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Plug Gapping and Misfiring

adam 32

By adam 32,
in Engines & Forced Induction

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adam 32 Grand Master

adam 32

Posted
Posted

i was gettin a misfire on high boost before, so i put in new plugs gapped to 0.76mm (damn non-metric feeler guages:D )

anyway, now it pulls hard all the way to redline on 1bar boost, but it seems to misfire at idle?! (sounds like ive got cams!) is this because im now running too small a gap? or is this what you sacrifice in order to get a reliable spark under high boost?

thanks

adam

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rev210 Grand Master

rev210

Posted
Posted

Could be the smaller gap and worse still if you have installed a colder heat range of plug.

The smaller gap/colder plug provides better combustion for top end (as per the reason you did it) but, provides poor combustion at idle. The plugs will have less life in them as well.

Best thing to do is practise changing plugs, so you can change to a colder set for race use and leave a nice warm setting for the street. Poor combustion also shortens the life of the engine BTW.

adam 32 Grand Master

adam 32

Posted
  • Author
Posted

but theres only poor combustion @ idle so should be sweet:P

i dont fancy changing plugs THAT often, took me long enoug thanks to nissan's coil packs :) the plug is 1 heat range colder, so thats gunah add to it as well.

i guess im sacrificing the bottom end for top end, as it seems to go with turbo cars when they make big power.

rev210 Grand Master

rev210

Posted
Posted

The plugs foul at idle, and get cleaned up when you floor it.

They just won't last as long as your old ones. Why not run the gap at 0.9 or so, with a colder range plug I'm sure you won't be down any power and it will give back the idle perhaps.

Zahos Mentor

Zahos

Posted
Posted
0.9 on a colder plug should be fine.

Nope! I've tried numerous combinations with heat range and gap, and what I'd recomend for street use is a heat rating of 6, and a gap smaller than 0.8mm. If you have an aftermarket ECU, or a SAFC, then this recomendation doesn't really apply to you...

With stock ECU, b/c the mixtures can get really rich, you need a warmer plug that can burn some of the carbon deposits off the plug. The colder plug will not last long, as it will get fouled very quickly (a couple of weeks), and will need to be pulled out to be cleaned. A warmer plug will go a lot longer before it needs a clean.

As for gap, I've tried

0.9 with a colder (7) plug, 0.8 and 0.7 as well. I found the smaller gap to be the best....

But like I initially said, a warmer plug and smaller gap is best for street use..

I'd say NGK BCPR6E (NO S). This has a heat rating of 6, and the v groove. Gap this anywhere between 0.65 and 0.75, and your Line will run much better (remember, only if you nave stock ECU meaning rich mixtures). At this configuration the 5000rpm misfire on the R33 happens much less!

I only see it when I have been driving the car for more than 30 mins... weird!

Zahos

JH32 Grand Master

JH32

Posted
Posted
Originally posted by Zahos

But like I initially said, a warmer plug and smaller gap is best for street use..

I'd say NGK BCPR6E (NO S). This has a heat rating of 6, and the v groove. Gap this anywhere between 0.65 and 0.75, and your Line will run much better (remember, only if you nave stock ECU meaning rich mixtures).Zahos

Zahos ... does this apply to R32s as well??

Zahos Mentor

Zahos

Posted
Posted

OK then, well I guess the same theory applies to R32's as well. But no matter what, if u have stock management, and higher boost, you will see this problem. What I suggested merely deminishes the magnitude of the problem, and will prolong it from creeping up. I have had my plugs in for 2 months now, and I dont see the problem very often (running 0.7 bar ~10psi).

rev210 Grand Master

rev210

Posted
Posted
Originally posted by Zahos

Nope! I've tried numerous combinations with heat range and gap, and what I'd recomend for street use is a heat rating of 6, and a gap smaller than 0.8mm. If you have an aftermarket ECU, or a SAFC, then this recomendation doesn't really apply to you...

As for gap, I've tried

0.9 with a colder (7) plug, 0.8 and 0.7 as well. I found the smaller gap to be the best....

But like I initially said, a warmer plug and smaller gap is best for street use..

I'd say NGK BCPR6E (NO S). This has a heat rating of 6, and the v groove. Gap this anywhere between 0.65 and 0.75, and your Line will run much better (remember, only if you nave stock ECU meaning rich mixtures). At this configuration the 5000rpm misfire on the R33 happens much less!

I only see it when I have been driving the car for more than 30 mins... weird!

Zahos

Adam's got an HKS AFC thingo.

Like you I run the stock rated 'warm' plug. Regardless of gap they (warm plugs) will have a nicely cooked electrode in no time with a setup like Adams with revs and tO4 style boost.

adam 32 Grand Master

adam 32

Posted
  • Author
Posted

the problem doesnt seem to be as bad anymore actually. im not sure why...

even if it didnt rectify itself i was happy to run a 0.75mm plug gap as it pulls very nicely through top end

jimi if ur running the VG30 at that sorta boost (which u should :D) then run the same plugs as me. i think theyre BKPR6ES or something

Black33 Proficient

Black33

Posted
Posted

what gap do u guys think I should run:

I have -

full exhaust (dump, front and rear)

10 - 11psi boost

pod

cold air intake

Also, how long does it take to remove all of the stuff under the plastic panel on the engine head to get to the plugs? is it hard (i got to it and then stopped)?

thanks

Zahos Mentor

Zahos

Posted
Posted

Try 0.7 or even 0.65+

A good spark plug (copper) is NGK BCPR6E

Platimuns r good, but not worth the money, as the only benefit they have is a longer life span. I dont plan to leave plugs in there that long anyhow, as they foul easy when running rich....

R32 Zilla Community Regular

R32 Zilla

Posted
Posted

I have the same problem with my r32

Running 19 psi through a hks gt2535 and a rechipped computer it misses at about 5000 rpm.

Have tried lots of different things to fix it with no luck yet.

Iam now running a gap of .65 and when i did this it developed a miss at idle (like adam32) . This does not worry me as all i want is for it to rev cleanly to redline.

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