Misfire - Wet Spark Plug on Cylinder 3, But Cylinder 4 Low Compression...

[BMWahba]

Alright boys, need some help to ease my frazzled nerves.

My car is a garage queen, I have driven it a total of *maybe* 3,000 miles in the past 4 years. Well, long-story short, I took the car for a drive about 4 months ago after it sat for a period of maybe 2-3 months, and it developed a misfire. I noticed it under load, and at idle.

At that point, I only had a check engine light when it would miss under load. So, I chalked it up to bad coils. I ordered 6 new coils, but before installing them, I drove the car one more time to see if it was still doing it, and it had completely cleared up. Ran beautifully, no misses, no stumbles.

Parked the car, sat for about another month and I decide to drive it again. Well, she ran absolutely horrible. Was misfiring a lot at idle, threw a check engine light (at idle). At this point I am panicking, and decide it's time to tear into it to see what is going on.

Fast forward to last week, I pull the spark plugs, I notice spark plug 3 is wet with fuel. OK, no big deal, I'll swap the plug and see how she runs. She idled much smoother.

So I figure, plugs are out, let me go ahead and compression test this motor make sure everything is good. This was done cold, with all the plugs out of the motor. Well, basically my worst fear, compression test across the board were as follows:

Cylinder 1: 148
Cylinder 2 148
Cylinder 3: 148
Cylinder 4: 98 and 102 (?????)
Cylinder 5: 148
Cylinder 6: 148

So obviously, cylinder 4 being low compression is not good. I am absolutely baffled at what caused this because I baby the car, hardly redline the damn thing, and drive it basically like a grandpa and only rarely. I started to think it was possibly my injectors when it was missing, which may have caused too much or too little fuel.

But now I am not sure what happened. I guess best case scenario at this point would be an issue with the head, like a bent valve or seal somewhere, but I really have no clue what to expect.

I peaked into the cylinders and found cylinder 3 damp with what seems like fuel, which adds up because the plug was also wet with fuel. Cylinder 4, piston looked dry like the rest. I was not able to get my boroscope to see the cylinder walls, so I'll try that next.

Here's pictures of said cylinders:

Cylinder1:

Cylinder 2:


Cylinder 3: (wet with fuel)


Cylinder 4: cylinder with low compression

Cylinder 5:


Cylinder 6:


I will be doing a leakdown test next, and will update this thread with results.

Creating this thread for any guidance on where to go from here. Any advice or has anyone had a similar situation or symptoms that can help me figure out what is going on or what caused this. Car is tuned by Hassan and has a CSL airbox, running MAP sensor. Euro headers, exhaust, other than that stock motor.

Basically my worst nightmare (anyone with OCD can relate).

[enjoy_m3]

If you're leakdown checks out. I'd start with the injectors, have them tested. If that's really fuel wetting cylinder 3, then the injector might have a slight leak or improper spray. Might as well have them all tested and flow checked. If you're still have the same issue after the injectors are good, then the rings are likely sticking. I haven't seen this happen much on s54s but maybe because most owners do drive the car relatively hard on occasion to redline. I do believe this is common on m54 and I just had a similar issue on my daily wagon with a consistent cyl 4 random misfire (even after fuel and spark tune up).

I ended up buying ac delco x66p and put about 1 oz on each cylinder through the spark plug hole. Let it sit over night, fired it up next morning and let it idle to warm and drove it hard around for about 30 min. It has fixed my issue and the car feels much more responsive from restored compression.

Hope this helps.

[Arith2]

Looks like cylinder 3 has more carbon in it than the other ones and appears damp. What's the firing order?

[BMWahba]

If you're leakdown checks out. I'd start with the injectors, have them tested. If that's really fuel wetting cylinder 3, then the injector might have a slight leak or improper spray. Might as well have them all tested and flow checked. If you're still have the same issue after the injectors are good, then the rings are likely sticking. I haven't seen this happen much on s54s but maybe because most owners do drive the car relatively hard on occasion to redline. I do believe this is common on m54 and I just had a similar issue on my daily wagon with a consistent cyl 4 random misfire (even after fuel and spark tune up).

I ended up buying ac delco x66p and put about 1 oz on each cylinder through the spark plug hole. Let it sit over night, fired it up next morning and let it idle to warm and drove it hard around for about 30 min. It has fixed my issue and the car feels much more responsive from restored compression.

Hope this helps.

When you say rings are sticking, what do you mean exactly? Thanks for the response.

[BMWahba]

Looks like cylinder 3 has more carbon in it than the other ones and appears damp. What's the firing order?

I don't actually think it has more carbon than the rest, I think it just looks way more noticeable because it's wet. The firing order on S54 iirc is 1,5,3,6,2,4

[enjoy_m3]

When you say rings are sticking, what do you mean exactly? Thanks for the response.

I'm not sure if the s54 is exactly the same issue but the m54 has an issue with the rings sticking due to carbon buildup, so it doesn't expand causing misfire or low/loss of compression. The quick fix is the top end cleaner, if it doesn't work then the engine will have to be taken apart. The e46 forums mentioned it and I tried the top end cleaner and it worked (this is after full tune up, new fuel pump, injectors serviced at RC, smoke test for any leaks, etc..). I just didn't do a compression test because it was the last thing to do and I had nothing else to diagnose. No more cold start misfire, or hard warm start after sitting a few hours.

Any luck with the leakdown test?

[sapote]

" I ordered 6 new coils, but before installing them, I drove the car one more time to see if it was still doing it, and it had completely cleared up. Ran beautifully, no misses, no stumbles.
Parked the car, sat for about another month and I decide to drive it again. Well, she ran absolutely horrible. Was misfiring a lot at idle."
Cylinder 1: 148
Cylinder 2 148
Cylinder 3: 148
Cylinder 4: 98 and 102 (?????)
Cylinder 5: 148
Cylinder 6: 148

I wouldn't worry about Blogs low compression, as engine was running perfect one month before. I think low compression was due to wash-down by raw fuel from misfire. Add a spoon of oil in Blogs and run compression again.

[tlow98]

" I ordered 6 new coils, but before installing them, I drove the car one more time to see if it was still doing it, and it had completely cleared up. Ran beautifully, no misses, no stumbles.
Parked the car, sat for about another month and I decide to drive it again. Well, she ran absolutely horrible. Was misfiring a lot at idle."
Cylinder 1: 148
Cylinder 2 148
Cylinder 3: 148
Cylinder 4: 98 and 102 (?????)
Cylinder 5: 148
Cylinder 6: 148

I wouldn't worry about Blogs low compression, as engine was running perfect one month before. I think low compression was due to wash-down by raw fuel from misfire. Add a spoon of oil in Blogs and run compression again.

agree with this. If that cylinder’s oil coating was washed away it wipes out compression.

I wouldn’t overly worry until you’ve tried this oil test.

[Cubieman]

My buddy recently restored compression to a cylinder on a S85 with transmission oil, cylinder had been washed by a leaky injector.

It most definitely can work.

[BMWahba]

" I ordered 6 new coils, but before installing them, I drove the car one more time to see if it was still doing it, and it had completely cleared up. Ran beautifully, no misses, no stumbles.
Parked the car, sat for about another month and I decide to drive it again. Well, she ran absolutely horrible. Was misfiring a lot at idle."
Cylinder 1: 148
Cylinder 2 148
Cylinder 3: 148
Cylinder 4: 98 and 102 (?????)
Cylinder 5: 148
Cylinder 6: 148

I wouldn't worry about Blogs low compression, as engine was running perfect one month before. I think low compression was due to wash-down by raw fuel from misfire. Add a spoon of oil in Blogs and run compression again.

Don’t quite understand though, cylinder 3 is the one wet with fuel, cylinder 4 was normal. My misfire was on 3. Low compression on 4.

So you guys are suggesting add a spoon of engine oil to each cylinder and re-do the compression test? I was under the impression that if I re-do the compression test with oil added to that cylinder and it goes up, that would indicate a bad piston ring. Is this not the case?

I suppose all of this could be traced back to a bad injector I would presume, and perhaps caused by the car sitting with ~6 month old fuel.

[BMWahba]

Also, would you suggest adding the cold oil to a cold motor and do a cold compression test or do this warm?

[tlow98]

Ok, yes, that makes sense what you said. I read that wrong.

it’s definitely still worth trying the oil trick. I’d do it at whatever temp you had the engine before so you an apples to apples comparison.

The caveat is that if you have a failing injector on cylinder 3 I’d get that replaced before starting again. Sadly, they’re like $450 a pop at the dealer now.

but you don’t need to go tempting fate with a leaky injector.

do you have an app to monitor or read your fuel trims?

[BMWahba]

I do not, but can likely swap in a verified good spare injector for the sake of demonstration.

[tlow98]

I do not, but can likely swap in a verified good spare injector for the sake of demonstration.

OBD fusion (app) and a Veepeak reader (OBD dongle) are the easiest to use/install if you want to monitor your trims. They’re a staple over on e46 fanatics.

I might swap in two known good injectors just in case. Cylinders 3 & 4.

this is an odd situation. These motors don’t fail this way, typically. How many times did you compression test number 4 the first time around?

[BMWahba]

OBD fusion (app) and a Veepeak reader (OBD dongle) are the easiest to use/install if you want to monitor your trims. They’re a staple over on e46 fanatics.

I might swap in two known good injectors just in case. Cylinders 3 & 4.

this is an odd situation. These motors don’t fail this way, typically. How many times did you compression test number 4 the first time around?

Hence my extreme frustration, sadness and confusion all at the same time. This car was running perfectly and I don't beat on it. It sat with "oldish" fuel in it, that was the worse thing that happened. And that fuel was about 6 months old, max.

I tested it twice cold, one at 98 and the other at 102.

I am doing the oil spoon method today. Will update.