Engine Doesnt Idle After .08mm Gap

[DRFT 14]

I have a NEO RB25DET S14 Silvia conversion. Mods are - LinkPlus ECU, large turbo and all related boltons except injectors. I took the car to get tuned recently, but got a disappointing call from the tuner saying the motor wouldn’t rev past 4500rpm and he cant diagnose the problem. He loaded an R33 base map on the LinkPlus and I drove it home. The car starts and idles beautifully. Under 4500rpm it drives as smooth as a stock motor. Anywhere past 10psi however results in the aforementioned misfire/revlimit.

On the way home from the dyno, the car surprisingly revved to redline with no problems, which made me wonder what the tuner was going on about. The next day, I got in the car for another test drive, and sure enough it wouldn’t rev out past 4500rpm - just like the tuner said. It now occasionally revs to redline on 1st gear but never on any higher gears. The tuner suggested to try gapping the sparkplugs down to. 08mm. I tried this today but the car now doesn’t even idle with the gapped plugs. I removed the plugs, spaced the gaps back to normal and it fixed the problem. I find this very surprising, as ive never heard of gapped plugs disrupting idle?

I took the car for a drive and grabbed my camera. Below is a video that shows the misfire. Hopefully someone might recognise the problem? Notice how 1st gear rev limits and backfires at around 6000rpm. 2nd gear the motor simply doesn’t rev and sounds very weird, almost as if the wastegate is venting on and off? 3rd gear the same thing happens so I quickly change gear. The last clip I added to show how 1st gear occasionally decides to rev out nicely.

http://s2.photobucket.com/albums/y27/DRFT1...nt=MissFire.flv

Id love some help on this. The project has really stalled at this stage.

[240dreams]

I once had an issue on the dyno. We were doing 4th gear pulls and my speed cut was kicking in at 112MPH (179KMH). Therefore it enabled a fuel cut way before redline.

I'm don't think that this is your problem since you said it doesn't happen in 1st at times but it's a thought.

Are you running the correct heat range spark plugs?

[Craved]

looks alot like coilpack issues to me, though that wouldn't explain any issues with 0.8 gapped plugs

notice alot more black smoke out the back of the car when it is missing? i see more when mine does it, unburnt fuel.

[chrissso]

Hey Buddy,

Is that Link plus ECU a piggy backtype?

If so, then, I remember someone saying that fuel cut on an NEO engine is around 9-10psi. You might not be hitting more than 10psi in first gear. Try winding the boost back. - Just a thought.

[DRFT 14]

I should have said that im running wasted spark, so its not a coilpack issue. I tried new leads and brand new NGK Platinum spark plugs but that wasnt the problem.

The LinkPlus is a complete engine management system, not a piggy back so I wouldnt suspect a fuel/speed cut.

The boost issue is an interesting one, as it only seems to be cutting out after 10psi. The ECU is setup with a basemap for an R33, could this be the issue? Maybe the increased air flow from the large turbo at 15psi throws the tune way off? But in saying that, I doubt that would result with the engine being unable to rev like it does?

Are you guys able to view that video? Any thoughts on it?

[ferni]

Try copper plugs gapped to .8mm ... plats sometimes missfire when they are gapped a bit lower...

[DRFT 14]

looks alot like coilpack issues to me, though that wouldn't explain any issues with 0.8 gapped plugs

notice alot more black smoke out the back of the car when it is missing? i see more when mine does it, unburnt fuel.

Speeking of unburnt fuel, I noticed black drops of liquid sputtering from the muffler while it was idling yesterday. I tried smelling it but couldnt identify what it was. This especially happened after a changed the gap to how it was before the .08mm gap which didnt work. Could this be unburnt fuel? I find it pretty unlikely that fuel in its liquid form managed to travel all the way from the injectors and out my exhaust pipe though?!

Does that hint at anything? (The motor wasnt missfiring while idling)

[BezerkR32]

what boost controller are you running? Sounds like boost cut. the reason it doesnt do it in first gear is because it doesnt see as much load, therefore less boost. Ive heard factory boost soleniod on Neo engine limit boost in lower gears. May be worth bypassing factory solenoid and running an afternarket ebc. Never seen ignition brake up at 10psi and doubt plug gap would be an issue at that boost either. Whos tuning it?

Speeking of unburnt fuel, I noticed black drops of liquid sputtering from the muffler while it was idling yesterday. I tried smelling it but couldnt identify what it was. This especially happened after a changed the gap to how it was before the .08mm gap which didnt work. Could this be unburnt fuel? I find it pretty unlikely that fuel in its liquid form managed to travel all the way from the injectors and out my exhaust pipe though?!

Does that hint at anything? (The motor wasnt missfiring while idling)

Edited May 28, 2006 by BezerkR32

[DRFT 14]

Im not running a boost controller at this stage. The wastegate spring limits boost to 15psi. Im going to take it for a tune a different tuner after exams are over.

[DRFT 14]

Anyone get a chance to the view the video? Any thoughts on the gap issue?

[TTT]

Did I misread or did you say you gapped it down to 0.08mm??

normal gaps are 1.1mm and most people reduce the gap down to 0.8.. not 0.08

you may have mis typed it but I'm sure you 0.08mm more than 2 times.

please confirm.

gap should be 0.8mm NOT 0.08mm

[DRFT 14]

Thanks for clearing that up GTST. A mate of mine told me it was 0.08. Even though I was pretty sure it was 0.80, I took his word for it.

Anyway, now gapped it to 0.8 and it idles fine. Misfireing issue is still not sorted though. Il ask again if anyone has any ideas after the viewing the video. If not, il take it to another tuner and have another go (even though I run the risk of getting hit with 75% of the tuning bill and come home with an un-tuned car like the 1st time). I took it back to my electirician, he went over it thrice and is certain there is no issue with the wiring or anything related to that. I tend to agree with him, if the car idles fine and runs great below high boost, surely it cant be an electrical fault? Im about to tear my hair out with this one!

[MKDR33]

might be ur coil packs..

this thread might help ---> http://www.skylinesaustralia.com/forums/in...howtopic=119403

[R33S2]

I hope this is not your problem but I had a car that did this same thing, turned out to be a hairline crack in a inlet valve housing to water jacket, it only did it when the motor was working, ie if I stopped for awhile it would be ok untill engine reached a certain level (temp didnt move much) it eventually opened enough to fill a cylinder, that shot into the air when I cranked it over lol (no plug motor wouldnt turn over).

[DRFT 14]

Cant be coilpacks, its running wasted spark. R33S2, thats seems like a worst case scenario. I really hope its nothing like that! Il keep it in mind though if we dont find a solution..

[satanic]

One of our customers with a R33GTST had a mis-firing problem; he had the stock coil packs and 0.8mm iridium spark plugs.

We fixed the problem up by gapping these to 0.75mm - all solved.

I think he was experiencing constant mis-firing at anything above 4,000RPM.

Hope this is a little bit of help

[DRFT 14]

Interesting how such a small gap difference can solve/cause missfiring issues. Il have a go at reducing the gap by .05. Il let you know how it goes

[satanic]

Hopefully it works on yours... just to add more information,

We tried new plugs at 1.1mm, new plugs at 0.8mm and then re-gapped the old plugs to 0.75mm

Third time lucky~

[Hakai]

Thanks for clearing that up GTST. A mate of mine told me it was 0.08. Even though I was pretty sure it was 0.80, I took his word for it.

Anyway, now gapped it to 0.8 and it idles fine. Misfireing issue is still not sorted though. Il ask again if anyone has any ideas after the viewing the video. If not, il take it to another tuner and have another go (even though I run the risk of getting hit with 75% of the tuning bill and come home with an un-tuned car like the 1st time). I took it back to my electirician, he went over it thrice and is certain there is no issue with the wiring or anything related to that. I tend to agree with him, if the car idles fine and runs great below high boost, surely it cant be an electrical fault? Im about to tear my hair out with this one!

I don't know alot about this sorta thing, hell I don't know alot about anything really but I do know that 0.08mm is a Gnat's dick of a gap. Perhaps when you gapped them that small you damaged the electrode and thus when you gapped them back to 0.8mm they won't work properly?

Just a thought.

[The Dan]

Are you sure it's a misfire? Many people just use this term for lack of a better descriptive word. Won't rev over 4500 grand would indicate that it won't, or has trouble, revving over 4500 grand, not misfire. Check basics first like fuel pump (pressure and flow). So many of you are concerned with a spark issue but it takes more than spark to make a car run.

CHECK BASICS!