Relocated MAF and need re-tune!

[04gibbstahoe]

I am trying to fix my tune on my 09' GMC Canyon with the 5.3 engine. I recently built a custom intake tube for it and now it runs like crap on the factory tune. I used an aluminum maf adapter tube which allowed me to ditch that factory odd shaped plastic tube that holds the maf sensor. The inner diameter of the new aluminum intake tube is different than the factory plastic intake tube and I would assume this is why the truck runs differently now. I have done minimal tuning on some of the gen III stuff, but I just read the pcm on my new truck and I am totally lost on this gen IV stuff. Not even a VE table to edit..... I am lost.....

The truck does not really idle all that bad, but the drivability is horrible. The throttle sticks/hangs badly at low speeds and cruising. Posted a criusing log if it helps.

I don't really know where to begin on air flow adjustments for the gen IV stuff. Any walkthroughs for dummies out there?

[eficalibrator]

Putting the OEM MAF element into a new housing is the same as replacing the entire MAF assembly as far as the ECU is concerned. You need to recalibrate the MAF transfer function and everything should come back in line. In short, force it into open loop and MAF-only operation, the correct the MAF curve based on steady state error readings from a wideband and commanded AFR/lambda.

[04gibbstahoe]

Putting the OEM MAF element into a new housing is the same as replacing the entire MAF assembly as far as the ECU is concerned.

Good to know. I did not realize changing the housing would have impacted the flow readings as much as it did. I don't have a wide band because I dont realy plan to do any other mods besides the intake for now.

Can I not log LTFT/STFT percent error vs MAF(hz) or something like that? What are the steps to correct my fueling using fuels trims?

[BBA]

Yes, you can do it with narrowband. You will have to disable PE/DFCO/LTFT and run in forced closed loop mode. Log MAF hi and low tables vs STFT and make corrections as needed then relog. I have done several MAF size changes this way, not an issue. (Of course most dyno tuners around here will argue the point about wideband vs closed loop tuning, but it's only because they only know one way to do it).

If you have increased the size of the air flow housing, you can shortcut the process by calculating the size increase and creating a ratio to correct the MAF table to start with, then do fine tuning with MAF/STFT. You can also rough it in by multiprying the entire table by 10% at a time until the idle is right, then finish off with the rest of the MAF tune process (wideband or cloised loop/narrow band).

[IDRIVEAG8GT]

In my experience, the factory MAF curve is what you'll want to stick with so far as an air model. Find how far off one particular cell is, then multiply the entire table by that percentage value. That will bring fueling across the board back in line, as a simple air volume change pretty much has the same effect in efficiency for any increase or decrease in the dynamic flow of air, UNLESS you located your MAF in a bend in the intake tube...... Which is a no-no.

[patooyee]

So how did it go?

[patooyee]

Yes, you can do it with narrowband. You will have to disable PE/DFCO/LTFT and run in forced closed loop mode. Log MAF hi and low tables vs STFT and make corrections as needed then relog. I have done several MAF size changes this way, not an issue. (Of course most dyno tuners around here will argue the point about wideband vs closed loop tuning, but it's only because they only know one way to do it).

If you have increased the size of the air flow housing, you can shortcut the process by calculating the size increase and creating a ratio to correct the MAF table to start with, then do fine tuning with MAF/STFT. You can also rough it in by multiprying the entire table by 10% at a time until the idle is right, then finish off with the rest of the MAF tune process (wideband or cloised loop/narrow band).

I'm new to this and need to tune my MAF. I have seen this described and am interested to hear Greg's stance on it. I have no opinion as to if its acceptable or not so please don't feel that I am questioning your judgement. I do have a wideband so I can do it either way.