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Misfire only under boost?

maximajim
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maximajim Community Regular

maximajim

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I've been trying to correct this problem for some time. Previously it would misfire when cold and high rpm, but i've since changed the head gasket and used ARP studs.

When i did that I left a coupling loose creating a boost leak. When it had the leak, the Engine would rev to redline fine, just without boost. I've since corected that problem too. Now it misfires @~10psi.

I have taped coils, gapped NGK coppers heat range 7 down to 0.5mm.

Could the problem be not enough ignition advance? A/F are about ~11.2:1 and lower. Should I lean it abit?

TIA.

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NZM.031 Grand Master

NZM.031

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if its too far advanced it will ping its head off, if its too retarded it will missfire and run like shit. taped up coils dont stop them from arcing out, id be looking at these and getting a set of splitfires... 11.2 isnt too bad, for the plugs to ignite that much fuel, the coilpacks will be under alot of load to produce such a spark....they then build up so much power, that it finds its way out to the head, instead of to the plug. this could also be why the a/f is really rich.

cheers

Linton

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SLY33 Mentor

SLY33

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taping the coils can help if its a fine crack in the housing, but you may have a dying coil on its way out. As mentioned check out your timing, if its ok, its a plug or a coil issue. But seeing as your running a small plug gap already id still suspect the coils. I had the same problem, gapped down my plugs and it went away. Then it came back later on, that time i taped the coils to fix the problem. Then it came back again as i modded for more power, at which time i upgraded to splitfires and havent seen the problem since.

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maximajim Community Regular

maximajim

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if its too far advanced it will ping its head off, if its too retarded it will missfire and run like shit. taped up coils dont stop them from arcing out, id be looking at these and getting a set of splitfires... 11.2 isnt too bad, for the plugs to ignite that much fuel, the coilpacks will be under alot of load to produce such a spark....they then build up so much power, that it finds its way out to the head, instead of to the plug. this could also be why the a/f is really rich.

cheers

Linton

It rev's fine without boost and high rpm. I can't see why the coil would work then and not under boost. Am i wrong here?

As for replacement i'm looking to buy GM LS2 coils, they are ignitor on coil like S2 rb25's and a much cheaper.

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mad34 Experienced

mad34

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i have the same problem and its driving me crazy . i have a tiptronic r34gtt. The miss is only under boost and to top it off it doesn't happen all the time. i am running iridiums gapped to 0.6 it only happens every now and then aghhhhhh :) ...mostly when the engine is hot, but sometimes when it is cold.

someone said something about the std ecu making it richer when it is boosting more than std and that makes it miss??

i checked my coils and they looked brand new even smelt like new plastic. seeing as it works most of the time i dont think it is them because usually coils are either stuffed or working there isn't really an in between. What i might try is cleaning my coils thouroughly then coating the inside of the rubber boot with dielectric grease. That is the only thing i can think of.

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boost33 Contributor

boost33

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I had a similar problem, misfire under boost

Checked idrium spark plugs, they looked mint, checked the gap and all

I even changed the fuel pump but no success!!

Then mate said change the spark plugs to be sure, so brought some cheaper NGK one’s ($22 all up for six)

Them problem is ALL GONE, must off been a dud spark plug

Worth a try!!!

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teazn_r33 Mentor

teazn_r33

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i have the same problem i had the car on the dyno i have a r33 gtst was tuning the air fuel and boostin it up and i was up to 282.3rwkw hoping to break 300rwkw was looking good and then it started to missfire i checked my ignighter pack and thet was shoot up the s@#t got another one and it still misfired.

i have gaped my plugs and all the other lil things mentioned

the car is all good when its cold then starts to heat up and starts again im guessing the coils wat are the best ones to use for this power figure... :P

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Angry Proficient

Angry

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Posted

im having the same issue with my rb20 ....brakes up around 4500 to 5500.... doesnt pull but mine ..after 5500 it pulls fine... but sounds liek a boxer for that 1000 or so rpm

hopefully this helps ya out..

http://www.skylinesaustralia.com/forums/in...2356&hl=misfire

it was in the general maintence section of the site.

Matt

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