Spark Plug keeps loosening up! #6 near firewall

[e30vert]

M20B25
Engine runs great!
Check Engine Light came on and I
heard a light popping sound in engine bay
Traced the sound and determined that the #6 spark plug (nearest the firewall) had worked itself out of the cylinder head and was still attached to the spark plug wire and firing. This cause the popping and slight aeration of fuel smell.

Screwed the spark plug back in to the cylinder head and it appeared to have resistance and tourque down. Drove 250 miles from my Nevada house to the Bay Area. Same issue again. Spark plug is loosened up and making the popping noise again.

Any ideas why this is happening and steps to take to resolve this issue?

[bmwm42]

loctight will fix it

[e30vert]

OK I will try using Blue Loctite and tourquing to 15 -22 ft lbs of torque and see how it does.

[z122643]

Loctite on a spark plug would be my last resort. Is the plug dry or did you apply a little anti seize? Torque spec is 21 ft lbs

[Adrian_Visser]

My bet is the threads are stripped. Heli-coil here you come.

[e46s54dr]

My bet is the threads are stripped. Heli-coil here you come.

Plus 1 on that... There really isn't any other explanation for this scenario other than the dreaded stripped threads.

[b*saint]

Blue loctite is cheaper than a 80 dollar helicoil kit and the labor to put it in.

[Ceeker]

Blue loctite is cheaper than a 80 dollar helicoil kit and the labor to put it in.

you don't use locktite on spark plug threads. the threads on the head are most likely stripped as mentioned. but I suppose for a quick fix it would work. the helicoil is the correct measure to take. I have never done one on a the car; but just to be safe you most likely need to remove the head to avoid any debris going into the chamber. and it is a tight fit to get too. As for anti seize, have used it on the threads and never had problems with plugs backing out.

If you can get to the plug port and are successful in installing the helicoil; blow out the debris with compressed air from the chamber.
you might get lucky.

[reelizmpro]

In my college days one of the spark plug holes were stripped pretty bad on my old 88 325iS. So much so that the plug would literally pop out of the engine sometimes while on the freeway lol. I would JB weld that shit back in just to get by until I found another head and it worked for a few weeks at a time too. The car had over 200+k miles on it so I picked up a rebuilt head and threw it on. That's why I didn't bother with the heli-coil.

[AndrewBird]

You might try a new spark plug first. The crush washer that acts to hold the plug from unscrewing might be worn out from being tightened down too many times.

Use a flashlight and take a look at the hole in the head. Should be pretty obvious if it is stripped.

[e30vert]

Great advise all around. I am hoping against the stripped threads. I got the plug tourqued down before the 250 mile drive and did not want to ramp on it too hard when tourquing so that I did not strip it out. I will try the new plug first as its less expensive and less time consuming AND tourque it to 21 ft lbs of pressure.

Where can the proper helicoil kit be purchased?

If the plug hole threads are indeed stripped then it would be a good time for me to install the ported and polished head that I have on my shelf, but that will be time consuming.

Should I put in a cam while I am at it? Which one? More of a headache than its worth?

If I am forced to go that route where would be the best area of the forum to ask for pointers? This one?



- Update - Just installed a new spark plug in the #6 position and drizzled just a small amount of BLUE (Serviceable) loctite on the lower portion of the threads. Inspected the hole with a flashlight and from what I can determine there are threads still within the hole. I checked the old spark plug for any metal shavings within the threads and did not find any metal particles of any magnitude. Spark Plug gave good resistance when I leaned on the ratchet so it "seems" as if there are threads that the plug can bite into. I checked all the other plugs and did not find any others that were loose.

I used the loctite cause I figure if I am going to need to swap cylinder heads anyway it does not make any difference if one plug (#6) has a bit of loctite on it. Since its breakable loctite then it should allow me to remove the plug at some later date as well.

[Kershaw]

helicoil kits can be bought at autozone.

[Huff]

You might try a new spark plug first. The crush washer that acts to hold the plug from unscrewing might be worn out from being tightened down too many times.

Use a flashlight and take a look at the hole in the head. Should be pretty obvious if it is stripped.

Man, I would try a new spark plug first before ANYTHING else. That crush washer can look okay, but could be the culprit.

[b*saint]

People don't give any supportive evidence as why you would not use blue or even pink loctite on a spark plug. The only thing I can think of is because of the expansion of the head under operating temperature, the loctite would basically not work.

[e30vert]

So far with the new Spark Plug and the small amount of Blue Loctite it has not loosened up again. I still get a check engine light that comes on after the car warms up though. I pulled the spark plug boot and checked for wiggle and the ability to hand turn the spark plug and it wont budge.

I tried the "stomp" test to try and determine the error code , but the check engine light just stays on and does not flash any codes.

Car build date 12/87 - e30 vert with M20B25 engine.
I am unsure if I have the 153 or 173 ECU.
I have added a performance chip and I am wondering if that disabled the stop testability?


3 Questions:

1.How do I determine what ECU I have? Its labeled right on it correct?

2.If it turns out that I have the 153 and want to upgrade to the more robust 173 ECU is it just a matter of finding a good working 173 ECU and installing in place of the 153?

3. Does anyone have a Code Reader that they can lend so I can pull the codes? I can leave a deposit and provide all my pertinent information. Or if someone is local to the Bay Area , Ca then I could travel to meet up.