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Help With Boost Drop Off Between 5000-600rpm?

85URK

By 85URK,
in Engines & Forced Induction

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85URK Grand Master

85URK

Posted
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Hey guys, i have R33 gtst 95 model, rb25det engine, anyway car is basicly stock turbo, stock computer, has 3" turbo back exhuast, greddy fmic, avcr b/c, split fire coilpacks, walbro 255L fuel pump installed, now if im travelling along at 60km/h drop it back to 3rd or 2nd and flatten it, goes through the rev range fine until it gets to 5000rpm then it feels like it drops off power until about 6000 rpm then comes on full power again until redline at 7200rpm, now i dont know much about the avcr i have it set up on self learn mode, i have been told that its not the best way to run it, but i just got it set up so it goes to all stars and left it so it was safe, running 10psi which is about right with what a standard car would run with ungraded exhaust on it. still does has this problem at that boost. any ideas??

Cheers

Daz

R-SPEC Grand Master

R-SPEC

Posted
Posted

my car does this aswell

but mine is a r34 gtt auto and doesnt have the mods you do, pretty much stock.

revs up smoothly till it gets to about 5k

although depends what gear its in. 1st and 2nd gear revs all the way smoothly. this happens in 3rd and 4th

also curious to find out what causes this...

85URK Grand Master

85URK

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plugs are gapped down to 0.8mm, unless they have opened up in the last 3000km since i changed them at my last service, and also

The R+R thing seems to be what its doing, but on the avcr it wont drop boost below 10psi coz that's what it runs standard now with the exhaust and extra flow. i have got it running pretty much the lowest boost it will with the standard wastegate.

RBwhatever Veteran

RBwhatever

Posted
Posted

Either get a safc II as a cheap fix so you can trick the AFM readings so it won't drop in to R&R, or go the half hog and get a piggy back ECU or go the full hog and get a replacement ECU and get it tuned.

Getting it tuned will change the way you car feels. It's worth the dosh

85URK Grand Master

85URK

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I have a power fc sitting here ready to go in, but was going to wait till i got bigger turbo and injectors first. so dont wanna get it tuned yet. the thing is it never really did this before i had fmic and avcr and fuel pump installed, so its gotta be one of these things that are causing it to do that.

RBwhatever Veteran

RBwhatever

Posted
Posted

Yes, well a tune will fix your problem though. Your standard ECU is having trouble trying to manage all these new changes you've added to the car, its freaking out and trying to play it safe at the expense of your fuel and performance.

R34~neo6~turbo Contributor

R34~neo6~turbo

Posted
Posted

i have the same problem on my r34 neo gtt b4 but mine is totally stock in the hood but same with you its cutting from 5k -6k then goes smooth from there. my problem was the spacings on my plugs, when me and tony took it out and put new 1's in with the .8 spacings problems went away.

85URK Grand Master

85URK

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i have the same problem on my r34 neo gtt b4 but mine is totally stock in the hood but same with you its cutting from 5k -6k then goes smooth from there. my problem was the spacings on my plugs, when me and tony took it out and put new 1's in with the .8 spacings problems went away.

thanx for that. i will be replacing the plugs again soon. so il post in here if its fixes the problem. i actually have coppers in there at the moment and gapped them down to 0.8 , they have only been in for 3000KM but i will put the iridiums back in maybe this weekend, see if its changes it at all. the gaps on the coppers might have opened up in that 3000KM and could be causing the problems.

85URK Grand Master

85URK

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noob question but how do you "gap" them?

well, when u buy plugs they come with a different gap sizings between where the tip of the plug is where it arks to, you have to get some feeler gauges, which come in different size gaps you put them in between where the tip is and where it arks out on the plug and tap the plug gently against a bench or something so that the gap will decrese in size to the size of the gauge. that makes it easier for the spark to travel across the distance bcoz its not as far for the spark to travel. normal copper plugs u buy are usually about 1.1mm gap, the iridiums are already gapped down to a 0.8mm so you shouldnt need to touch them.

RBwhatever Veteran

RBwhatever

Posted
Posted
well, when u buy plugs they come with a different gap sizings between where the tip of the plug is where it arks to, you have to get some feeler gauges, which come in different size gaps you put them in between where the tip is and where it arks out on the plug and tap the plug gently against a bench or something so that the gap will decrese in size to the size of the gauge. that makes it easier for the spark to travel across the distance bcoz its not as far for the spark to travel. normal copper plugs u buy are usually about 1.1mm gap, the iridiums are already gapped down to a 0.8mm so you shouldnt need to touch them.

Well you can buy them pre gapped. Iridiums do come as a 1.1mm. So if you want .8's you buy .8's, if you want 1.1's you buy 1.1's.

85URK Grand Master

85URK

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Well you can buy them pre gapped. Iridiums do come as a 1.1mm. So if you want .8's you buy .8's, if you want 1.1's you buy 1.1's.

yeah u are right i think. lol but i really have never bought 1.1 for my car in iridiums, not really worth it in turbo cars.

RBwhatever Veteran

RBwhatever

Posted
Posted
yeah u are right i think. lol but i really have never bought 1.1 for my car in iridiums, not really worth it in turbo cars.

yeah I bought 1.1's for mine and haven't experienced a problem with them. But for everybody else, may as well just cut the crap and go for .8's. Spark plug gap arguments are another topic by itself so I won't raise it in here :P

85URK Grand Master

85URK

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Well today i got to and managed to change the plugs back to my iridiums from the coppers i had in there gapped down to 0.8, and now that the iridiums have been sandblasted and cleaned by me at work, there like new again, and work great. rev's all the way through the rev range now without hesitation, cheers guys, i had a feeling it might have somehting to do with the copper plugs. but seriously they were only in for 3000km and the gaps must have increased or something, i thought they woudl have atleast lasted the 5000km but turns out they didnt, but they plugs werent that dirty either.

RB JET Apprentice

RB JET

Posted
Posted (edited)

I had the exact same problem in my 33. The car feels like it bogs down in that rpm range (feels like going through wet sand or something), so i purcahsed power fc, got it tuned and it now runs great, pulls hard all the way to redline!!! Your pretty lucky that it was plugs, it wouldve saved me a lot of money if it was the problem with mine!!

Edited by RB JET

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