Hi everyone

Is there any chance that my car wouldn't give a C.E.L after I install ACT prolite flywheel ? I have no lightweight crank pulley or etc.

If it gives a CEL does it stay always or go away after a while=???

Is there any chance to make it go away if my car gives CEL.

It's a mixed bag. Keeping at 12lbs or above is the "rule" to avoid the missfire CEL, but there are still plenty of above 12lb flywheel users that get it anyway, lightweight pulley or no. You are really taking a gamble, so my advice is to stick with stock to be safe or go as heavy as you can find, but not stock heavy.

So the cel goes away after some time or it always keep there?

I have an Exedy flywheel which weighs out to be about 12.5 lbs. supposedly if you stayed with 12+ lbs you were ok. I get the misfire codes after one or two drives (after clearing codes).....and they stay there. I had a lightened/underdrive pully which definitely made matters worse. I put the the stock pulley back on, it feels better but still get the codes.

I have the prolight flywheel from ACT and it comes and goes. It's very driveable no issues there but you do throw misfire CEL's I would say half of my time is spent with a CEL and half without due to my flywheel.

ACT ProLight and no CELs on my 04 STi

could be a newb response but doesn't the sti have 2 crankshaft position sensors and the wrx only have one? i've heard that this could be a problem.

well the number of sensors is not the problem.
But the weight of aftermarket flywheel.

sooner or later you will get a cel from the flywheel,
if you have a wrx.

so what does the aftermarket flywheel weigh for the STi?
if the manufacturers did their homework from the reported
cel from the wrx flywheels, sti flywheels will weigh more
than wrx flywheel.

9/10 times the reason you get a CEL from the lightened flywheel is from the RPMs coming down too quickly from high-RPM. To help not get the CEL, you can refrain from stepping on the clutch and letting your RPMs come down without any load.

ACT Prolite and no misfire CELs on my 05 STI.

I updated my ECU ROM via Enginuity to the latest issued flash, I don't get misfire cels on my 02 WRX anymore, although is will hesitate if I let the rpms drop without load as WeldingHank stated.