Car 'Stuttering'/'Coughing' on boost problem II - GT-R Register - Official Nissan Skyline and GTR Owners Club forum

ru' · 18th August 2008, 03:22 PM

Further to previous post, I hope someone can help.

When hot, my car sort of 'coughs' when I floor it. It's fine at lower temps etc. So far I've checked the plugs, coilpacks are splitfires, coilpack cover has been removed, earthing kit fitted. Car runs V Pro with MAP (i.e. no MAFs).

It does it maybe once going up the rev range (doesn't feel like coilpack failure to me). Like "brrrrrrrrrrrrrrrr short gap rrrrrrrrrrrrrrrrrrrrrrrrr!" (lol at the explanation). As you can imagine on full throttle, it doesn't feel like its doing the car any good when it 'coughs'.

I don't know if it's a cause or symptom, but the boost drops for an instant when it 'coughs'/'stutters'.

Could it be my (oem) dump valves on their way out, or an odd pressure/temp sensitive boost leak somehwere? Or, if it was something like ignition cut, would the boost drop momentarily anyway?

It seems okay with the boost controller (greddy profec II) set at 1 bar, but not when set at 1.4 bar.

I hope someone's got an idea, or could point me in a direction for further fault-finding.

Cheers,

Ru'

Asim R32GTR · 18th August 2008, 06:04 PM

Sounds like you need some new sparkplugs.
Did you try to gap them? to 0.8mm ?
What type plugs are you using?

Asim

ru' · 19th August 2008, 07:21 AM

Plugs are fine (and recently replaced) sadly. Greddy ones (8 heat range, probably 0.8 gap).

dazman · 19th August 2008, 01:04 PM

Hi Ru i know youve covered a lot of simple things that could cause the problem but from threads ive read before and own personal past expierence it normally is 1 of the simple things. You say youve checked plugs but have you replaced them again? you never know there could be a air line crack in 1 that is not visible but under pressure and increased heat it opens up and causes a prob(youve always got a spare set then if it aint the prob). Are you near anyone to swap coilpacks over and give it a blast? Have you re-checked all pipes again. Only by re-placing or swapping the parts can you truley eliminate them from the equasion.

ru' · 19th August 2008, 03:50 PM

Cheers Dazman, that's excellent advice. I guess I need to a) stop being lazy, and b) stop being tight lol.

You know how it is when you convince yourself that it can't be x, y or z etc. despite the symptoms pointing that way.

I may just take it down to GTaRT and get them to investigate, but every time I go near that place I blow loads on mods...

dazman · 19th August 2008, 04:03 PM

I know exactly what you mean mate,i think sometimes we look at things too technical

like i said a spare set can always be used on ya nxt service,so really it aint cost you out to try

KEEP OUT of the sweet shop for a little while or you will be drawn to the Dark Side

Lend those coilpacks and then move on to the nxt thing

sometimes i dont make a lot of sense but im quite proud of meself on this one LOL

ru' · 19th August 2008, 10:24 PM

I vote that GTROC should have a set of splitfires plus an ignition amp to be loaned out to members for fault-finding... (er, of course I'd have to renew my membership first...)

18th August 2008, 03:22 PM	#1 (permalink)
ru' New Users Join Date: Feb 2007 Location: Black R33 GTR V-Spec Posts: 1,901	Car 'Stuttering'/'Coughing' on boost problem II Further to previous post, I hope someone can help. When hot, my car sort of 'coughs' when I floor it. It's fine at lower temps etc. So far I've checked the plugs, coilpacks are splitfires, coilpack cover has been removed, earthing kit fitted. Car runs V Pro with MAP (i.e. no MAFs). It does it maybe once going up the rev range (doesn't feel like coilpack failure to me). Like "brrrrrrrrrrrrrrrr short gap rrrrrrrrrrrrrrrrrrrrrrrrr!" (lol at the explanation). As you can imagine on full throttle, it doesn't feel like its doing the car any good when it 'coughs'. I don't know if it's a cause or symptom, but the boost drops for an instant when it 'coughs'/'stutters'. Could it be my (oem) dump valves on their way out, or an odd pressure/temp sensitive boost leak somehwere? Or, if it was something like ignition cut, would the boost drop momentarily anyway? It seems okay with the boost controller (greddy profec II) set at 1 bar, but not when set at 1.4 bar. I hope someone's got an idea, or could point me in a direction for further fault-finding. Cheers, Ru'

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18th August 2008, 06:04 PM	#2 (permalink)
Asim R32GTR GTR Register Member Join Date: Sep 2003 Location: Norway / Oslo Posts: 928	Sounds like you need some new sparkplugs. Did you try to gap them? to 0.8mm ? What type plugs are you using? Asim

19th August 2008, 07:21 AM	#3 (permalink)
ru' New Users Join Date: Feb 2007 Location: Black R33 GTR V-Spec Posts: 1,901	Plugs are fine (and recently replaced) sadly. Greddy ones (8 heat range, probably 0.8 gap).

19th August 2008, 01:04 PM	#4 (permalink)
dazman GTR Register Member Join Date: Mar 2007 Location: Staffordshire Posts: 208	Hi Ru i know youve covered a lot of simple things that could cause the problem but from threads ive read before and own personal past expierence it normally is 1 of the simple things. You say youve checked plugs but have you replaced them again? you never know there could be a air line crack in 1 that is not visible but under pressure and increased heat it opens up and causes a prob(youve always got a spare set then if it aint the prob). Are you near anyone to swap coilpacks over and give it a blast? Have you re-checked all pipes again. Only by re-placing or swapping the parts can you truley eliminate them from the equasion.

19th August 2008, 03:50 PM	#5 (permalink)
ru' New Users Join Date: Feb 2007 Location: Black R33 GTR V-Spec Posts: 1,901	Cheers Dazman, that's excellent advice. I guess I need to a) stop being lazy, and b) stop being tight lol. You know how it is when you convince yourself that it can't be x, y or z etc. despite the symptoms pointing that way. I may just take it down to GTaRT and get them to investigate, but every time I go near that place I blow loads on mods...

19th August 2008, 04:03 PM	#6 (permalink)
dazman GTR Register Member Join Date: Mar 2007 Location: Staffordshire Posts: 208	I know exactly what you mean mate,i think sometimes we look at things too technical like i said a spare set can always be used on ya nxt service,so really it aint cost you out to try KEEP OUT of the sweet shop for a little while or you will be drawn to the Dark Side Lend those coilpacks and then move on to the nxt thing sometimes i dont make a lot of sense but im quite proud of meself on this one LOL

19th August 2008, 10:24 PM	#7 (permalink)
ru' New Users Join Date: Feb 2007 Location: Black R33 GTR V-Spec Posts: 1,901	I vote that GTROC should have a set of splitfires plus an ignition amp to be loaned out to members for fault-finding... (er, of course I'd have to renew my membership first...)