So, I've been doing some reading, and wanted to confirm a few things.

There's only one O2 sensor on our car, just after the turbo. Is that right?

The intake air temperature - that should be part of the airflow meter, or a seperate sensor?

Detonation can also be a result of too lean a mixture? (sorry, I'm a turbo tuning newbie)

Curly,

Sounds like your AFM is suspect.
The air temp sensor is in the AFM on GC8's. Sounds like the ECU is reading the air temp too low and leaning out the mixture. The hotter the air, the richer the mix to compensate.
We've found faulty AFM's causing non start/detonation/mis fire problems on a few different types of cars.

Karl

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Thanks Karl,

I always thought that if the ecu thought the intake air temp was too low it would pump in more fuel, and advance the timing more aggressively?

Will try and get a pinout for the IAT and see if the problem is with the sensor or with the connection to the ecu...

From memory later model GC RA's (And maybe some Jap stis?) also had a seperate air temp sensor thats in the airbox.

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V5 & 6 (99-00) have a seperate iat sensor, mounted in the intake snorkel before the resonator.

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Other way round mate.
Warm air is less dense, so ECU puts more fuel in and retards timing. Cold air leans out mixture and advances timing.
Probably find it runs OK when the engine is cold as the ECU will be running on the cold start map. Once the coolant temp warms up, the ECU will revert to the normal map.

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I don't mean to argue with you, but cold air is denser (as you said), which means more molecules per volume. To keep the same A/F ratio, you add more molecules of fuel.
So if the air is warmer, you would put less fuel, as there is less air.
Why isn't that correct?

Adi

Cold start aside (which is based on water temp) the following is true:

Cold air = Ecu adds additional fuel over base map (as a positive % of injector duty).
Warm air = Ecu removes fuel (& timing depending on type of Ecu).

Disconnected IAT will result in rich AFR's....My powerfc, for example, will drop 3 full AFR numbers (from 15.4 at idle down to 12.4) with the iat unplugged (showing -40 in logs).

In Fc-Edit you can set the Iat LOW additional fueling & Iat HIGH ignition retard.

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ok, so if the IAT is disconnected or giving a low reading, that's going to result in crap fuel economy, but not an increased chance of detonation?

Roger.
My understanding is that more fuel will be added to suit the -40c air temp.

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