VE table effect on WOT fueling?

[Bill@HPTuners]

having a discussion on another board about this...would just like to know the facts. Were talking about commanded vs. actual a/f ratios...my impression has always been if your ve & maf tables are correct your commanded pe should be pretty close to your actual a/f...and that the problem with gtp's or boosted fbodies is the map runs out at 140 so the computer is kinda guessing over 140kpa, am I correct in my thinking?

[viper04af]

having a discussion on another board about this...would just like to know the facts. Were talking about commanded vs. actual a/f ratios...my impression has always been if your ve & maf tables are correct your commanded pe should be pretty close to your actual a/f...and that the problem with gtp's or boosted fbodies is the map runs out at 140 so the computer is kinda guessing over 140kpa, am I correct in my thinking?

i was told to add fuel with my PE table...... but i know after 100 it only uses the last vavleu... i would also like to know exacly how all this interlaces

i was told to add fule with the PE table and PAT (linxs) put all his to 35 after the block where he has boost but to me this doe not see mlike the best way to add fuel???? does that just not tell the PCM that at 35% TSP the car it WOT?> how does that add fuel...... i can see it adding more fule dow nlow but not up top.....

i would thin k i woud need to adjust the VE table in the boost rpm's and using the add the fuel needed in that... say buy making it 150%

HPT guys?

[Chris@HPTuners]

the VE table/MAF is used to determine airflow, the PE table is used to set the commanded AFR.

Once you hit the limit of the VE/MAF table it will stick with the last value. Then your only choice to command more fuel is by commanding a much richer AFR than necessary to make up for the low airflow estimate the PCM is using. ie. you may command 10:1 AFR to actually get 12:1.

to determine the injector pulse width the PCM uses a caluclation like this:

InjPW = (GramsAir / AFR) / injector flow rate

GramsAir is calc'd from the MAF or the VE table
AFR is the commanded AFR (so GramsAir/AFR = GramsFuel)
The divide by the injector flow rate in GramsFuel/sec to give you the InjPW in seconds.

You can see from this that at the end of the day the only thing that matters is the InjPW and either fuel or air side can compensate for each other if need be.

Chris...

[Bill@HPTuners]

the VE table/MAF is used to determine airflow, the PE table is used to set the commanded AFR.

Once you hit the limit of the VE/MAF table it will stick with the last value. Then your only choice to command more fuel is by commanding a much richer AFR than necessary to make up for the low airflow estimate the PCM is using. ie. you may command 10:1 AFR to actually get 12:1.

to determine the injector pulse width the PCM uses a caluclation like this:

InjPW = (GramsAir / AFR) / injector flow rate

GramsAir is calc'd from the MAF or the VE table
AFR is the commanded AFR (so GramsAir/AFR = GramsFuel)
The divide by the injector flow rate in GramsFuel/sec to give you the InjPW in seconds.

You can see from this that at the end of the day the only thing that matters is the InjPW and either fuel or air side can compensate for each other if need be.

Chris...

so if you were to mess with the ifr table cells for wot you should be able to get the actual # to be closer to the commanded if I understand that right.

[Chris@HPTuners]

you could use the PE table or the IFR table, remember the IFR table is used ALL THE TIME and not just at high RPM. If it were me i would use the PE table.

[Bill@HPTuners]

you could use the PE table or the IFR table, remember the IFR table is used ALL THE TIME and not just at high RPM. If it were me i would use the PE table.

normally the only time i use the ifr is to adj. for larger injectors...and use the pe for wot fueling...a few of us were wondering if there was any way to get the commanded closer to the actual so you could make adjustments via pe relyably after it was intially tuned with a wideband...with v8's i would think its possible with a good speed density tune & maf scaling the commanded should be very close to the actual...but with gtp's being out of the ve range I wasnt sure if it was even possible...my commanded differs from my actual by 4-10% depending on the cell.

[viper04af]

you could use the PE table or the IFR table, remember the IFR table is used ALL THE TIME and not just at high RPM. If it were me i would use the PE table.

so should i leave the VE table all 80's stock and use the PE to dial in the AFR ? right now the Ve table is scaled up to 150 to add fuel if that not working i'm ing to put it back down lol

[Chris@HPTuners]

on the V6's the VE table is only used if the MAF fails if it isn't failing cos you set the fail freq very high then it is never used. Personally i would leave it high "just incase".

Chris...

[viper04af]

well i copied in a 98 VE table and even set my command up from 7ARF to 9.5 and its working fine.....

[OneSlowGTP]

Isn't the VE table also used to "check" for MAF failure? Having a VE table that isn't accurate, couldn't that cause the PCM to think* the MAF has failed, and switch over to the inaccurate VE table?

If your IFR is correct, and your MAF is accurate, What tables would you change to fine tune AFR?

Why are VE values on a 3800 N/A much higher then that of the 3800 S/C ?

on the V6's the VE table is only used if the MAF fails if it isn't failing cos you set the fail freq very high then it is never used. Personally i would leave it high "just incase".

Chris...

[OneSlowGTP]

the VE table/MAF is used to determine airflow, the PE table is used to set the commanded AFR.

to determine the injector pulse width the PCM uses a caluclation like this:

InjPW = (GramsAir / AFR) / injector flow rate

GramsAir is calc'd from the MAF or the VE table
AFR is the commanded AFR (so GramsAir/AFR = GramsFuel)
The divide by the injector flow rate in GramsFuel/sec to give you the InjPW in seconds.

You can see from this that at the end of the day the only thing that matters is the InjPW and either fuel or air side can compensate for each other if need be.

Chris...

Because my Driver information Center does not display an accurate MPG estimate, I wanted to run an experiment.

I changed the IFR table by 200% making the PCM think I had huge injectors thus cutting the InjPW by 1/2

I then scaled the MAF table to read 200% as well, so the PCM would command twice as much fuel for the injectors that spray 1/2

The car wouldn't even idle and kept dying without giving it gas...

I thought mabye this was because the car was in Open Loop.... I tryed using the VCM Control section to force Closed loop...

Didn't work.

What am I missing here?

[OneSlowGTP]

GramsAir is calc'd from the MAF or the VE table

Chris...

If GramsAir is being calculated from the VE table instead of the MAF table, what does the formula look like?

Thanks,
-Andy

[Bill@HPTuners]

If GramsAir is being calculated from the VE table instead of the MAF table, what does the formula look like?

Thanks,
-Andy

[maf.metric]*(120/[HPT.NUM/CYL])/(engine speed) er something like that

[OneSlowGTP]

[maf.metric]*(120/[HPT.NUM/CYL])/(engine speed) er something like that

I was looking for the formula to calculate it without using the MAF. Strictly the VE table.

For example:

with a MAP kPa pressure of 100
and an Engine RPM of 2400
you get a VE value of 74 (using the stock GTP table)

now...... Given that information, how would that translate to g/sec or lb/min of air?

looking at some logs, I'm thinking the answer should be pretty close to: 9.3lbs / min

I imagine the formula takes static values such as a 3.8L engine consumes x amout of air per RPM, and at 74% efficency it will be y amount of *actual* air.

Formula would be nice,
Thanks
-A