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Discussion Starter · #1 ·
Hey guys,

Just wondering if i can get some help/opinions on what could be the cause of my issue.

Its a Jdm K20a with a Rotrex C38-61 SC on it. Its recently been tuned and was running great for about a week.

Now its developed a bad misfire under WOT.

The Car drives good cruising around at low rpm with under 5% throttle, but as soon as i step on it.. The RPM climbs to about 3k and then starts misfiring/hesitating/sputtering. It is as if boost is just blowing the spark completely out.

So far i have tried:

- New TPS Sensor
- Different coilpacks
- Iridium Spark plugs heat range 7-9s with gapping from 0.032" to 0.020"
- Checked fuel pressure (datalogs show that it isnt leaning out or anything and AFRs stay fine)
- New MAP Sensor
- Air intake not clogged etc (Boost is being registered in datalogs, so there is no leaks)
- No leaks on my IM
- Quick visual check over most my sensor plugs that the pins were all still intact.

I think thats about it..

It started after i took the car for a 1hr drive; so heat may have been a factor. I also filled up my car with fuel. Could possibly be a bad batch? even though it drives fine on minimal throttle and cruising?

If you have an idea's id love to hear them!

Any help will be appreciated


Thanks


Ash.
 

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I would check the tune again.

I would have thought if you changed things like the TPS , MAP etc they would need recalibrating.

Not sure on your ebgine but OEM would be 6 spark plug range ?
7 is cold enough as thats what i run on my engine with the C38-91
 

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Discussion Starter · #5 ·
Yep i re calibrate the TPS every time i put a new one on.

I do have 7s in at the moment that i have gapped at about 0.025".

Im still thinking its a coilpack failing.. But ive tried other ones.. Unless my spare ones are buggered too.. :\
 

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is lean protection turned on? Are you using a primary o2 sensor? (OEM)

If your o2 sensor is failing the second you go near the gas it will lean cut. If you have a datalog that your willing to throw up, it will help everyone help you ;)
 

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Discussion Starter · #12 ·
Nope Lean protection is turned off. Yep using a Denso Wideband Primary 02.

Im using ID1000s and they are at about 30% when it is misfiring/cutting out.

HKS SSQV4 . And it seems to be holding boost in Kpro so i dont think its leaking out.. It doesnt sound like a boost leak..

It only happens under load whilst driving.. :/

View attachment more testing 2112.zip There is a short datalog. You can see where i go WOT and what happens..
 

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Nope Lean protection is turned off. Yep using a Denso Wideband Primary 02.

Im using ID1000s and they are at about 30% when it is misfiring/cutting out.

HKS SSQV4 . And it seems to be holding boost in Kpro so i dont think its leaking out.. It doesnt sound like a boost leak..

It only happens under load whilst driving.. :/

View attachment 33203 There is a short datalog. You can see where i go WOT and what happens..
Did you set your injector size in kpro?

EDIT: I also find it a bit odd that the second you go near WOT VTC rolls to 50*, Im not a tuner but I dont think thats right.
 

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Discussion Starter · #14 ·
Yep injector size is set to 1000. As i said though, the car ran really good for a week. Then after a long drive it began breaking up under load and is now at this stage which is quite bad.

Im not too sure on the VTC? I wouldnt know either.. My tuner didnt say anything about it..
 

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Discussion Starter · #15 ·
Ive tried new coilpacks, Kpro and added more engine grounds. All no deal.

Also been analyzing the datalog more, everytime the misfiring occurs, it is as soon as the cam angle rolls over to 50*... Hmmm.. both at 3500rpm and the vtec lower boundary is set to there as well.

Wondering if this is just a coincidence or could be causing my issue?
 

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Did you set your injector size in kpro?

EDIT: I also find it a bit odd that the second you go near WOT VTC rolls to 50*, Im not a tuner but I dont think thats right.
from what i recall the rotrex needs a good amount of timing, same goes for vtec killer setups, i'm no tuner either, but i know my vtec killer setup was similar where it ramped up timing then backed off up top...

had an issue with a friends car where it was doing the same thing.. problem ended up being a clog by the fuel pump.. doesnt hurt to check ya know
 

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Discussion Starter · #18 ·
Ahh right... Im starting to think it could be a timing issue as well.

Ive swapped over different fuel pumps/lines etc.. Im convinced now it isnt a fuel problem.. And my AFRs are still staying fine under a pull.

Another friend of mine is a tuner and he has played around with the MAP the other day. Raised vtec lower boundary to 4k and it has moved the issue to there now instead of 3.5k... hmmmmm..
 

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Do you have the original tune file? If so re flash it, im wondering if you accidentally made a change.

If you dont have it ask your tuner for the file he should have it.

from what i recall the rotrex needs a good amount of timing, same goes for vtec killer setups, i'm no tuner either, but i know my vtec killer setup was similar where it ramped up timing then backed off up top...

had an issue with a friends car where it was doing the same thing.. problem ended up being a clog by the fuel pump.. doesnt hurt to check ya know
ehh, 50* is alot, usually midrange is higher but after vtec hits its the lower side that makes the power.

OP What fuel are you running?
 
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