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Engine builders VW 12valve VR6 misfire...stumped.

blackohio

Generous jaywalker
Mar 12, 2009
2,773
122
Hellafornia. Formerly stumptown.
So Mitch and I did some testing. Car has mk4 headgasket, autotech 268º cams. Misfire has existed since engine went in (when cams/headgasket happened)

Wiring is good, we have continuity across the harness. Front cylinders compression was over 200 across the board. They were all right around 210

Leakdown revealed 90/85 cylinder 1, 95/90 cylinder 3 and 95/90 cylinder 6. Theres a 1% leakdown on 3 and 6 and about 5-6% on cylinder 1. Not terrible but its showing some leakage on cylinder one.

Now here's where it gets interesting. Cylinder 1 is a bit wet with what appears to be oil. Not alot but a little. Air is not leaking from overflow bottle, at tailpipe, oil cap or throttle body/egr/valve cover. The slight leak appears to be at piston ring. It's holding steady when under air but is a bit low so it's obvious theres a little leak.

Could the misfire come from a bit of oil blowing past the rings? We also heard a bit of clatter from the cylinder 1 side of the engine. Possibly the misfire slapping the valve closed or popping off it?

right now were gonna swap injectors/test them before we look at rebuilding the bottomend.

any insight?
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,031
5,921
borcester rhymes
first thing: try it NAO

Second: did you check the plugs? they may be fouled from the oil. I chased an ignition problem like yours in my ****ty audi and it ended up being the plug, not the coilpack. I suggest going out and getting new plugs regardless of make to see if that fixes it. A lot of those things are made in china now where QC is nonexistant.

Finally...stupid Q, did you possibly swap the ignition wires?
 

blackohio

Generous jaywalker
Mar 12, 2009
2,773
122
Hellafornia. Formerly stumptown.
plugs are good. test light indicates ignition pulse on each cylinder is good and consistent. Plug wires are brand new ass are plugs.

what's alarming is the oil(or what appears to be) in the combustion chamber. Ignition or electrical controlled misfire you wouldnt see that. I guess im just in denial of what the issue appears to be. Rings.
 

Sandwich

Pig my fish!
Staff member
May 23, 2002
21,031
5,921
borcester rhymes
just do me/you a favor and try swapping out the plugs either cylinder-cylinder or with a new one from the box. I've read of multiple issues with people installing brand new plugs which are already bad.

Just say no to china.
 

blackohio

Generous jaywalker
Mar 12, 2009
2,773
122
Hellafornia. Formerly stumptown.
just do me/you a favor and try swapping out the plugs either cylinder-cylinder or with a new one from the box. I've read of multiple issues with people installing brand new plugs which are already bad.

Just say no to china.

Actually that's been done already several times. Swapped plugs/injectors to see if the #1 Cylinder misfire follows it, and it doesnt. :(
 

golgiaparatus

Out of my element
Aug 30, 2002
7,340
41
Deep in the Jungles of Oklahoma
If it's a true misfire, just work your way back from the plugs and eventually you'll find your problem.

If you have a VAGcom find out if the problem is with the cylinder in question. If it is that one 100% of the time, then I'd say that you have an issue that you need to address inorder to correct the the firing problem (I doubt this is related to compression loss, but it sounds like you need to address it regardless).

How new is this motor?
 

golgiaparatus

Out of my element
Aug 30, 2002
7,340
41
Deep in the Jungles of Oklahoma
Misfire is only on cylinder 1 and if timing were off it would be all over the place
LOL! I really need to read whole threads before responding.

SInce it's with that cyl only I'd say you're issues are probably related, or it's a hell of a coincidence. Still I'd work my way back from that plug, and also check fuel supply and hope I found something. If not... time to get oily :(
 

blackohio

Generous jaywalker
Mar 12, 2009
2,773
122
Hellafornia. Formerly stumptown.
vag's not really leading us anywhere. Random misfire Cylinder 1.

So far heres what we know.
Ignition is good.
Plug is good.
Spark is good.
Timing is good.
Plug wires are new and good.
ECU is new and good.
Fuel is fine.

Motor came out of a friends show car. I think it had about 60K on it. Motor went in, cams and headgasket went in, misfire happened. Head came off got ported and polished and checked over. Misfire still exists. No compression loss at valve and no leaking of headgasket. Oil/coolant look great.

The only thing im uncertain of is the bottom end. I know the car it came out of was supercharged but barely got driven. Mostly trailered. So it certainly could be a ring.

Were gonna pull the injectors, check spray patterns and swap them around this week to just double check that, otherwise its time to get messy.
 

kazlx

Patches O'Houlihan
Aug 7, 2006
6,985
1,957
Tustin, CA
oil blowing by and fouling plug?
That's my vote. Tell-tale sign when you are only having issues in one cylinder. Oil wreaks havoc when it starts blowing by the rings. I learned my lesson the hard way about putting motors in without checking them. At the very least, I would always hone and re-ring, but 302s are a little sloppy to start with...definitely no VW expert.
 

drkenan

anti-dentite
Oct 1, 2006
3,441
1
west asheville
I'd do a compression test and see what happens. My S4 had low compression on 2 cylinders (before I sold it) and I put some oil in there, cleared it right up. We all know what that means. :(
 

blackohio

Generous jaywalker
Mar 12, 2009
2,773
122
Hellafornia. Formerly stumptown.
Compression is surprisingly good on the 3 front cylinders. 3/6 were at 210 and 1 was just a little below. I think it was 200. It was 185 at first but we forgot to rotate it to tdc. Once rotated back compression was back up to like 205.

We're both leaning towards rings, just wanted some back-up opinions before I gut this bitch. It's been almost 5 years since the cars been on the road. It lived for 3 in my garage with a seized motor. Smashed the oilpan and seized it. Then it lived at my mechanic's for 2 years as he put a motor in, problem occurred and he tore the motor back down.

The combustion chamber is certainly a bit wet, but that could be partially due to the misfire as well as some blow-by.

ugggh.
 

wreckedrex

Monkey
Feb 8, 2007
137
0
Fremont, CA
Ran into a similar problem with my brothers 1.8t and it turned out the ignition control module took a dump. Bad misfire on cyl one that didn't follow the coil pack and didn't go away when we replaced the plugs. Apparently its (another) common failure on the 1.8t, not sure if it even exists on a vr6.