leirch

On the 730ecm, I was reading an older post that Glenn replied to saying how complicated the inverse MAT lookup table was, it was explained as to how it works but I'm still having problems understanding how compute gm/sec so I can start compenstating for air temperature changes.

If somebody could explain the process I would appriciate it.

Thanks,
Brendan

Craig Moates

I've got a MAT question too.

On MAF cars, is it used in any way?

And if not, can we use that input for something else? (ie. WBO2)

TRAXION

leirch: Check out the ANHT Hac. It has the calculation for VE and you can backtrack to the MAT inverse table.

Craig: On MAF cars it is only used for EGR enable. If you aren't running EGR then you can use the input for whatever you want For MAF cars the MAT is not used for fuel trim.

Tim

Grim Reaper

I will assume that you've read this

https://www.thirdgen.org/techbb2/sho...hreadid=100049

I will not say anything more about how the MAT Inverse Blah-Blah-Blah Table works because I thought I had it all figured out but I know I don't. There is something more to it and I don't have the time to completely read it all at this time.

I say this because about 6 months ago I tried an experiment to COMPLETELY recalibrate the Inverse MAT table and the BIN MAT table so I could use the FULL RANGE (instead of the half range that is currently used). It was a complete disaster and I was lucky for my "backup" eprom.

For the time being, I would follow the MAT table I've posted in the post above and "retrim" your Injector Constant and VE Tables. That MAT table is extremely reliable for a relocated MAT.

Once I get "back into the source code" of the $8D and spend more time analyzing the MAT, I will post the interrelationship between the Inverse MAT Table, the Bin/Temp MAT table and whoe it all works (plus a few other routines that I am curious about). But I have limited time right now with work and family commitments. Not enough time in a day.

Oh yeah, the MAT doesn't work on MAF cars as Tim said - only controls the EGR. So yes MAF cars could possibly use it as another input device. Just make sure that you either have disabled your EGR by setting it to $FE (if you aren't using one). Or if you are using an EGR, make it work all the time by setting the Enable temp to $00. If you get into the "code" you could also consider swapping the MAT for the CTS sensor. And just wait for it to hit "proper operating temps".

leirch

Thanks for the info Trax and Glenn, I checked the hac and the old post, after reading it about 3-4times I finally realized how to use the comp counts to correspond to the inverse table,

now, wouldn't it make more sense to change the boundries on the comp counts to the same boundries that the inverse table has? its very confusing trying to determine which range your in and which range your not in.

leirch

ttt

Dave_Jones

Resurrecting an old thread, I know...but for anyone who might be interested, I did a little ECM bench testing on some of the Inverse MAT stuff tonight.

As a preface, two related threads for reference:
https://www.thirdgen.org/techbb2/sho...hreadid=100049
https://www.thirdgen.org/techbb2/sho...threadid=37854

Anyway, I was using a slightly altered AUJP; inj constant at 26.1, EGR enable temp maxed out, most DTC's disabled, basically stock otherwise, to include the MAT and VE stuff.

Testing method, was to hold 1000 RPM, 44.5 KPa, 176°F ECT. Also, 10% TPS, and 20 MPH, to stay out of idle.
MAT was varied, used 40.6°F, 110.9°F, and 150.6°F, which equals 5, 44, and 66°C. (I've had odd results from my scantool trying to read temp in °C, so I scan in °F -- sorry for mixing units)
At each MAT, I messed with the Comp Counts, and Delta Mult tables, and Inverse Term Lookup Enable, and observed the change in BPW.

Summarized observations:

Inverse MAT Term Lookup "IMTLU"

1. Disabling IMTLU always resulted in more fuel.

2. At higher MAT temps, the fuel difference was minor.
(e.g. BPW 2.59 vs 2.64 ms at 66°C MAT; a 2% difference)

3. At lower MAT temps, the difference was much more significant.
(BPW 3.25 vs 2.79 ms at 5°C MAT; a 16% difference)

4. Whether or not IMTLU was enabled, had a big deal to do with the other two MAT tables.

MAT Compensation Counts vs. MAT Table
let's call it "Comp Counts" for short:

1. A lower number in the table gets you more fuel.

2. Comp counts had a larger impact on fuel than Delta Mult.

3. If IMTLU is enabled, the comp counts table value that has the impact, is NOT the table entry that corresponds to the MAT value. It's the next two or three higher temp entries that have the effect! (this might be why it'd been previously posted that Comp Counts has only a minimal effect -- if IMTLU is enabled, and you mess with the table value where you'd expect it to matter, i.e. corresponding to your MAT temp, nothing happens. This was definitely the biggest surprise of the evening. Edit: actually, leirch mentioned it two posts above this one, but I had no clue what he was talking about until now )

Example, when MAT is 4°C, IMTLU enabled, BPW is 2.79 ms.
Go into the Comp Counts table, and change the closest value, which is 8°C. Nothing happens. Matter of fact, change ALL the entries all the way from -16°C to 32°C. Push 'em up to 255, or whatever. No change in BPW! Now change only the table entry for 44°C from the stock value of 84 to 42, and BPW jumps to 3.17 ms, a 12% change! Gonna have to stare at the hac for quite awhile before I understand that one!

4. If IMTLU is disabled, the Comp Counts table value that causes the change, corresponds to the real MAT value. i.e. if MAT is 44°C, and you change the table entry for 44°C, BPW now DOES change. And in this case, chopping the 44°C value in half as above, from 84 to 42, makes for almost the same change in fuel, with BPW increasing 13%.


Inverse MAT Term Lookup Delta Mult. vs. Airflow Table
I'll refer to it as "Delta Mult" for short.

1. A lower number in the table gets you more fuel. (as stated in previous posts)

2. If IMTLU is disabled, this table has no effect. (as one would expect)

3. Scaling the table, appeared to make much more of a % change in fuel at low MAT temps than high.

I'm too tired to post all the numbers, unless anyone really wants to know.


Just for kicks, I entered Glenn's Delta Mult table, from the reference threads, and compared it's output to the stock GM table.

Observed BPW with MAT at 100°F, other conditions same as before:
Still at 100°F MAT, but MAP now 50 Kpa, 25% TPS:
MAP increased to 75 Kpa:
Didn't have time to test things at other MAT temps, but you can at least get a glimpse at how the fueling compares. Looks like at higher airflow (RPM & MAP) Glenn's modified Delta Mult table provides just a bit more fuel than stock, but less fuel at lower MAP & RPM. I'll try to run some different MAT temps tomorrow, to see if that trend holds across the board. I also want to vary the coolant temp, and try to see how the difference between MAT and ECT affects things.

HTH,

87_TA

Good info DJ and glenn from previous efforts,
I was just going to post that just thist last week I actually disabled MAT lookup because I honestly think I will have better results.
Wow did I get rich in a hurry, So I figured no big deal it should be a global change - that was not the case at all which confused the heck outa me.

Now I have it all squared away again after a few days and will see how badly temp changes effect.

Actually if somebody know how much air density changes for say every 10 degrees in temp drop that would help alot.
I may try to start rescaling the tables as temp changes, I guess making 47 degrees my 0 mark.

Grim Reaper

Here is another post regarding my revised MAT Tables. I always suggested that a person would be wise to "rescale" their VE tables as when I did all of this testing, it was using my setup with my fuel pressure and my VE Tables...so I always suspected that if you wanted to use my MAT Table that a person would be wise to rescale their VE Table as Dave as pointed out.

Also, it's operating range was fro 0*C to 110*F with the relocated MAT. Maybe with RBobs, calculations someone can come up with a revised MAT table based on the stock AUJP bin. But, always remember that unless your engine is "bone stock", you will always need to revise your VE Tables.

Even Fuel Pressure will greatly affect VE Tables. I have found the Fuel pressure has it's greatest effect at the higher Kpa values of the VE Tables and least effect at the lower Kpa values.

The real key, is to make sure that people realize that they should always re-scale the VE Tables if they make any mods to their engine in ALL Kpa & RPM ranges.