Intake Air Temperature (IAT) Mod

History:  This information was posted numerous times, for numerous reasons.  It is posted here for edification and further justification.

(Note:  This is the cheapest and most beneficial Mod ever devised.  It's simplicity is incredible and if I knew who came up with the idea, I would erect a statue in honor of; and dedicate an entire web-page in homage to; said individual.  As I am unable to determine who came up with the idea, I offer the following in hopes that it was posted for public knowledge.)

What is it???

Theory:  The Intake Air Temperature (IAT) sensor (or Air Charge Temperature [ACT] sensor prior to 1992) is nothing more than an Inverted Thermistor.  It's output is Increasing Resistance for a Lower Temperature (voltage drops w/ temp).  As air temperature decreases, the risk of detonation (spark knock or pinging) also decreases.  Therefore, a more aggressive timing curve can be used without risk of detonation.  It also tells the computer that the inbound air is more dense and the ECU adds more fuel (Gasoline or E85) to the mix (A/F Ratio is enriched).

Air-Fuel Ratio Lesson:  The relationship between thermal efficiency, air-fuel ratio, and power is complex.  Without oversimplifying, "Stoichiometric Combustion" (air-fuel ratio = 14.7:1 for a typical non-oxygenated gasoline and 10:1 for E85) is neither maximum power - which occurs with a Rich mixture (12-13 parts Air to 1 part Gasoline, 8 or 9:1 E85), nor maximum thermal efficiency (AKA: Economy) - which occurs with a Lean mixture (16-18 parts Air to 1 part Gasoline, 12 or more for E85).  The air-fuel ratio is controlled at part throttle by a closed loop system using the oxygen sensor(s) in the exhaust.  Conventionally, enrichment for maximum power air-fuel ratio is used during full throttle operation to reduce knocking while providing better driveability.

Oxygenated Fuels:  To reduce "Green House Gases" and smog, the EPA has ordered some areas to use MtBE (Methyl-tertiary-Butyl-Ether) to oxygenate fuels during the winter months.  MtBE is recognized by the State of California as a carcinogen.  Up until September of 2000, you could find articles about this all over the Internet.   What happened?   Before I start on one of my rants, I'll just say that it creates a Lean mixture when burned.  If you are using it on warm days, it can cause detonation.

Note:  Detonation is serious, it is a result of excessive load on an engine that is being fed: insufficient octane; hot air; oxygenated fuels; or has too much initial timing (advance).  Left unchecked, detonation can lead to "Pre-Ignition". This is the point where the fuel "Auto-Ignites" (fuel burns on it's own, before spark is added.   This happens before TDC, creating EXTREME cylinder pressures) during compression and leads to serious damage...

O.K., What Do I Do With It??

Application: By adding resistance to the IAT sensor wiring (inline, like a fuse, on either wire), we can "lie" to the ECU and make it believe the incoming air is (much) colder than it actually is.



or you can do it this way (by HemiOn20s)...At first I used a 6.8K resistor which worked very well, just cut one of the wires on the IAT sensor and just put the resistor in-between the cut wire... then I took that out and made a 0-10K adjustable [in the cab] one so I could have it set at 0[no added resistance] for cool days + winter, or up to 10K for hot weather [around 5-7K works best]. no check engine lights to worry about, and you notice the added power instantly.  (Similar item can be found at Hurricane Nice idea using a "valet" switch to revert completely to stock at a flick of the switch)

DTW forum topic on the mod:

Do a Google search for "IAT mod" ..there you can get all the extraneous info you want on the mod