[SOLVED] Cylinder 1 Misfire - P0301 / P0300 Mystery

[Toothbrush]

149600 miles

[ard]

Originally Posted by Toothbrush

Since it's too cold to do anything, been trying to learn more about fuel trims and 02 sensor data. As I (currently) understand it, since sensor 1 & 2 are wideband, then 0.0 mA = stoichiometric. Positive number means going lean, negative means going rich.

Looking at the numbers from a Carly Gen2 adapter + OBD Fusion (pro), looks like Bank 1 is much leaner than Bank 2. I measured 900 pts (changes in reported values) and compared them, along with RMP and saw the following:

Average Bank 1 - .505mA
Average Bank 2 - .163mA

Average difference between the two over that time = 434%

This appears to be more evidence of unmetered air/vacuum leak... ? Sprayed Carb cleaner around Cylinder 1 fuel injector and intake while watching RPMs, didn't notice any changes.

I really thought this would point you at the issue....

Can you run a Vanos Function test??

[Toothbrush]

Not exactly sure...

Went through ISTA to see what I could find. This was the closest I came. Let me know if I should be looking for something else/more specific.

[pshovest]

A VANOS problem should affect all cylinders in the bank, not just 1.

[ard]

1. I dont think that is a vanos function test. Just the status. INPA has one, at least for my M62

The vanos function should try to position the vanos at the extremes...if it cant, thsi MAY cause the engine to run very rich or lean in certain RPM bands.

2. I am not convinced this is a singular "only cyl 1" issue. OP reported cyl misfire AND 'random' misfires.

[Toothbrush]

While trying to figure this out noticed a coolant leak and spent quite a bit of time trying to track it down. Thought maybe the valley pan based on others posts, but couldn't quite tell until I used some UV dye - made it shine bright...

Would a bad valley pan gasket cause a misfire on a specific cylinder or just account for the random misfire code (P0300)?

[Toothbrush]

Update: Have the intake off now, break for lunch, then will get back to getting the valley pan gasket off.

However, wanted to see what people thought about the condition of the intake valves...

Does it look like the intake seal has failed and this could be the source of the misfire? There's a good bit of buildup on cylinder 1 of oil (?) and some of the rest have a similar, but less sever buildup. Also, the first nut on Bank 1 was not as snug as the rest.

I could never get smoke to show there or get the idle to change with any type of spray.

In case you're wondering, coolant looks green due to the UV dye as I do use BMW blue.

[Skyline]

Clearly the valley pan needed to be done; if not the coolant transfer pipe as well. Probably unrelated to your issues though.

That oil build up is pretty significant. Have you ever done the valve guide seals? You're a bit beyond the normal mileage for that, so it's likely an issue. I'd be surprised if you were not seeing the significant symptoms of that: Idle for a few minutes then hit the gas and see a large cloud of white smoke out the exhaust.

If you decide to do the seals, I have an AGA kit for rental in the "For Sale Section". PM me for info.

[Toothbrush]

Yep, I've done the whole smoke screen deal and got a t-shirt

Replaced the valve stem seals last part of 2017 before it got cold. Had the misfire ever since.

The first nut on the Intake (bank 1 side - front corner) was not torqued down properly when I started pulling it apart, so I'm hoping maybe, just maybe whilst laying across the engine a few times to do the valve seals that particular nut loosened up enough to cause a vacuum leak I couldn't see (even with smoke) and caused this whole mess.

I used the AGA set and a lot of patience!

Currently in the middle of cleaning up the intake and ports as carefully as possible... (new BMW valley pan gasket in place)

[Skyline]

Originally Posted by Toothbrush

Yep, I've done the whole smoke screen deal and got a t-shirt

Replaced the valve stem seals last part of 2017 before it got cold. Had the misfire ever since.

Well, the plot thickens! So if the misfire started right after you did the valve seal job, that tells us something. Either something you did wrong caused the misfire, or it was just a coincidence. As for me, I'm not a big believer in coincidences.

For starters, I'd look all the way around the valve covers very carefully for any signs of an oil leak. You'll need a mirror for the back ends. I'd also pull all the coilpacks and shine a light into the tubes to see if any oil is in there.