Z32 NA -> TT CR10.5 pistons, AFR spiking up and down

[Mika300zx]

Hey.

I have had this car 17 years now and it was brought to Finland from California. AT has been changed to new 5-speed MT (2005), EGR is deleted, AIV is deleted, PRVR is deleted and it has had Nistune since 2006 (I think). There's been no problems with it at all during these years and it has passed MOT / SMOG always with flying colors as NA.

I did that 1990 NA -> TT modification with z32 MT OEM turbos (new), Nismo 615cc injectors (new), CZP 200x180x115mm ARC Core intercoolers (new), GFB 3005 G-Force3 boost controller (new), OEM TT echaust manifolds (used), divorced 2.5" downpipes (used), JWT heavy duty street clutch (new) and AEM X-line Uego wideband lambda + controller (new). Engine was rebuilt totally 30.000 miles ago with 87.5mm CR10.5 CP pistons, new valves, new bearings etc etc. Cylinder head exhaust side was modified for better flow (OEM NA AT heads and cams). The AEM UEGO gives AFR information for the GFB boost controller.

Car is / feels very strong even the ignition is set to quite retarded on the whole map area (due to it was safe to drive to the dyno).

No boost leaks. Boost was 10.4 psi all the time from low rpm to rev limiter. Car gave with that boost quite low numbers: 280hp and 400nm (295ft-lb)

At the dyno we noticed after a while, when we were tuning the fuel maps and left the ignition maps alone, that AFR starts spiking up and down after 5000rpm. It goes approximately between 12.5 and 11.

What can cause this?

I had problems with the radiator fan at he dyno and the Nistune gave warning from the high engine temperature (95 deg celsius = 201 deg fahrenheit).

Is there some kind of safety feature in the ECU or in the Nistune which activates if temp goes too high and it causes this AFR spiking?

Thanks and Brgds Mika

[Mika300zx]

I forget to mention that car has NA AT ecu and it has now tuned TT program inside. Would it be better, if I put NA program back into the ECU and swap the tuned NA-TT fuel / ignition maps to it? Thanks.

[Matt]

What we really need is a log of the issue from the dyno (was it logged?) and a copy of the tune file

Otherwise without any further details from the logs, I am only guessing what it might be

High engine temp warning (95) is normal for that ECU

Some ECUs will add more fuel when high temp, but I don't think Z32 ECUs do IIIRC