GTR flat spot question

[GTaaargh]

Since I received my new GTR from Japan I have had a flat spot between 2,000 and 4,000. It seems to be mostly around 3,000 rpm.

The ECU has been modified by garage SAURUS. For some reason it will stay in closed loop until 4,000 rpm. I guess it is one of their tuning tricks - or maybe it's trying to keep the fuel economy reasonable.

The turbos have certainly been upgraded, but I do not know what was done to them.

I also get turbo surge at 3,200 rpm occasionally, but do not know if it is related to the flat spot issue.

I know one of the oxygen sensors is slow.

I hooked up a laptop and a PLMS adapter to the diagnostic port and noticed that one of the RB20 AFMs was at about 2 while the other was at 2.5 when it was going lean.

A competent mechanic has looked at it and cannot find any air leaks.

I strongly suspect that it is not just a badly set up car. Someone has spent a lot of money on good gear, and I do not believe he or she would have accepted changes that affected the drivability at road revs - especially if it was something as simple as the fuel map being modified by a company as prestigious as garage SAURUS. If I cannot find any other solution I will try getting the fuel map modified, but would really appreciate suggestions on what else might have gone wrong.

I've put up another posting about modifying the fuel map.

[ferni]

Sounds like what mine does but only when its cold for the first minute or two of driving, then something changes (assuming ecu changes from closed to open loop mode?) and its smooth. I barely notice it since i'm hardly on the throttle until my oil temp starts warming up and by then its gone.

[doubled]

could your car have different cam's or even the cam timing slightly out.

[GTaaargh]

Yes. It appears to have different cams. It certainly feels 'lumpy' when it is idling.

The turbo comes on strong early, which is apparently indicating that I have at least exhaust cams.

Would different cams make it go lean?

[Sydneykid]

What I would do....

First job, clean the AFM's, I use brake cleaner as it leaves no residue. Then recheck the voltages. Once you have consistent readings stick it on the dyno, connect all the dyno sensors (inc knock) and do a power run. Then have a good look through the graphs, particularly boost, knock and A/F ratios.

Garage Saurus are known for agresssive tuning and they use 100 octane fuel. So it is important to make sure the tune will handle 98. Flat spots and compressor surge are all tuning signs. Don't fark about, if it is lean and advanced you will kill it very quickly.

[GTaaargh]

What I would do....

First job, clean the AFM's, I use brake cleaner as it leaves no residue.  Then recheck the voltages.  Once you have consistent readings stick it on the dyno, connect all the dyno sensors (inc knock) and do a power run.  Then have a good look through the graphs, particularly boost, knock and A/F ratios.

Garage Saurus are known for agresssive tuning and they use 100 octane fuel.  So it is important to make sure the tune will handle 98.  Flat spots and compressor surge are all tuning signs.  Don't fark about, if it is lean and advanced you will kill it very quickly.

AFMs were cleaned by the competent mechanic. Prior to that I did a dyno run which has a nice rich (and uneconomical) mix all the way through.

By the way, the dyno-dude said he couldn't adjust the tune because the ECU had been modified. If a dyno shop cannot adjust entries in the ECU, how can they adjust advance etc? That's probably a really dumb question, but I'm still learning.