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HELP!! Missing above 4000RPM

Ronin 09

By Ronin 09,
in Engines & Forced Induction

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Ronin 09 Grand Master

Ronin 09

Posted
Posted

Hey everyone,

I did an engine, gearbox and diff oil change today on my R33 gtst, and took it out for a spin tonight. It was running really nicely, but when i took it above about 4500 RPM in mainly second it would hesitate, as if it was hitting a rev limiter or something.

It lost power but continued revving, but would miss - sounded like a braaaap! noise.

As a bit of background, all i have is a turbo back exhaust and air filter. Last dyno it was running peak boost of about 10.5PSI.

Its just a bit worrying and would like to get it sorted ASAP in case i am doing damage :D

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https://www.sau.com.au/forums/topic/17705-help-missing-above-4000rpm/
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Cubes Grand Master

Cubes

Posted
Posted

First I would pull the plugs out and check them for hairline cracks in the ceramic. Then Check their gaps.

Slap them back in and if you still have a miss either you have a dud coil or there is a hairline fracture in the plugs that you missed.

I had a similiar problem where it would drive nicely then at around 4000rpm+ it would start to pull then braaappppp brap brapp then if I held it down it would kind of smooth out and start pulling again. Generally once over 6000rpm to 7000rpm would be ok.. It turned out a hairline fracture in the spark plug. I had cracked it when slapping in No. 5 cyclinder spark plug as I tried to use a swivel and not remove the engine pipe across the engine.. SO if you do spark plugs don't do it the easy way and use a swivel remove the engine pipe so you have 180degree access to the spark plug. Otherwise you risk cracking the ceramic.

I had the plugs in and out around 4-5times before I found the problem.

Cubes Grand Master

Cubes

Posted
Posted

I think meggala's www site has a bit of info regarding using a multimeter to check them

Also check the springs that contact with the top of the sparky. If they are burnt or black chances are they are rooted. You can patch this up sometimes by removing that spring and using one from a pen. So i've read.. Don't know if it works or not though.

Cubes Grand Master

Cubes

Posted
Posted

I would be very very wary of doing that.. Have you ever been booted by an electronic ignition? I have it doesn't feel very nice.

I couldn't believe the boot it gave me actually. I've been booted by mains before and it was very close to that i can tell you.

  • 3 weeks later...
anish maharaj Newbie

anish maharaj

Posted
Posted

hey guys i have the same issue (96 s2) put a boost controoler on it boosted to 0.7 bar to be safe and car felt like crap..really jerky..winded boost back down and the problem kinda went.. but a mate/mechanic looked at it and said coils or fuel is too lean... gets checked out on wed hopefully not too much of a drama..am concerned.. should I b?

Zahos Mentor

Zahos

Posted
Posted

It happens b/c the mixture gets way too rich, when you are running higher than stock boost.

Changing the plugs can help reduce the problem, but it wont fully go away until you sort your mixtures out!

I recently got my SAFC dyno tuned, and at around that point, I had my mixtures adjusted by -21%!!!!!! So as you can see, it was running MEGA rich there!!!! Now there is absolutely NO hesitation/misfire/spluttering at that point, just smooh driving all the way up to redline!

Th only plugs that helped me before my SAFC tune were NGK coppers: BCPR5E gapped at 0.7 ~ 0.8 mm, but like I said, it wont cure the prolem. If you go any colder than a heat range of 5 (>5) then you will see no improvement.

Just passing on what I have learnt from personal experience!

Zahos

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