SwedeSpeed - Volvo Performance Forum banner
1 - 9 of 9 Posts

·
Registered
Joined
·
1,083 Posts
Discussion Starter · #1 ·
Just gapped my spark plugs after having some issues with cylinder 4 misfiring and swapping out coils on that cylinder twice with no change. Had replaced with OEM Volvo plugs about 7k ago but never checked the gaps. Gaps on all plugs were about 0.030-0.031 except cylinder 4 which was around 0.033-ish. Regapped all plugs to excatly 0.028 and it idles sooooo smoothly.

Can this minuscule difference really cause a rough idle and some stutters and very occasional misfire or hesitation or is this just the placebo effect? Anyone else have an experience like this?
 

·
Registered
Joined
·
170 Posts
Just did the same thing, I had a misfire issue and it fixed that and the rough idle. I gap them down to 0.026 which seems to be perfect for my car.
 

·
Registered
Joined
·
181 Posts
Hmmmmm. Interesting. What is the factory gap supposed to be on the Volvo plugs?
 

·
Registered
Joined
·
8,062 Posts
Supposed to be 28 thou, but as you have learned several more is all it takes for the coil to start having issues jumping a spark. Bigger gaps mean higher voltages which can jump somewhere inside the coil windings instead of the plug.
 

·
Registered
Joined
·
1,083 Posts
Discussion Starter · #5 ·
Just did the same thing, I had a misfire issue and it fixed that and the rough idle. I gap them down to 0.026 which seems to be perfect for my car.
I'll have to try that next time I do plugs.

It's pretty crazy how a couple hundredths of an inch can throw things off so much.
 

·
Registered
Joined
·
4 Posts
.28 to .31 requires exponentially more energy to jump the gap, not just 10% more energy. I'm going to install some new plugs with .28 over the weekend. BTW -- be VERY careful to NOT touch the iridium post on those plugs when gapping them. The post fusing will weaken and then you have a diamond hard metal piece bouncing around in your cylinder, scoring walls or valve seat(s). I was lucky and the iridium post broke off while I was adjusting -- so I returned the set and went a different route. Personally I wouldnt touch the gap on an iridium - just spec it in the store very slowly and carefully with undersized feeler gauges to see if you want it.
 

·
Registered
Joined
·
1,083 Posts
Discussion Starter · #7 · (Edited)
Oh ****! I was pretty careful but my the gauge did touch the tips on all five. Not very hard, I was definitely gentle with them so hopefully I'm good. I used to have a 150cc moped that the tip of the spark plugbroke off inside the cylinder and ruined the engine so I don't wanna go through that again. Maybe I should just buy new plugs lol.

How are you supposed to check the gap on iridium plugs then?
 

·
Registered
Joined
·
8,062 Posts
Just check them carefully, you don't want to be putting force on the irridium part of the electrode. Its not that fragile if it can handle a bunch of fuel explosions in the cylinder, then again it not something that was designed to have you prying on it either.

I use one of the circular gap checkers on mine, but very gently.
 

·
Registered
Joined
·
1,083 Posts
Discussion Starter · #9 ·
Sweet same here, I feel like I was pretty gentle with it. Hopefully I won't have one break off in the cylinder lol.
 
1 - 9 of 9 Posts
Top