I have an MY93 WRX with a switchable map, which allows me to select either the std U8 ECU or a ScoobyECU map.

I have noticed on colder days that the ScoobyECU struggles to start the engine when cold - it is very lumpy for a few seconds before the revs rise to about 1,400 rpm.

With the original U8 map selected, cold starting is fine - it cleanly revs up to around 1,100 to 1,200 rpm.

I'm guessing the ScoobyECU map is over-fuelling, but is there any reason for this?

It's not really a problem, because I start on the std map and switch over after a few minutes when I'm stopped in traffic, but I'm just curious as to why there is a difference? There is no difference between the maps when starting the engine from warm.

 

Not sure whats been done to your particular ECU but if it's a basic remap i.e not bigger injectors etc..etc..then ScoobyECU map is probably based around a Z4 ECU base map. No ignition, cranking, cold start or closed loop fuelling parameters would of been changed.

The only changes would of been to open loop fuelling/ignition, boost etc..etc...

It may be that you have a dodgey solder joint on the ScoobyECU or the motherboard where it slots in, which causes a slight problem when the ambient temperature is cold.

 

Thanks for the relpy Scott.
The ScoobyECU was from David Wallis, and as far as I know is a standard map for a TD05. I couldn't think of any reasons why the low end of the maps would be different, and you have confirmed they probably aren't.

I guess it could be a bad joint somewhere, but it seems strange that it only affects things for the first few moments when cold. I shall live with it for time being - glad I put the switch in now!