R33 Gtst Huge Flat Spot + Boost Cut

[MBar93]

Hey everyone

Recently I've been having troubles with my 33. I bought it last year, and at the time it was running 14psi, with a high-flowed stock turbo, and nistune-chipped ecu (not a great tune, runs rather rich). Had no problems when I bought it. Other mods the car came with were splitfire coilpacks, upgraded fuel pump, turbosmart bleed valve, FMIC.

A couple of months ago I added a Greddy type s bov (car was bought without bov), which I had a few issues with setting up, because I tee'd it to the same vacuum line as the boost gauge, and it leaked boost. I turned the boost down for a while until I got around to fixing it (this car is also my daily driver so it took a while), but now I've fixed that up and both now have their own source of vacuum. I then turned the boost back up to 14psi.

Lately, when at WOT I've been hitting boost cut when it spools close to 14psi in 3rd and 4th gear, and also there seems to be a massive flat spot which is very noticeable through 2nd gear, which wasn't there before and seems to be getting progressively worse.

I've already changed the spark plugs, as I thought maybe the rich-running engine might have fouled them and caused the engine to run excessively rich, although the old spark plugs were not fouled when I took them out and the new ones haven't made any difference.

Any ideas of what else could be causing this?

[SargeRX8]

Does it miss, cough or splutter at the rev range or just lose power? What is your boost gauge showing? Is your BOV plumbed back?

[MBar93]

It doesn't seem to be missing at all. No coughing or spluttering. Boost gauge shows about 13psi (I turned the boost down a little to try avoid boost cut). BOV is plumbed back

[MBar93]

Just another bit of info: an observation I made today was the flat spot starts at just after 4000rpm and continues until redline

[Dose Pipe Sutututu]

Could be the nistune falling into the knock map if it's Z32 ECU and the knock sensor mod on the board hasn't been done properly.

[XGTRX]

Are you running an airflow meter?

Block off the bov and see if it fixes it. If it does then I think the tune needs a bit of tinkering.

[MBar93]

Could be the nistune falling into the knock map if it's Z32 ECU and the knock sensor mod on the board hasn't been done properly.

The ecu is r33 gtst

Are you running an airflow meter?

Block off the bov and see if it fixes it. If it does then I think the tune needs a bit of tinkering.

It's running a stock rb25 airflow meter. I'll try blocking off the bov again

[tridentt150v]

R+R get a Z32 and retune.

[Dose Pipe Sutututu]

Are you sure it's a nistune OR just a re-flashed R33 ECU?

Because R33 Nistune Type-6 boards are still in prototype and I don't believe they have gone to market yet..

Anyhow, these days you can use a RB20DET ECU with the new feature pack that controls VCT woots

[sonicz]

Maybe the spark is giving out above 4000rpm. I know you have spitfires but that doesn't rule it out. Maybe you are running overly rich, fuel pressure regulator busted etc?

What spark plugs are you replacing it with? I hope you are not one of those guys that uses iridiums and gaps them down to 0.01mm. 0.8mm is low enough and use coppers.

The boost cut you are hitting because the AFM is running out of reading range. Nothing you can do about that unless you change to a bigger AFM, so just keep it under that point.

Edited September 23, 2015 by sonicz