ULTM8Z

Is this the IAT enable switch that tells the ECM that you're running a duct mounted IAT?

Reason I ask (and not sure why I didn't notice this before), but all the factory bins I have show this switch being enabled even though they have the coolant style MAT sensor mounted in the plenum.

AUJP, ANHT, AXCN, AWFU, and others.

BDLZ, BDLD ('93 LT1 Camaro also has this enabled too), and they had duct mounted IATs...

So I'm a little confused now...

RBob

iTrader: (1)

It is the difference in using the intake duct heating model or just the CTS & MAT:

https://www.thirdgen.org/forums/diy-...sation-8d.html

RBob.

ULTM8Z

Yeah I actually posted in that thread... the thing is I thought the switch you were taking about was the enable inv mat table switch.

Is it not?

RBob

iTrader: (1)

I believe it is the same switch as you are posting about?

RBob.

ULTM8Z

So then my question is why do the factory TPIs have it enabled? Doesn't enabling that switch mean you're specifying the intake tract model for IAT (per that link above)?

RBob

iTrader: (1)

The thread linked above explains it a bit. Even though it is a MAT, at low air flows the chamber charge is going to be at a higher temperature. Using the heating tract table allows to compensate for this.

RBob.

ULTM8Z

Reading through that thread for probably the 56th time... I may want then to disable that table and use the T term as is with no adjustment for airfllow...

Non metallic air tube with a heat shielded air filter sitting completely outside the engine compartment, and very short runner manifold... my guess is there is negligible contribution of coolant temperature to the air temperature.

Hmmmmm.... just when I thought I starter to understand this MAT stuff...

ULTM8Z

Hmmm, I guess that is the switch... I found it Tunerpro with the following description...

1 = Use Table L880E to determine gm/sec air flow ( Stock AUJP)
0 = Bypass Table
before calculating L006D=MAT, CYL VOL & SCALING TERM, which is used to calculate BPW in the Fuel Minor Loop

IMAT= Inverse MAT Lookup Table Enable
b4 is used to select either the intake tract heating model table_L880E,
T = ((CTS - MAT/IAT) * MULT) / 128 + MAT/IAT
or to just use the MAT/IAT as is...
T = MAT/IAT

ULTM8Z

RBob, so another question... (sorry if this was explained in earlier threads already)...

In a different thread, you had posted that

https://www.thirdgen.org/forums/diy-...offset-vs.html

Post #9

So then if O2 (mV) = Counts x 4.42

Then for the MAT Compensation Counts table, does that translate to this? (picture below). This is the AUJP MAT Compensation Counts Table, and they O2 mV column I added is taking the Counts column and multiplying by 4.42.

The hotter the air, the less dense, thus less fuel required... so then at say, 56C (133F), is the ECM literally biasing the O2 sensor reading lean by 424 mV? That seems like A LOT given the range is only 0 to 1V. IF not, then what exactly is the ECM doing with this O2 mV number?

RBob

iTrader: (1)

No, that is not how the results of the table look up(s) are used.

RBob.

ULTM8Z

well don't leave me hanging... lol...

how are they used?

RBob

iTrader: (1)

https://www.thirdgen.org/forums/diy-...ml#post2063451

"The ~T term is used in the calculation of the mass of air in the cylinder. It compensates for the air density change due to temperature."

RBob.

ULTM8Z

Yes Understood... I'm just trying to understand where the "counts" go and how they'e used. I can take the counts and convert them to O2 mV, but not where that goes after that...

maybe I'm not asking the question correctly?

RBob

iTrader: (1)

Only way to answer this is to explain what the code is doing:


Starting at the beginning the MAT value is loaded into reg A: LDAA L0063

That is used as the lookup argument into the MAT compensation table. The result of the lookup is returned in Reg A. This is the "COUNTS" value.

Reg B gets loaded with 128, then the two are multiplied together. This is Reg A with the result in it, multiplied by 128 which is in Reg B.

The result of the multiply uses both Reg A and B as a Double to hold the result of the multiply.

Then some scaling is done, which is seen by adding $7480 (29824 d) to the result of the multiply.

The PSHB, PSHA, PULX transfers this result to the X register.

The Double register is loaded with the CYL Volume parameter (LDD L86DD). Which is then divided by the scaled MAT term (FDIV).

That result is saved in L006D (STX). Which goes to calculate the GM/SEC airflow.

Note the population of the MAT compensation table. As the MAT increases so does the COUNTS. The higher the COUNTS the lower the result from this routine.

Basically, the result is the inverse MAT, scaled, with the cylinder volume divided by it. So the higher the MAT temperature the smaller this value is.

RBob.

ULTM8Z

Holy smokes... guess I asked for it!

Thanks RBob... I'll have to read through this and (try to) digest it. Probably will have more questions...

ULTM8Z

So I'm still not sure I fully understand what you said, RBob...

So if I'm doing all of my math right here.... (and that's a big IF!... lol… )

The corrected T term for an engine operating at 80°C coolant temperature is, where I'm picking the 96 multiplier since it corresponds to the lowest airflow value for idle speed.

T = ((80-15)*96)/128+15 = 64°C

So GM is saying that in roughly a few seconds, the air temperature is going to go from 15°C to 64°C? Even for a TPI I find that hard to believe…

For BDLZ $DA3 LT1, (multiplier = .398 x 16 = 51), the corrected T term is 41°.

At WOT, the difference is only a couple of deg (as expected given the air is moving so fast). Though given a heat soaked stock sensor in the plenum, I can’t see it reacting that fast to take advantage of the cooler air temps during a short WOT burst.

So it’s no wonder the car runs so much better with the LT1 Inv MAT table after relocating the sensor.

I'm going to try disabling the Inv MAT table and see what happens when the ECM is not factoring in the coolant temperature into the air temperature calculation.

ULTM8Z

Interesting….

After disabling the Inv MAT table, I’m finding that I’m having to dial back the AE delta TPS vs coolant and delta MAP vs coolant values. My baselines for those were the LT1/LT4 values, but slightly increased at higher coolant temps to get the throttle response in line.

However, after I disabled the Inv MAT table, I noticed fairly large rich spikes on the WB during off idle, with even a slight stumble. There were also large rich spikes during transition to WOT between 2000 and 3000 rpm.

I ended up putting the AE vs coolant back to factory LT1/LT4 and the throttle response smoothed back out.

I can’t say that I noticed any real increase in power or anything like that, just that I’m using less fuel on the AE to get the same crispness in the throttle response.

Of course, the ambient temperature has been pretty mild around here last few weeks, so I’m not sure what’ll happen in the middle of summer (unless another heat wave rolls through before winter sets in).

But, same power using less fuel is always a good thing (especially now that idiot-infested Looneyfornia just slapped us with a &!@#-ing 12-cent gas tax so they can continue to fund government union employee benefits and pensions... err... I mean highway maintenance.

Seems like overall, my take-away from this is that if you have a fairly well-insulated cold air tube (i.e., one that's not made out of metal) with relocated MAT sensor, it's probably better to not have to play guessing games with the Inv MAT table trying to tailor the multiplier term vs the calculated airflows. Rather it's better to just not have the ECM start mixing in coolant temperatures with the measured air temperature.... just take the raw air temperature and tailor the fuel to that.