I have a version 4 STI, which I think means the ECU is not mappable. I also have a HKS vta fitted, which from the various threads I've seen on here is more than likely why my car is running rich on the over run. Not an issue as it sounds great through the Blitz nur spec R I have just fitted.
However, would a front mount intercooler help to lean the mixture off a little. Just thinking that cooler/ denser air may help, or am I barking up the wrong tree.
Cheers.
Matt.

 

Barking up the wrong tree, logic is totally wrong.

 

Yeah, is that because the air from the recirc dump valve isn't actually metered and is just a given? As in the only way to sort the fueling is to buy a recirc dump valve or get a different ecu and have it mapped with the vta. Little confused as when I had my last scoob vta's were a good thing supposedly, but now they're out of favour.

 

Not quite. The reason why the fuelling goes wrong with an externally venting dumpvalve is because the dumped air has been metered. The ECU still expects it to be present and will calculate fuel accordingly. Because your atmospheric dumpvalve has exhausted the bypassed air, there's now less air in the system than the ECU thinks, so you get too much fuel.

However, that has nothing to do with the reason why your FMIC idea was a bad one. You seemed to be approaching it from the point of view that the atmospheric DV causes rich running on lift-off (which it does), and so fitting an FMIC will lean the mixture a bit.

It might do. The trouble is it might lean it all the time, including when your foot is down, with the consequence of introducing lean on-boost running. In addition, to fit an FMIC you'll need to remove the standard airbox and fit an induction kit, which introduces the likelihood of further airflow measurement errors. In other words you'd be introducing new and potentially more significant problems than the one you're trying to address.

You could just live with the lift-off overfuel. although if you do want to sort it out, the easiest way is just to get hold of an OE spec dumpvalve. Should be pretty cheap to get hold of and certainly a far more cost-effective way of curing lift-off overfuel than shoving on an intercooler you don't need.

Don't know whose posts you were reading then but they've always been a bad idea. They might have been in fashion with some of the chavvier elements of the community (and as such might have suffered some post-chav backlash), but from a technical point of view, an atmospheric venting dumpvalve has always interfered with the optimal running of the engine - at least when using standard-ish management. Nothing's changed in that respect.