So I posted about the fuel consumption & stalling after a cold/warm start issue I was having with my 2012 m56x with 56,000 miles. I didn't want to post in that thread as it got convoluted with a bunch of posts of me trying to pinpoint the issue.

I changed my plugs about less than 150 miles ago and only drove the car a handful of the times. I was still having the issues. Cleaned my MAFs, still the same issues with a bunch of permanently stored MAF codes because I pulled the harness out to clear my fuel trims.

Anyhow, the car was running super rough and I did get a misfire code in in cylinder 8. I cleared it and it never came back. I decided to check the plug today to see if it was torqued correctly and it's overall condition...it was torqued, maybe could have been a bit tighter.

This is what it looks like (top plug) after less than 150 miles. There is oil along the sides of the plugs. The bottom two are the older original plugs from cylinder 7 & 8 - these both also had a lot of oil all along the threads .




What would cause this? Improper torque or something more involved

For what it's worth, the rest of the plugs only had oil at the tip of the plug. All had a lot of carbon build up.

Now I'm not 100% sure if they were the original plugs, but I'm thinking that if someone changed them out, perhaps because the back two plugs are so hard to access, maybe they didn't torque them 100%?

Shanehsmp wrote: ↑

Tue Feb 23, 2021 1:10 pm

but I'm thinking that if someone changed them out, perhaps because the back two plugs are so hard to access, maybe they didn't torque them 100%?

Certainly possible, but you should also consider valve cover gasket leak, do you have evidence of any oil leaking elsewhere?

pedsemdoc wrote: ↑

Tue Feb 23, 2021 1:47 pm

Certainly possible, but you should also consider valve cover gasket leak, do you have evidence of any oil leaking elsewhere?

I thought so as well, but the side of the gasket/cover is dry, the spark plug cylinder and boot are both dry as well.

pedsemdoc wrote: ↑

Tue Feb 23, 2021 1:47 pm

Certainly possible, but you should also consider valve cover gasket leak, do you have evidence of any oil leaking elsewhere?

Maybe the smaller plug gasket itself could be bad/unseated? It's just funny that it's only the two rear ones. Going to go reinstall and check the plug and re-torque cylinder 7 as well.

Figure I'd follow this thread up for anyone with similar issues.

I took all my plugs back out after noticing that the original plugs all had smaller than 0.040" gaps. Low and behold, all of the new plugs were all lower than 0.040" as well. Did a Google search and found that this might be caused by low octane gas/poor combustion in the chamber. I re-gapped all the plugs, got some better 91 from a busy gas station (the one I've been using likely doesn't see much traffic for 91 octane) and did a walnut blast/carbon clean - I've been driving the car all week with no issues. My gas mileage has returned back to a decent combined rate of about 15.4 mpg....it was at 12mpg or lower since mid October.

I'm still showing a bit of a misfire in cylinder 7, going to check that again soon, but for now I'm happy that the car is running good. I do fear that I have done some damage to my cats and Evap system somehow as I still get a gas smell from the rear on a cold start. I'll have to check the Evap canister for any issues as well.

Thanks for the update. I am glad your car is back to running reasonably well, and that your goal of increased/regained fuel economy is achieved.

***
While I don't have any answers to the other symptoms you have expressed, I figured this would be a good opportunity to get on the soapbox.
This is a general statement on the Evap system, that I am making indirectly for the benefit of the masses who might stumble upon this thread.

For those that didn't know, you are not supposed to "top off" your gas tank when refuelling. Whenever the pump clicks, leave it alone.
If not, I can guarantee you will be dealing with Evap system issues down the line. Well, you or the poor schmuck that buys the car.