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With my never ending saga of reduced ECU performance due to some sort of knocking, I decided to try a colder plug last weekend on the suggestion of another Revtronix user. Bought NBK BKR7E plugs and gapped them to ~0.35mm. Immediately after the car started, I could tell the engine was missing/misfiring occasionally. For example, holding at 2000 rpm, one can some times watch the rpm gauge bounce down. While coasting in gear, more noticeable 'bucking' and overall a rougher idle. Obviously I need to either change back to the BKR6E's or do something else to these...

Did just changing the spark plug colder result in the engine missing now or did plug wire(s) just go bad?

It could....but I'd definitely suggest checking the ignition system wiring and such.

As an aside....I'm going to get on my soap box about colder plugs. I think this is one of those old school hot rodding type things that have carried forward and in my opinion on about 90% of the setups out there is complete unecessary.

Back in the day hot rodders may have used colder plugs to extend the plug life when running much higher compression ratios. If they didn't the electrode would get burnt up due to the plugs getting and staying too hot, and as a secondary result of the plugs staying to hot, the engines may have problems with pre-ignition.

It is true that turbo cars increase compression ratio and all that, BUT plug design has drastically improved, AND unless you are seeing burnt electrodes or signs of pre-ignition, I can't see any reason to go with a colder plug.

That's my take on the colder plug thing. There are probably some more opinions and thoughts on the matter, and by all means feel free to share. I will say that I've 20 psi of boost on stock plugs and they show no signs of burnt electrodes or other issues.

Agreed, as my TW ran just fine with this same setup on stock plugs + stock gapping. I'm near my wits end though, short of disabling the knock sensor, to troubleshoot my performance problems on this body+engine though, so game for trying things. Although, there are plenty of other forums for turbo cars which state that a colder plug for non-oem setups are the way to go.... my plugs are just sooty, but that's expected for my limping ECU atm.

What gapping are you running at? oh yea, seems like a dumb question, but whats the proper way of gapping plugs? I've always just bent down the tip of the plug and then measure/adjusted with the feeler gauge to the correct spacing. Should the whole tip of the plug be level instead of angled down?

I would try the stock heat range plugs with a tighter gap before moving colder.


I ran the 7's at .028", but it may have been overkill. The COP setup may negate the need for that.

Thank you Josh for clarifying this for me. I thought it might be old school thinking. VERY helpful to have one less detail to think about. The revtronix guy was recommending but his background was foxbody stangs so I think we're talking 80's here.

The colder plugs will just be more likely to foul. In the old days, many of those hotrods running on the colder plugs weren't really meant for traffic driving, especially with the poor fuel management of the day. I agree with trying to reduce the gap a little.

i ran colder plugs in my STi. but u need a tune if ur going to run them. ive had a few 70s and 80s muscle cars, but back then u messed with a carb, not a computer when running colder plugs.

Pulled out the BKR7E plugs this afternoon, as I've had enough of the misfiring crap. Looks like they were overheating (pics to come later) as the tips were flaking with yellow/white stuff, while the ring/base was black/sooty. Measured the plug wires and all are around 5K ohm, so still good.

Reinstalled the BKR6E plugs and gapped to ~0.31mm. Did some highway driving and it's much better/smoother than before. Although, while driving slow in the city, if the RPMs are under 2000, then the engine does a lot of jerking. Why's that caused by the smaller gap?

I'd be curious to see the pictures. How do they compare to these?

http://www.main.experiencetherave.com/s ... /ngkplugs2
http://www.main.experiencetherave.com/s ... /ngkplugs3

I had already put them away into their containers, so more of that yellow/white stuff on the tip has flaked off, but you get the basic idea...

So the yellow/white stuff flakes off to reveal the black sooty electrode?

The yellow/white stuff is only on the top of the plug. The base/threads are always sooty.

At least according to Q: How do I "read" a spark plug? and the following image, I came to the conclusion that the plug was overheating.


Anyways, having the BKR6E gapped at 0.31mm is much too small for daily driving. Too damn annoying all the jerking while lightly applying throttle/coasting. Need to regap to 0.38 or so tomorrow.

Since I'm the 'guilty party' that BSOD mentions in his OP, I thought I'd speak up. I've had a similar issue w/the Revtronix chip where the Spark Learn Factor/Octane Factor (OF) drops from an optimum of 90-100%, to 50% or less (0 in BSOD's case) due to the ECU seeing knock.

I read online that over 1.2 BAR/17.2 psi, a step-colder plug was recommended (this was may well have been based on ol' school experience as Josh described). As I'm running 17-18.5 PSI w/the TD05 (16-17 w/the TD04) I thought I'd give the colder plugs a try - I gapped them to .030.

I thought they were helping my OF as it stayed up for a couple tanks of fuel, but started dropping this last weekend, which included much colder temps (15-20 degrees cooler) than the previous week when it was looking good...not sure if there's a correlation or not.

My car seems to run the same w/the colder plugs - starts/idles/cruises/boosts- the same. I hooked up my WB over the weekend and it was running @ 11.5 @ full load/throttle when I still had the TD05 installed.

I've got to swap out the 90 elbow into the TD04 tomorrow, so I'll look @ the plugs too.

I'll just throw this out there in left field.....but I've read too many random odd posts where people are fighting odd issues with the Revtronix chip. It may be a great little chip, but I think sometimes with whatever changes are made, the ECU is fighting itself.....

The chip was designed to be able to learn to some degree. I think the main thing is timing is changed slightly, bcs program is setup to be more gradual and for higher psi, and injectors are scaled properly to whatever you are running.

Now regarding what is creating issues? Who knows there are so many variations from car to car and I think alot of this has to do with our intake systems and wiring of the car degrading. It would have been great if revtronix gave us a way of tuning the ecu because I believe every car will need to be tuned differently, like if valve springs aren't holding higher boost properly or something similar.

What I have found is the 2 BPV I have do leak air, and it sounds like many people are just trying different bpv's but they are all old and used with worn rubber and spring.

Well the ECU is trying to compensate (somehow) for the smaller gap size by having the idle crazy high while cold. This morning, at stop lights the RPM was staying at 3K or 4K and would eventually SLOWLY go down over the course of ~60 seconds. I've gotta find the time to re-gap these things back to their normal range...

<<<What I have found is the 2 BPV I have do leak air, and it sounds like many people are just trying different bpv's but they are all old and used with worn rubber and spring.>>>

Giving away secrets here...

http://www.forgemotorsport.com/content. ... =FMDVMSP02

BSOD2600 wrote:Well the ECU is trying to compensate (somehow) for the smaller gap size by having the idle crazy high while cold. This morning, at stop lights the RPM was staying at 3K or 4K and would eventually SLOWLY go down over the course of ~60 seconds. I've gotta find the time to re-gap these things back to their normal range...

Plug gap should not affect a high idle like that.....

Adam: So you're suggesting that my BPV just started to go out this week 'eh? It still holds boost ... well the measly ~10 PSI I'm limiting myself too.

Josh: I'd agree, but I haven't changed anything else these past 2 weeks besides plugs/gaps. Unless something else just decided to break/go out this week and totally unrelated.

Anywho, soon as I get home tonight, gap goes back to ~0.38mm. Then will see if I have another old BPV sitting around from the swap. If not and the ECU doesn't re-adjust things after a day or two regarding the idling... then I suppose time to buy a new BPV.

I'm an idiot.

Soon as I got home, I changed and quickly took out the first spark plug. Re-gapped it to 0.38 and put it back in. Took out the next plug and gapped it to 0.38.... then started to recall that this gap was still seeming way too small from OEM. Hmm, wtf?

This last time I bought spark plugs, I decided to not use the crappy 'disk' gapper and instead bought this fancy set of Craftsman gapping gauges from Sears. While I knew that gapping for our plugs, people were ranging from 0.44 to 0.30, the part I failed to pay attention to was the measurement scale.

The past 2 weeks I've had my plugs gapped to 0.35 and 0.30 millimeters instead of inches! 0.356mm = 0.014 inch and 0.305mm = 0.012 inch -- oops!

Now the BKR6E-11 are gapped back to 0.035 inches. I'll give things another few days to see how the ECU compensates.

Either way BSOD if your running the original bpv replace it. I have 2 here that leak. I have opened one of them up and the rubber seal is a piece of hard plastic + when the heat in the engine bay makes the spring hot, it probably has even less tension.

I can get the oem one for $100. I am sure the oem just does as well of a job as the aftermarket just oem is cheaper.