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.

 

[jsean]

I think you might be on the right path with the vacuum leaks.
We swapped the 3 spark plugs (cyl 1, 2 & 4) back to the new ones. Pulled the remaining plugs too. Everything was gapped at 0.030 (so much for NGK saying these are pre gapped at 0.036) and have now been set at 0.036” and installed back.

We found a M6x32 bolt that fits well into the valve cover and closes the gap. Did that and no difference.

Next we purchased a coil from a local parts store (made in Poland like the OE part!) and installed it for cylinder 2 since that’s the consistent one. Made no difference.

Swapped coil at plug 1 with plug 2 and still the same thing. P0300, P0301 and P0302.

One thing we noticed yesterday and today is that it sounds like there’s a lot of hissing coming from the intake manifold area around cylinders 5&6 (can’t tell for sure but that’s where it sounds the loudest).

Took a video of the car running - with and without the PCV valve hose. Not sure if the video helps any with diagnostics?

VR6 idling noise

Outside of firing the parts cannon with changing out the entire valve cover to rule out the PCV diaphragm, not sure where else to go.

All the other vacuum hoses seem intact from what we can see.

Edit: spark plugs 2 through 5 were all pretty black and carboned in the 10ish mins of idling total thing has had since yesterday, after the job.

 

[JDenyer232]

Take a propane torch, don't light it, place the nozzle at the intake manifold where you think it's leaking. Open the torch valve and let a little propane escape. With your scan tool watch the live data for the short term fuel trim. When you see a fairly drastic change that's where it's leaking. Also listen for a change in the sound of the engine. Do this to check all vacuum lines as well. What is the STFT and LTFT? That will help determine if the engine is running lean from a vacuum leak. This sounds like a vacuum leak to me.

 

[i6pwr]

I haven't torn into a VR6 yet, but a few things come to mind. Did you use a blow nozzle with compressed air and clean around the plug wells before removing the plugs? Hopefully you didn't drop any debris into the cylinder and this would be worst case but not likely.

Here's some questions....please bear with me as it's lengthy.

Where is the bolt broken? Can you remove all of it? If so, do you have an ACE hardware or similar to match up the threads and length, maybe vary length with a few washers or bushings for the time being?

If you can remove it maybe swap bolts from another location near the middle.

I assume you had to remove the intake to get to the valve cover? If so, what gasket did you use, also did you reuse any of the old gasket.

Does it have replaceable seals around the bolts?

Did you spray the motor with water or get the plug terminals wet?

I would take a vacuum gauge and make sure the needle is steady while idling, this will ensure the intake valves are sealing and no debris fell in. Also take an envelope and hold against the exhaust flow, if it stays folded over from flow and not SNAP back to the tip, then the exhaust valves are sealing.

I'm going with a large possibility of poor sealing of the intake with unmetered air, maybe from a bad gasket, old gasket, missing gasket part, etc. Also, did you disconnect any of the coils with the engine running? Sometimes this can ruin a coil.

Did you disconnect the throttle body? Some VW's are finicky with needing a TB re-adaptation if connector is removed, along with a battery disconnect but not as likely here.

 

[i6pwr]

We found a M6x32 bolt that fits well into the valve cover and closes the gap. Did that and no difference

Sorry, I missed this part earlier.

 

[RooflessVW]

Did you break the coil connectors? Pretty common.

 

[jsean]

Take a propane torch, don't light it, place the nozzle at the intake manifold where you think it's leaking. Open the torch valve and let a little propane escape. With your scan tool watch the live data for the short term fuel trim. When you see a fairly drastic change that's where it's leaking. Also listen for a change in the sound of the engine. Do this to check all vacuum lines as well. What is the STFT and LTFT? That will help determine if the engine is running lean from a vacuum leak. This sounds like a vacuum leak to me.

This was a great suggestion, except I’m a little paranoid with torches! So I instead used brake kleen. Turns out it was the intake manifold gaskets that we had installed new from RockAuto (Elring brand).

Odd, so switch it back to the old ones and sure enough, car runs like a top. Took us a couple of attempts to get it right with seating the old gaskets back right in terms of the bolts tightening pattern.
We took it for a quick spin (about 15 miles) and it ran like a top. No more codes.

 

[jsean]

Did you break the coil connectors? Pretty common.

Good suggestion. Couple of latches were broken by the prior owner when they installed the Bosch plugs. We were careful with all the plastic stuff except for the little cover that goes over the ignition coils wire harness.

It was partially broken before got into the job and well, we fully broke it

Turns out the Elring gaskets are much stiffer and didn’t compress as much as the old VW ones on there? So we swapped them back and all’s good now.

 

[jsean]

I haven't torn into a VR6 yet, but a few things come to mind. Did you use a blow nozzle with compressed air and clean around the plug wells before removing the plugs? Hopefully you didn't drop any debris into the cylinder and this would be worst case but not likely.

Here's some questions....please bear with me as it's lengthy.

Where is the bolt broken? Can you remove all of it? If so, do you have an ACE hardware or similar to match up the threads and length, maybe vary length with a few washers or bushings for the time being?

If you can remove it maybe swap bolts from another location near the middle.

I assume you had to remove the intake to get to the valve cover? If so, what gasket did you use, also did you reuse any of the old gasket.

Does it have replaceable seals around the bolts?

Did you spray the motor with water or get the plug terminals wet?

I would take a vacuum gauge and make sure the needle is steady while idling, this will ensure the intake valves are sealing and no debris fell in. Also take an envelope and hold against the exhaust flow, if it stays folded over from flow and not SNAP back to the tip, then the exhaust valves are sealing.

I'm going with a large possibility of poor sealing of the intake with unmetered air, maybe from a bad gasket, old gasket, missing gasket part, etc. Also, did you disconnect any of the coils with the engine running? Sometimes this can ruin a coil.

Did you disconnect the throttle body? Some VW's are finicky with needing a TB re-adaptation if connector is removed, along with a battery disconnect but not as likely here.

Lots of good questions. I’ll try and answer them in order:
1. The prior owner had broken off the one captive bolt in the upper intake manifold. Neighbor didn’t do anything about because it was running fine. The broken off stud was on there real tight (almost as if someone gooned it righty tighty). So we got that broken bolt off and replaced it with a M6x32 from the hardware store. Looks like a sore thumb, but it’s functional.
2. We installed new VCG (FelPro) and intake manifold gasket (Elring). My best guess based on non calibrated fingers is that the Elring gasket is much stiffer than the old VW gaskets. We swapped these back to the old VW ones and that car runs smooth!
3. The bolts in the manifold are captive, they back out till they’re loose - but they don’t come out. No gaskets except for the 6 square gaskets that go in for each of the runners in the manifold.
4. Should’ve thought of using water. We ended up using brake kleen to find the leak in the manifold gasket. Sprayed it around the air intake hose and the PCV hoses - those didn’t impact engine idle speed.
5. You were on the money about a bad gasket - it was the new Elring intake manifold gasket in this case. We did pull all the coils and even bought a new coil to rule out the possibility. Made no difference.
6. Didn’t have to take off the TB thankfully. One less thing to worry about.

 

[shortyb]

Strange about the difference in manifold gaskets. Elring is one of the larger OE gasket/o-ring suppliers for VAG.

 

[JDenyer232]

Glad you got it sorted out. Thanks for letting us know the outcome.

 

[jsean]

Strange about the difference in manifold gaskets. Elring is one of the larger OE gasket/o-ring suppliers for VAG.

I’d agree. I’m no expert but outside of the new gaskets from RA being defective somehow, I’m not sure what else could be the cause. The seals have specific placement positions that align orientation and depth in the intake manifold itself.

 

[i6pwr]

Glad you figured it out!

Should’ve thought of using water. We ended up using brake kleen to find the leak in the manifold gasket

Actually the water question was ruling out possibly shorting out a circuit if you hosed down the motor and not blow the liquid from some of the terminals.

Awesome you have it running good again