/~80% plugged PCV system, filthy throttle body, MAS and intake and promptly fouled the plugs (That an Italian tune-up could not fix). Ended up cleaning all of the above, replacing 2 (Disintegrating) PVC system hoses and new plugs.... After that and a ECM relearning session it ran like a top once again. Point is, might have to go thru a whole tune-up regimen.

 

[jsean]

Maybe the coils were damaged from the oil and removing them was the last straw and now they are flakey. Just a thought.

Honestly, at this point I’d rather it just be the coils than anything else. What throws me off is if it were coil, shouldn’t the codes follow the coil instead of being stuck at the cylinder?

 

[jsean]

- Respect for helping out a neighbor with a not small and potentially scary job like this (Karma)
- Always liked the VR6, my dad had similar car, very nice
- FWIW, I did this kind of work on a Daimler vintage Grand Cherokee... Seemed simple, but opened up a can of worms.. ended up uncovering DIRTY/~80% plugged PCV system, filthy throttle body, MAS and intake and promptly fouled the plugs (That an Italian tune-up could not fix). Ended up cleaning all of the above, replacing 2 (Disintegrating) PVC system hoses and new plugs.... After that and a ECM relearning session it ran like a top once again. Point is, might have to go thru a whole tune-up regimen.

Thanks, I try and help neighbors out where I can. Folks are working hard to make their money and shops just seem to be getting more expensive as the years go by.

I’m going to try plugging the PCV breather tube tomorrow to see if it makes a difference. I’m also having him go to the hardware store and see if he can find a bolt with the correct thread diameter to see if clamping the hole down at runner 2 will help some.

If those don’t fix the issue, I’m not sure where to even troubleshoot.

 

[Speedbird001]

I'm a rookie, but don't see how plugging a system will help in the long run... YMMV: Two different older cars I help get squared away; a V8 Grand Cherokee and a 90's Saturn; both had jacked up PCV and intake systems. Both required a good bit of carb cleaner, elbow grease, new valve and a few replacement hoses (Because the existing ones were plugged and crumbling). I felt like the dirty PCV system was "Fouling" for lack of a better word other parts of the engine. Coincidence? Both had filthy throttle bodies, intake tracks, MAF sensors, PCV valves that did not jiggle and PCV hoses nearly plugged shut with carbon and wet/black/oily stuff.

Finally, on both, once I had them cleaned and tuned up and running good I had to disconnect the battery for a minute then go few miles, cycles or whatever for the CEL to go off and stay off.

Best of luck to you. Keep up posted; everyone loves a good victory story.