MAF scaling or injector scaling/latency
 

Im about to tune this 05 MR with GT30 and a bunch of mods, including intake/intake pipe and upgraded injectors (the owner of the car doesnt know the exact cc). They are scaled at 713 in the ROM. I dont know if the scaling is correct, cuz most of the tune is "weird" and "off". The MAF scaling is still stock.

Now the LTFT low is pegged at +12.6. LTFT Mid and LTFT High are near 0

I know that I need to either

-adjust the injector scaling and latency

-rescale the MAF to compensate for the intake and piping

What I dont know if which method should I use to correct the fuel trim? MAF or injectors? Or both? If both, what one do I start with first?

TIA

Assuming the WOT is correct, then latency is the key. If the whole thing is wonky then it will be a combination of both. Latency is your idle/cruise correction (more or less) independent of your WOT fueling (scaling...more or less).

What about scaling the MAF? I think i read a quote by you about how you dont believe in rescaling the MAF , IIRC. But people say if you have an intake/intake pipe you need to rescale your MAF. Whats your take on it?

Ummm I dont believe in rescaling the MAF :lol:

It affects too many other things that we have only begun to get into to. Most of the time it will only affect where the MAF puts the load, and it is usually very linear. For instance the HKS & ARC induction box makes a car read VERY low from where it should be for the airflow actually going through the MAF. Some go the opposite way and make it ALOT higher than where it should be.

I just tune the car where it actually is and dont sweat the details.

So, to fix the fuel trim issue, I should just use injector latency(& maybe scaling) right?

Correct.

K thanks.

also, I couldnt tell if you were agreeing or not about that you dont like to change the MAF scaling. Seemed like you were saying that you DONT like rescaling the MAF.

Aaron doesn't like to/doesn't mess with MAF scaling... period. As long as the fuel trims are + or - 10% then good to go... set it and forget it...

Okay. Yeah, Im feeling like its a better idea to leave MAF scaling stock.

If a hardpipe is causing issues it will throw off both the load low and low freq MAF values (because MAF frequency used in the ROM is calculated from load). What load value range are you getting at (a decent) idle? Is it a stock-ish load value?

It idles around 30 load, which seems pretty normal to me.

That is normal to every evo i have logged.

I sometimes, rarely, but sometimes mess with MAF scaling. I haven't found anything over 13% off but if so i usually get it <10 closer to 5%. It isn't difficult and i just smooth the curve from the adjusted idle and cruise values to the other values. I don't typically touch anything over cruise.

Another option is to change the MAF compensation table. (MAF Adjusment is what I call it). By increasing by only 1 point you affect fuel trims by 5-8%. For those of you that are way out on your fuel trims, a minor tweek here could help.

JohnBradley,
Have you ever used latency on stock injectors to correct low and mid LTFTs? I am running stock injectors with an open cone filter and my LTFT's are pegging at 12 and 9 for low and mid.

cant that be related to your fuel table cell values??

NAB