Air Temperature

[Calan]

Just made some runs, and on my loggers (MMCd and PocketLogger), my air temp reading never varies from either 79.7* or 80.5*... ever. Outside ambient temperature is currently around 35*.

1. Where is this reading taken from?

2. Does the GM Maf and MAF-T not send this to the ECU?

3. If this is abnormal, what could cause it?

I'm having all kinds of knock/tuning issues at the moment and wondering if this is part of my problem.

Thanks

 

[JayRolla]

I dont think the gm maf have a temp sensor, thats what makes tuning harder. But then others told me they do so im confused after reading what you just posted.

 

[dcg9381]

Just made some runs, and on my loggers (MMCd and PocketLogger), my air temp reading never varies from either 79.7* or 80.5*... ever. Outside ambient temperature is currently around 35*.

1. Where is this reading taken from?

2. Does the GM Maf and MAF-T not send this to the ECU?

3. If this is abnormal, what could cause it?

I'm having all kinds of knock/tuning issues at the moment and wondering if this is part of my problem.

Thanks

1) I don't know the DSM that well, but there is probably an IAT sensor in the intake system somewhere.

2) MAF is manifold absolute pressure, seperate sensor.

3) Not abnormal. I do megasquirt on other cars, turbo and not turbo. For an NA application, I regularly see 30-40 degrees above ambient temp (70) in the intake system - this is why a cold air intake works so well. It really depends on where the air is being pulled from. On a turbo car, 70 degrees outside, under light boost 125-145 degrees.


timing issue?

 

[Calan]

...

3) Not abnormal. I do megasquirt on other cars, turbo and not turbo. For an NA application, I regularly see 30-40 degrees above ambient temp (70) in the intake system - this is why a cold air intake works so well. It really depends on where the air is being pulled from. On a turbo car, 70 degrees outside, under light boost 125-145 degrees.

What has me wondering is that it always reads one of these EXACT two values (79.7 or 80.5)... not something in between. It just switches between these two randomly, so I'm guessing this is either a default value for no sensor being supplied to the ECU, or something is FUBAR.

What I was asking about the GM MAS and MAFT was whether or not this combination is designed to send the temp signal to the ECU.

FWIW, I do see the Barometer reading varying a little, usually between 14.31 and 14.5

 

[Mitchel63]

Our intake temp readings are taken in the MAS. The GM unit does not have this feature so you will log a constant temperature all the time.

 

[antlip]

Our intake temp readings are taken in the MAS. The GM unit does not have this feature so you will log a constant temperature all the time.

Thats exactly what I was told.

 

[BISHILVR]

Our intake temp readings are taken in the MAS. The GM unit does not have this feature so you will log a constant temperature all the time.

This is true, as the maft holds the temp sensor input at a constant. The GM maf uses intake air temp, but does'nt output it, instead it extropolates the baro and flow readings using it.

 

[Calan]

So how does this constant temp affect the ECU and tuning?

 

[BISHILVR]

It does'nt much really, it just keeps the temp signal locked to keep the ecu happy, and then it is one less variable for the maft to deal with. That can be good AND bad, as the car will sometimes run crappy in cold weather if you had it tuned just right in the warm weather since there is no temperature compensation anymore. For some tuners like myself, the temperature compensation wont matter because I dont drive my tuned car in the winter months anyway. For others you might have to make a few changes after any major change in outside temperature if you dont like to let the car warm up before you drive it, and even then if its a drastic temperature change say it was tuned when it was 70* outside and now its 20* then it probably will not respond as well until you re-tune the air fuel for the colder/warmer temperatures. Thats just the trade off for using a piggy back tuning system though.

 

[dcg9381]

I use megasquirt.. If you wanted to install a GM sensor somewhere in your intake piping, it's pretty much cake. A decent sensor that has an isolated thermistor runs about $20 and is a standard NPT thread. Diyautotune.com has one.