Richer mixture after intercooler upgrade?

[tomu80]

Since I've upgraded IC with FIMC AIRTEC I'm noticing decreasing LTFT (it's now -5,7% when it was 0% to +3,0% all the time before). It means that the fuel to air mixture is slightly too rich and ECU tries to compensate it. Is it normal?

If I measured it right O2 lambda sensor voltage is at higher levels on higher revs - on partial load (not on full boost). At idle it's fluctuating ok.

My guess is that AIRTEC IC can be in fact more restrictive than stock IC, so the air flow is more restricted = richer AF mixture = minus LTFT as an ECU answer for rich condition reading.

If not - what else could caused that minus LTFT? My car has 30 kkm on the clock and Oil Catch Can installed (to prevent valve carbon build up). K&N air filter is clean and spark plugs are new.

[Ragnarok]

Since I've upgraded IC with FIMC AIRTEC I'm noticing decreasing LTFT (it's now -5,7% when it was 0% to +3,0% all the time before). It means that the fuel to air mixture is slightly too rich and ECU tries to compensate it. Is it normal?

If I measured it right O2 lambda sensor voltage is at higher levels on higher revs - on partial load (not on full boost). At idle it's fluctuating ok.

My guess is that AIRTEC IC can be in fact more restrictive than stock IC, so the air flow is more restricted = richer AF mixture = minus LTFT as an ECU answer for rich condition reading.

If not - what else could caused that minus LTFT? My car has 30 kkm on the clock and Oil Catch Can installed (to prevent valve carbon build up). K&N air filter is clean and spark plugs are new.

Jamie is the right person to answer this, I am just throwing 5 cents based on my experiences. Feel free to correct me and tell I'm full of shit.

Cooler air should be more dense and thus it should actually require more fuel? Are you getting lower temps?
These ecus have only one LTFT for all loads and it might "live" when either cruising or WOTing for long periods. I noticed my Siemens ECU has different LTFT for different loads and even different banks.

Are you also sure you don't have a vacuum leak somewhere that could mess up the AFR? Also have you filled up your tank lately? Gas qualities vary.

[tomu80]

Air leak in engine with MAP sensors have no influence on mixture or LTFT. Besides, even in MAF engines an air leak causes mixture to turn lean (not rich).

Your idea about influence of colder/denser air is missed too - as there is more air ECU should enrich mixture to keep it's right ratio. So LTFT should climb up - not drop down. But thanks for your opinion anyway. :-) I'm wonder what Jamie can tell about this.