When in open loop....

[Thieaux]

Guys a techical question, When in open loop, does the car only use a predetermine a/f map, spark, fuel and air, or theres something else involve?

Cause i can rev pass 4000 rpm , and im getting code 24 , does the iat work on open loop or just in close loop , cause i might be getting a wron signal and making my car too rich..

 

[superlex1]

ok first things first, the computer runs only in closed loop during cruise and idle conditions. You could have a faultly fuel pump ecu, it can be tested by by-passing it using a bent steel paper clip & bridging the Fp & B+ terminals of the engine diagnostic port. This will make the fuel pump run at full capacity all the time - no safety off when the car stalls or crashes, no half speed when you are cruising - so best to bite the bullet and replace it if it is faulty.

 

[Toysrme]

IAT works all the time & provides a minor correction factor to the ECU. Tho you would think it is important because you need it to accurately derrive the MASS of the incoming airflow - it honestly has little control over the fuel calculations.

If it's dead, you can buy a little $1 thermistor at radioshack & replace it. It's a little harder with an AFM, but not possible. For that matter, if you don't mind the ECU thinking it's 68*F all the time, you could take the regulated 5v power feed AKA VC (sent from the ECU that powers the AFM/MAF/whatever your engine uses), put a 2.5K ohm resistor on the line & feed THAT to the ECU to replace the THA signal.
(THA = name for the IAT signal)

In an AFM it's a little thermistor hanging down on the front of the housing:


On a MAF, they're generally on the side:


Most of Toyota's IAT's have a THA (That's the IAT signal) (I'm interpolating off a chart, but that should be accurate) resistance of:
Temp = middle of spec on chart = plublished TOK range
32*F = 4K ohm = 4-7k omh
68*F = 2.5k ohm = 2-3k ohm
104*F = 1k ohm = 0.9-1.3k ohm
Regardless of AFM, or MAF. They're both the same thing.
My 3vz-fe's IAT sensor in the AFM housing currently (This second) reads:
2.71k ohm @ 70*F. Pretty dang close LoL!





What you need to do tomorrow morning before you crank the car is: Take a thermometer outside & record the temp. Take your MAF/AFM connector off & check the resistance of the THA signal VS the E2 ground.
I can't help you with the pin-outs - you'll need someone else to tell you that.

Anywho... That's how you test the IAT.

 

[Thieaux]

Great info bro , thanks a lot , u da man!!!!

 

[Nick M]

Guys a techical question, When in open loop, does the car only use a predetermine a/f map, spark, fuel and air, or theres something

Yes, closed loop is technically the computer responding its own control. Open loop is not. That is the basic function. Corrections are made to the oxygen content of the exhaust, in addition to the other engine sensors.

And just for some more info, because that is alwyas good, THA= thermal air. What he was talking about if you dont know is the signal to the computer that tells the intake charge temperature, or IAT from just about everybody else.