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

[tlow98]

No leakdown.

Hot compression test results after idling the car, all cylinders reading 150 psi.

so…..yeah….

well, that’s great.

im not entirely sure what the next move in this situation it. Strange

[BMWahba]

No leakdown.

Hot compression test results after idling the car, all cylinders reading 150 psi.

so…..yeah….

[enjoy_m3]

Did you do a leakdown? Would verify the rings aren't sealing if there is no leaks on the valves.

[BMWahba]

Yea definitely makes not much sense. I am going to swap plugs today, put it all back together and idle it. Then do a warm compression. The boroscope is how I got those picture of the pistons but I wasn’t able to look in the walls. The camera didn’t really fit to turn it towards the walls or it was too shiny.

[tlow98]

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.

Yeah, it’s very surprising. I’m leaning toward the fact that it’s just something simple. Bad gas seems like a stretch.

You snag a borescope?

Do a leak down and see where all that “lost” compression is going.

on my engine that had a blown HG it was very easy to feel/hear the air moving into adjacent cylinders and out through the block with my worn rings. Cylinder walls looked perfect, however.

[BMWahba]

Another question: is there any validity to a possible coil pack failure on one or more cylinder to cause injectors to keep firing and thus cause some of these strange symptoms?

[BMWahba]

Update:
spoon full of oil got compression on cylinder 4 back up to 150.

so please, can someone help me understand what is going on. This is so strange.

Again for clarity: Cylinder 3 is the one that I would suspect a “wash out” considering it was visibly wet. But cylinder 4 is the one I had a low compression on. After adding oil, on a cold compression, all cylinders are reading 150.

How can I rule out a piston ring issue at this stage?

for safety, I am swapping all 6 injectors with a used spare set.

[sapote]

Ha, that's what I thought but here we are..

Fuel is a very good solvent, new or old. You're thinking it's like thick paint. How do you know the leaking injectors are due to 6 month fuel and not something else?

[BMWahba]

“It sat with "oldish" fuel in it, that was the worse thing that happened. And that fuel was about 6 months old, max.”

A year old fuel is nothing to worry about.

Ha, that's what I thought but here we are..

[sapote]

“It sat with "oldish" fuel in it, that was the worse thing that happened. And that fuel was about 6 months old, max.”

A year old fuel is nothing to worry about.

[Tbonem3]

and I don't beat on it

Think I found the problem. Just j/k, sorry you're having issues Michael.

[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.

[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]

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

[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?