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I3 GM tune review / Outside Air temperature

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Moderator: mikel


Posts: 5
Is it possible to modify/set the 'outside air temp' to a fixed temp? In other words make the ECM/? think the outside air temp is something other than what it is? I have noticed when air temp is 60-65* I get great MPG, below 48* MPG starts dropping 3-5 mpg. Assume fuel runs richer at low temps, understood, but would like to keep a leaner mix to see what happens. I had a 98 Silverado I put a resistor in air temp connector to run rich, was told ECM now thinks its 38*. Major boost in throttle response.

Diablo I3 MPG 87 tune, DOD/AFM 'enabled', mid shift tune. Noticeable improvements, very improved shift response, throttle response improved, increased 1-2 mpg. AFM was fine, then started switching back n forth 4-8 too frequently, so went back to the I3 and set DOD/AFM disabled. Even better improvement in throttle response and shift performance, increased mpg 2-3 above standard setting. Latest mpg 19-20.
Stock tune was getting 16-16.5 mpg, very sluggish throttle, erratic shifting. 50-60 mile a day city highway mix. Air temp 15-40*.
A 360 mile highway road trip, Air temp 49-51*, 70-85 mph, 17 mpg, stock tune.

First Diablo tune at 2100 mile, AFM disable at 2500 miles, have ran approximately 700 miles since and very impressed with overall performance from the I3.

2018 Silverado 5.3
stock everything, no mods, no bed cover.


Posts: 54709
Location: DiabloSport World Headquarters

No way to edit the outside air temp.
The PCM doesn't really use that, it monitors air temp in the intake tract and adjusts timing/fueling based on that.
Tricking it can lead to decent results in many cases, but it can also lead to terrible things if you get into a situation where IATs are high and the pcm is running timing as if its cold outside...

Glad to hear you are enjoying the tuner :)
Mike Litsch
Powerteq Customer Service Manager
Diablo Tech support by phone:
561-908-0040x4
M-F 8:00 AM to 5:00 PM EST


Posts: 5
mikel wrote:
No way to edit the outside air temp.
The PCM doesn't really use that, it monitors air temp in the intake tract and adjusts timing/fueling based on that.
Tricking it can lead to decent results in many cases, but it can also lead to terrible things if you get into a situation where IATs are high and the pcm is running timing as if its cold outside...

Glad to hear you are enjoying the tuner :)


I'm a newbie to these electronic controlled engines..... so is it possible to set the intake temp to 65*? I dont completely follow IATs high and pcm timing running as cold if actual temp is 90* and intake temp is 65*.....
is it too much to explain in a couple sentences.... as I noted pryer when temp is 65* I get much better mpg, 3-4 mpg more.


Posts: 54709
Location: DiabloSport World Headquarters

No, you cant set intake temp, that value is read buy a sensor under the hood and reported to the pcm so it knows whats going on.
Mike Litsch
Powerteq Customer Service Manager
Diablo Tech support by phone:
561-908-0040x4
M-F 8:00 AM to 5:00 PM EST


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