New feature: GM AIT conversion

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tlcoll1
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New feature: GM AIT conversion

Post by tlcoll1 »

Here's a new feature. When using the GM MAF with the ECU+ (or MAF translator, for that matter) to replace the stock MAS, you also lose the stock barometric pressure sensor and air temperature sensor. To compensate for this, the ECU+ includes fixed voltage outputs that can simulate fixed barometric pressure and air temperature.

The baro sensor isn't that big of a deal, as most folks drive their car in areas where the baro doesn't change all that much. The air temperature is a bigger deal, as temperature variations are common, especially with this crazy "seasons" thing and that whole "night and day" thing.

But good news. The ECU+ now includes the ability to convert an aftermarket GM air temperature sensor so that its readings match that of the stock air temperature sensor. This means that if you can plumb in a GM AIT sensor, the ECU+ can make it look like stock.

Thanks to Joe M (AWDSM97) for verifying that a previously-unused ECU+ input can be used for this. (The ECU+ has two such inputs, BTW.) If anyone would like to give this new feature a whirl, e-mail me and I'll send you instructions and the new software.

Tom
Attachments
The conversion screen.
The conversion screen.
gmaitcnv.jpg (49.07 KiB) Viewed 20262 times

honki24
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Post by honki24 »

Cool, good to know you're still alive and tunin' :)
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Deepnine
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Post by Deepnine »

One question:

I thought a gm maf will compensate for temperature and pressure by itsself. thats the reason why you set input on the ecu to a fixed value.

and then another thing:

where do i install the ait sensor in a blow thru setup? at the gm maf or before the turbo?

tlcoll1
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Post by tlcoll1 »

No, the MAF doesn't compensate by itself, thus the need for this new feature. Using a fixed voltage is usually "good enough" but not perfect.

Tom

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Post by Deepnine »

i don't understand it.
on mitsu mas there are 3 values: air volume, air pressure and air temperature, with this the real amount of O2 is calculated.

the gm maf is a hotwire right?

hotwire's output frequency it not volume, because the air volume is different in normale mode and blow thru mode.
before the turbo 2 litre air, are the same like 1 litre after, with the right boost pressure.

the output is the real value of air molecule per time and the boostpressure does not matter. intercooler efficiency is also different on every set up. then why does the airtemp does matter?

maybe i don't understand how a gm maf works or i miss something.

tlcoll1
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Post by tlcoll1 »

I believe the GM MAF uses the same Karman Vortex principle as the stock MAS and is not a hot-wire type. The main advantage of the GM MAF is the lower restriction of the air path. When you remove the stock MAS, you're removing the integrated air temperature and barometric pressure sensor, and thus losing that part of the air flow freqency -> air mass calculation. This feature adds the air temperature back into the equation.

Tom

honki24
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Post by honki24 »

Does this enable me to log intake air temp via the GM AIT? Can I log it externally or is it automatically going to override the stock MAS's air temp reading?

I'd like to continue to let my stock air temp sensor do its job, but I'd like to weld in a GM AIT just before the throttle body to see my intake temps. Will this feature facilitate that?

Also... any idea where to get one or does anyone know the part number? I've found that RRE sells 'em... but their site isn't very friendly and I'd like to compare prices.
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Deepnine
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Post by Deepnine »

tlcoll1 wrote:I believe the GM MAF uses the same Karman Vortex principle as the stock MAS and is not a hot-wire type. The main advantage of the GM MAF is the lower restriction of the air path. When you remove the stock MAS, you're removing the integrated air temperature and barometric pressure sensor, and thus losing that part of the air flow freqency -> air mass calculation. This feature adds the air temperature back into the equation.

Tom
If a GM MAF is a Karman Type, then it couldn't be possible to change the possision between blow throu and draw throu.
The Karman Vortex alone just measures the air speed.

With aditional temp and pressure sensors you can calculate the air mass flow. In german the formula called "adiabatische Zustandsgleichung".

But with air speed alone and even air temp, you can't change the operation mode form draw throu to blow throu, because the density changes as soon as boost levels rise. That would give a error factor about *2 for every 14,7 psi. With this error the engine would stop immediately.

So the GM MAF must do the pressure calculation alone, and the only thing it does this by its self is a hotwire. hotwire also does the temp calculation.

I have read something about a coldwire GM uses, but i haven't found enough information how it works.

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Post by rogersmith »

Honki, I was going to get a sensor too and do what you plan to. I'm sure you can wire the sensor to one of our analog inputs. You'll just have to convert the voltages in your head or in excel, unless Tom decides to program in a selection for GM air temp sensor.

honki24
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Post by honki24 »

rogersmith wrote:Honki, I was going to get a sensor too and do what you plan to. I'm sure you can wire the sensor to one of our analog inputs. You'll just have to convert the voltages in your head or in excel, unless Tom decides to program in a selection for GM air temp sensor.
Well... I won't do it unless he's able to program the ECU+ to be able to log it... which really shouldn't be hard I should think since he already has the scaling. I could use that spare ACD input that I read about on EvoM... but I want my ECU+ to log everything. I don't want to go back to using some stupid evoscan or mitsulogger usb logging software in conjunction to my fantastic ECU+. :wink: So many wires ought not be running through the cabin of a racecar.
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tlcoll1
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Post by tlcoll1 »

honki24 wrote:Does this enable me to log intake air temp via the GM AIT?
Right now it's just an option that allows the ECU+ to regenerate a simulated stock AIT signal and you can't log it. I'll put logging on the to-do list.

Tom

honki24
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Post by honki24 »

I'll put the AIT sensor on the "to do list" ;)
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AWDSM97

Post by AWDSM97 »

yeeeaa Im the guy its originally for but I havent been able to using it because Im trying to get my car to run right...pretty soon though!

Deepnine
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Re: New feature: GM AIT conversion

Post by Deepnine »

I have to bring this up again, it makes me sleep bad. :D

I hocked up two GM MAFs.
One in blow through mode between intercooler and throttlebody.
And another between airfilter and turbo.

Now i measured the output frequency of both, there was no difference. Both showed the same.

The first (before turbo) one had 14,7 psi absolute, 25 celsius.
The other (after turbo) on had about 22psi absolute (14,7 psi atmospheric + ~8 psi from turbo) and 45 celsius.

There should be some difference in frequency because of pressure and temperatur difference.

I can't say if it's exactly because i don't have the right equipment, but i think it worked.

Thats means the GM MAF must be an Hotwire, were air temperature and barometric pressure are included in the output frequency. If you wire in a intake air temperature sensor, the ecu will add fuel on cold days and run leaner on warm days.

I thing the effect is minimal but it should be about 1,7% per 5 degres celsius, from 25 celsius.
30 celsius airtemp will subtract 1,7% fuel.
20 celsius airtemp will add 1,7 fuel.

Maybe i totally miss something, but that all confused me.

tlcoll1
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Re: New feature: GM AIT conversion

Post by tlcoll1 »

Interesting observation.

I'm not a thermodynamics guy, but from that perspective, it seems like you're right. But... let's think about this a different way. Take a looong pipe (say 1000 feet) with a GM MAF at one end and a GM MAF at the other end. The pipe has no leaks. On the far end, light a fire under the pipe. Blow cold air into the near end. At the far end, the air will be hotter due to the radiated heat from the fire. By your reasoning, the GM MAF should read differently on the two ends due to the temperature difference. I think, instead, that they read the same because the GM MAF is essentially measuring the "wind speed" of the air, and that's the same no matter what the temperature or pressure is within a closed system.

Something to think about at night...

Tom

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