map ecu - air temp sensor explanation?

[carendt242]

can someone w/ some EFI knowledge clear up a few q's i have.

1) Purpose of air temp sensor
do i have this right - main ecu uses air temp as a factor in determining fuel map. colder air = denser air = slightly more fuel being added to compensate. with map ecu, this remains unchanged - we have no control over adjustments made by the ecu for air temp.

does this sound right?

what are the pro's of disabling the temp sensor using a resistor?


2) Location air temp sensor
the instructions say put it in turbo inlet pipe; i read this as "stick it between air filter and turbo." correct?

wouldn't it be more accurate to stick it post intercooler to account for turbo heating & IC cooling? looking at the VPC instructions, they replace the fuel filter w/ the temp probe - seems like air temp is being read in the intake manifold.

why do instructions say turbo inlet and not manifold? what are pro's & con's of each approach?

i would guess it has to matter - the heating & cooling of air doesn't seem like it would be linear (i'm too lazy to research this & forget high-school physics..)


meth injection - i intend to use derek's kit at some point and it seems like people using VPC's have trouble if the temp sensor is too close to the injection point; for this application, it seems essential to have air temp sensor in manifold.


3) How would i read air temp from manifold?
let's assume this is the best approach - how would i do it? or should i just drill a hole immediately in front of the throttle body for the sensors?


thanks,
chuck

[Veta]

Originally posted by carendt242
can someone w/ some EFI knowledge clear up a few q's i have.

1) Purpose of air temp sensor
do i have this right - main ecu uses air temp as a factor in determining fuel map. colder air = denser air = slightly more fuel being added to compensate. with map ecu, this remains unchanged - we have no control over adjustments made by the ecu for air temp.

does this sound right?

what are the pro's of disabling the temp sensor using a resistor?


2) Location air temp sensor
the instructions say put it in turbo inlet pipe; i read this as "stick it between air filter and turbo." correct?

wouldn't it be more accurate to stick it post intercooler to account for turbo heating & IC cooling? looking at the VPC instructions, they replace the fuel filter w/ the temp probe - seems like air temp is being read in the intake manifold.

why do instructions say turbo inlet and not manifold? what are pro's & con's of each approach?

i would guess it has to matter - the heating & cooling of air doesn't seem like it would be linear (i'm too lazy to research this & forget high-school physics..)


meth injection - i intend to use derek's kit at some point and it seems like people using VPC's have trouble if the temp sensor is too close to the injection point; for this application, it seems essential to have air temp sensor in manifold.


3) How would i read air temp from manifold?
let's assume this is the best approach - how would i do it? or should i just drill a hole immediately in front of the throttle body for the sensors?


thanks,
chuck

The same question was posted by me. We must wait for answer Powerhouse;)
My idea was - for stock ecu temp sensor / stock position at air-filter ........ but m friend told me to he has ask at anybody selling MAP-ECU and the aswer was : intake manifold

I see it better too, but what will make the serial ECU with it? If you have snad alone OK - but oem ECU? Who knows?

[carendt242]

technosupra & obiwan responded to this thread (well, i received emails saying they did) but i don't see any responses here on the forum... crap...

would you two mind re-posting? (or i am the only one experiencing this problem?)

[Veta]

Originally posted by carendt242
technosupra & obiwan responded to this thread (well, i received emails saying they did) but i don't see any responses here on the forum... crap...

would you two mind re-posting? (or i am the only one experiencing this problem?)

I have not received any e-mail about new answer of this thread.

But im still waiting for some explain from PHR?
And the set of plugs is still not by me home:( (i dont speek abou 20cm snow)

[8secsupra]

Originally posted by carendt242
can someone w/ some EFI knowledge clear up a few q's i have.

1) Purpose of air temp sensor
do i have this right - main ecu uses air temp as a factor in determining fuel map. colder air = denser air = slightly more fuel being added to compensate. with map ecu, this remains unchanged - we have no control over adjustments made by the ecu for air temp.

does this sound right?

what are the pro's of disabling the temp sensor using a resistor?


2) Location air temp sensor
the instructions say put it in turbo inlet pipe; i read this as "stick it between air filter and turbo." correct?

wouldn't it be more accurate to stick it post intercooler to account for turbo heating & IC cooling? looking at the VPC instructions, they replace the fuel filter w/ the temp probe - seems like air temp is being read in the intake manifold.

why do instructions say turbo inlet and not manifold? what are pro's & con's of each approach?

i would guess it has to matter - the heating & cooling of air doesn't seem like it would be linear (i'm too lazy to research this & forget high-school physics..)


meth injection - i intend to use derek's kit at some point and it seems like people using VPC's have trouble if the temp sensor is too close to the injection point; for this application, it seems essential to have air temp sensor in manifold.


3) How would i read air temp from manifold?
let's assume this is the best approach - how would i do it? or should i just drill a hole immediately in front of the throttle body for the sensors?


thanks,
chuck

I think this has been covered many times before in other threads on the forum? You are correct, the AT sensor is designed to provide the factory ECU with a trim so that it can add or subtract fuel as needed for changes in air temp. The stock sensor is calibrated for temperature swings at the inlet pipe, not the intake manifold, which is why the VPC was so hard to tune sometimes on hot days. The sensor is less likely to become heat soaked in the air inlet pipe, but depends on your intake configuration. I only recommend installing the AT resistor in milder climates where there is not a huge temperature swing from day to day. We use them in Texas and have no issues, the fuel maps are very accurate through different temperature ranges using the resistor. However, if you do want to use the supplied AT sensor and you want to install it in the plenum, remove the same gas filter as the VPC and install it there. Hope this helps.

Jarrett H.

[carendt242]

thanks jarret, i found the thread you were probably alluding to:
http://www.supraforums.com/forum/showthread.php?s=&threadid=186431&highlight=iat

for the resistor idea, what is the typical texas temperature range? looks like it's 40-60 degrees now...

i'm guessing you generally need to re-fine-tune during the summer months?

[Veta]

OK


Only a copy of text:


MAP ECU Facts
Hey Guys, I think you have all missed the point here of EFI tuning 101.

Speed density does NOT require the use of incoming air temperature to generate the proper voltage. Everyone seems to think speed density generates an output based on air temperature and volume, which is WRONG. It takes the same volume of air to make 10 psi regardless of air temperature. True that the density of the incoming air will change slightly by air temp, but the air temp doesn't change that drastically at the intake plenum in a forced induction application. Naturally aspirated applications are more sensitive to air temp, but thats another story. All aftermarket EFI systems on the market are speed density based, and all have a single air temperature correction trim that is normally set to zero or increased slightly at the extremes. This includes Motec, AEM, Haltech, and Autronic. The Supra 2JZGTE ECU already has this temperature correction map built in the ECU programming, and it trims both the amount of fuel AND ignition timing when the air intake temperature gets below 20C and above 50C. In fact one of the items we played with years ago on the ECU was lowering the trim corrections so that the ECU did not play around with the fuel mapping as much. On a forced induction car, the only air temperature that even matters is charge air temperature at the intake plenum itself. We have datalogged this temperature on extremely cold days and extremely hot days, and found no more than a 20 degree difference F once the engine was warmed up. Air under the hood is what we are ingesting here, not outside air in most cases, and it seems to stay pretty constant. Also contrary to what has been stated here, from real world experience you would notice that the actual difference in A/F ratio between a cold day and hot one is not that drastic as it may sound on paper. But, if you need to make some SLIGHT changes to the map when a cold front comes through and drops the temperature from 80 degrees to 20 in one day, you can do that. That is the beauty of a programmable system.

Now, to address the HKS VPC. I know many of the actual HKS engineers, and the only reason HKS produced the VPC with the air temperature sensor built-in was for packaging purposes to sell to the retail masses who could not do anything more than plug something in. HKS was not about to tell the public that they had to cut their stock MAF connector and wire in this HKS air temperature sensor, so they did the air temperature correction through the VPC rather than the ECU. They supplied a 2.2k ohm resistor to lock down the stock ECU at 70 degrees F, and did the air temperature correction through the VPC mapping. It follows the factory trim mapping, only its done that way since HKS could make a complete plug-and-play unit by doing it so. Again, we know this because of the many VPC PROM's we have burned over the years. The HKS VPC is the EXCEPTION not the rule in speed density programming.

Personally, we took a different approach with the MAP ECU because of the many changes in MAF metering over the years since the VPC was developed. When Toyota designed the Supra in 1991-2 they decided to incorporate the air temperature sensor into the hotwire MAF meter since it makes more sense from a packaging sense to perform all incoming air measurements at the same location, and to cover their ass. You see, by measuring the air temperature at the inlet source, there are greater temperature swings and the distance gives the ECU time to react in times of EXTREME change... which would more than likely never happen in the U.S., but when did Toyota not over-engineer something for the Supra LOL. With the MAP ECU, you can either leave the factory MAF Meter in place to record the AT correction, install the supplied sensor in the intake plenum or the air inlet tube, or not use either and lock down the correction with a resistor. The choice is up to the tuner and his/her particular style, and the type of air temperature sensor found on the vehicle. Many newer cars are measuring air temperature in different locations now. Again the beauty of programmable EFI.

Again, air temperature is used as a trim calculation in EFI, not to perform the base fuel calculations. I hope this helps to clear up some of these questions.

Jarrett H.
www.mapecu.com
www.powerhouseracing.com


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[8secsupra]

Originally posted by carendt242
thanks jarret, i found the thread you were probably alluding to:
http://www.supraforums.com/forum/showthread.php?s=&threadid=186431&highlight=iat

for the resistor idea, what is the typical texas temperature range? looks like it's 40-60 degrees now...

i'm guessing you generally need to re-fine-tune during the summer months?

That's it, thanks for posting the link! Texas can vary widely from 40 to 100, but I generally dont drive my car in winter months anynow so I dont need to retune much. If you are driving year round, you might want to fine tune in summer and winter, but the tune will still be close enough to be safe. Thanks!

JH