[mizzourob]

Long time reader, first time posting!

I recently changed the spark plugs and wires on my 2008 Saab 9-7X as I rolled over to 103,XXX miles and was trying to stay up-to-date with service. In the process of changing the plugs, my #2 plug (passenger side front) threads got messed up due to trying to access the plug (from the wheel well). I was able to get the plug back in and drive it a bit. Driving it like this caused constant misfires on cylinder #2 when accelerating. Since this is my daily driver I got a bit scared of reaming/tapping the hole to avoid cross-threading so I took it to a shop to have them look at it. In getting the new plug installed I'm worried that I may have caused the problem by attempting to insert the new plug slightly off-axis.

The shop's machinist was able to clean out the threads and got the new plug further in than I was able to get the plug. It is not all the way in (short by about 1-2 threads), but it holds torque and runs fine at speed. However, at idle it runs rough (particularly on a cold start)and throws a P0302 misfire code if left to idle too long (3+ minutes) without moving. When the engine is above about 600RPM it seems to also run fine. When left to idle (about 500+/- RPM) I can hear a slight hissing sound with the hood open.

I am thinking that it could be a vacuum leak coming from around the spark plug threads. Would this be possible? I was thinking about trying the Permatex black gasket maker cream on the upper plug threads but I cannot seem to find anyone having either had this problem or attempting my fix. Any thoughts?

Thank you to everyone who has contributed so much to this forum over the years! This is the first time I have not been able to find an answer already posted.

 

[AWD V8]

Sorry to hear this.

A spark plug MUST be seated in order for it to cool properly. The plug transfers heat through the seating to the head to prevent the spark plug from overheating. It is possible that the spark plug electrode cold overheat and cause pre-igntion and damage the piston.

You need to take it to a shop to have an insert installed. A skilled tech can do this in most cases without pulling the head, and be successful in most attempts.

Yes the compression will leak around the threads. If you continue to drive it like this it will burn the head material away and the plug will blow out and the head will then have to be pulled to replace it.

 

[mizzourob]

Thank you for the feedback; if only I had the $1400 plus that I was quoted to have someone pull the head. It seems pretty intense from what I can tell. The real issue is that the plug for cylinder #2 is almost squarely behind the front passenger side wheel strut tower in the wheel well. There is seemingly no way to get a drill properly aligned to install an insert without pulling the head completely (which also contributed to it getting messed up in the first place).

Are there any other gasket type sealants that would both stop a vacuum leak and be able to transfer the heat from the plug into the head? Perhaps the Permatex 80697 Copper Spray-A-Gasket Hi-Temp, I would obviously have to be careful spraying it, or is all this really just wishful thinking?

 

[AWD V8]

No sealant should be used. If it sets up hard you will never get the plug out again!
The plug seat needs to physically be seated against the head to transfer heat.

Years ago I've retapped plug hole threads and installed an insert to repair the plug threads without removing the head. It can be done in most cases if the tech knows what he's doing. It should be possible to do it an an hour or so.

Several tools available to do this job.

I think this one is the best.
https://www.youtube.com/watch?v=g3oLj2AOzXw

This guy does one as well.
https://www.youtube.com/watch?v=c_t2mz2tN3w

Things you must know if you do the job that they do not tell you.

MAKE SURE THE PISTON IS DOWN!!!!!!

Also try to ensure the valves are closed so that the tool does not hit the open valves. So you begin at TDC firing and rotate about a 1/4 turn clockwise.

 

[mizzourob]

AWDV8.... you're awesome and thanks for the feedback! :thx I think I'll skip on trying a liquid/gel sealant. I was digging around my engine block tonight and have a couple of new questions, but I'll use a new thread for that to keep topics organized.