Maf Transfer off slightly; compensate with fuel stabilized table?

jruppert · May 12, 2007

I was just curious as to whether adjusting the fuel stabilized table to compensate for some maf transfer error is ok. My maf seems to be dead on from idle to around 3 volts. From 3 volts and up, it seems to run slightly lean. Can I make up for this by increasing my a/f in the fuel table? Does this efficiently work or should I continue to adjust maf?

final5-0 · May 12, 2007

Are you talking about wide band values being more lean than you would wish for during WOT conditions?

Grady

jruppert · May 12, 2007

Yes I am. I had entered 12.5 or so for my wot at high load for a/f and when it came time to driving it was coming out to being around 13.5 or so. I then went back into the table and entered around 11.5 and then finally my wideband showed around 12.1 - 12.5 at wot. Is this ok?

final5-0 · May 12, 2007

I like to use the greatest load row in that fuel table for WOT use.

I set it fat and the same in all cells.

I then use the part of the maf curve that is never seen in use during Closed Loop to make the value used in the fuel table match the value seen with the wideband.

After this is accomplished ... you can just change the value in that top row for what ever af ratio you desire

Grady

jruppert · May 13, 2007

The higher the value in the maf curve the richer it will be right? I did find yesterday that I went too far and once it hit around 10 the engine decided to stop making power.

final5-0 · May 13, 2007

Each point in the transfer is composed of a voltage and airflow value.

You raise or lower the airflow value but not the voltage value.

If you raise the airflow value in a cell, the pcm is gonna call for a
larger pulse width.

Grady

jruppert · May 13, 2007

I have noticed that at wot and high load my Duty Cycle reads around 87% and the PW is around 18. I wonder if this would effect my maf at wot.

final5-0 · May 13, 2007

jruppert said:
I have noticed that at wot and high load my Duty Cycle reads around 87% and the PW is around 18. I wonder if this would effect my maf at wot.

The Maf is used to determine pulse width at WOT along with the fuel table

I'm excluding any factors that might + or - fuel like the high speed enrichment
function you see in the Cobra.

Say you have your fuel table setup for WOT at 12 to 1

Say you flow 1000kg at 4.5 maf volts for maf point 26

Say you read 11.5 on your wb at that maf voltage

Your too fat at that point
so
You lower the airflow at that point
so
You then will command a lesser pulse width
so
You then will see a leaner display on your next WOT datalog

Make sense

Grady

Guero · May 14, 2007

Sorry to hijack. What if you A/F is dec3nt between gears 1-3, but at the end of 3 and the beggining of 4th you richen up to the 11's when before it was in the high 12's???

jruppert · May 14, 2007

yes it does make sense. i did find today while datalogging on the freeway that when i hit around 4 volts my maf seems to stop. is this normal?

jruppert · May 14, 2007

nevermind.. the maf was screwed up. i loaded up a new one and it went over 4 volts. i did adjust my maf from 3.0 volts to 4.0 volts and was able to get the a/f where i wanted it. i really had to fatten up those numbers. at first i wasnt sure if it was going to work because i was increasing them by so much.

final5-0 · May 14, 2007

Guero said:
Sorry to hijack. What if you A/F is dec3nt between gears 1-3, but at the end of 3 and the beggining of 4th you richen up to the 11's when before it was in the high 12's???

It could be fuel enrichment function

For the j4j1 it starts to come into play at 90 mph
and at 120 for the t4m0

A WORD OF CAUTION HERE

This thread is important!

this area of fuel management is where very little margin of error takes place
and
one could do damage
so
you want to be certain this stuff is understood

If I have not explained myself all that well
or
If anyone has any kind of Q's ... I'm happy to give more specifics if needed

Grady

Guero · May 14, 2007

And another reason I haven't played with that part

final5-0 · May 14, 2007

Guero said:
And another reason I haven't played with that part

I understand
but
No need to be intimidated

When doing stuff you are not sure about
I did tons of it btw

Have a good datalog for a baseline

Make a very small change and only 1 change

Do another dlog exactly the same as the baseline dlog and use the
newest dlog as verification that things work like you suspect they do.

Hard Data
Its your friend
Use it to your advantage

Grady

Maf Transfer off slightly; compensate with fuel stabilized table?

jruppert

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