[dbworld4k]

I had my car protuned once again, this time optimizing for 93 octane. As a preventative measure I changed all my plugs and coils, too, with NGK 1 step colder iridium plugs and Bosch coils in anticipation of freshening up the car before I dyno it on Saturday.

The plugs had 30k EDIT: 20k (I can't maths, lulz) miles on them from August 2014. All but one of the coils were original, so 105K () on them. No serious misfires, but I had noticed a random rough cold start/idle these days, which was another reason why I figured I may as well change out everything.


A few of the plugs were fouled, but cylinder #2 worried me the most. It looked horrid.





Initial thought was the car is running rich, or worst case - bad valve seals but I'm not blowing out any smoke whatsoever. However, I noticed a leaky valve cover gasket and a hairline crack on the calve cover near cylinder 2. This could be seeping bits of oil (though I've never had to top up between 5K oil change intervals, so I'm assuming it's an extremely minor leak) into that chamber, possibly?

I did a data log to check some points:
http://www.datazap.me/u/dbworld4k/pt...ata=1-12-18-22



As you can see, AFR is fine, as is the cyl. 2 timing corrections. Nothing stands out from this log and the car pulls like a freight train. :/

[mr.335i]

Tuned cars should be changing plugs every 25k.

[kaigoss69]

There's about 48 different threads now with people having one or more fouled plugs (including one from me ). Common theme? - Injectors leaking.

[techwhiz]

Originally Posted by mr.335i

Tuned cars should be changing plugs every 25k.

This..... Tuned cars will have random misfires with older plugs.
The more past 25K you are the more likely a miss will occur.
The higher cylinder pressures of a tune cause the flame front to die on older plugs, causing a misfire.

[dbworld4k]

Originally Posted by mr.335i

Tuned cars should be changing plugs every 25k.

You're right. I made a mistake in my subtraction, I changed them at 85K and now it's at 105K (20K miles on them and not 30K, woops).

Originally Posted by kaigoss69

There's about 48 different threads now with people having one or more fouled plugs (including one from me ). Common theme? - Injectors leaking.

Yeah thats a notoriously common failure, but other than a fouled plug, there's nothing else to suggest the injector going bad. After the new coils and plugs, there is absolutely no sputtering on cold start nor idling issues. Seems like whatever minor nuances I was having, it's resolved :/

Originally Posted by techwhiz

This..... Tuned cars will have random misfires with older plugs.
The more past 25K you are the more likely a miss will occur.
The higher cylinder pressures of a tune cause the flame front to die on older plugs, causing a misfire.

Agreed. The plugs had 20K on them, most of them grandpa driving roadtrips.

[derrick603]

Originally Posted by kaigoss69

There's about 48 different threads now with people having one or more fouled plugs (including one from me ). Common theme? - Injectors leaking.

Same here, I had a fouled plug #6. Leaky injector was the culprit.