Moving the ACT and the Impact on the ECU

Lets ask another question about inlet air temp sensors. I have a PMS mass air with 6 pins. Two of which I do not use. I am told these two pins are for ACT sensor wires. I assume the 6 pin mass air is similar to the Lighting mass air. Why then would Ford chose to use the ACT senor in the inlet air tract rather than in the lower manifold?? My guess is that the newer computers can change and process this information better than the Fox computer. Any thoughts.

sweet88gt said:

Lets ask another question about inlet air temp sensors. I have a PMS mass air with 6 pins. Two of which I do not use. I am told these two pins are for ACT sensor wires. I assume the 6 pin mass air is similar to the Lighting mass air. Why then would Ford chose to use the ACT senor in the inlet air tract rather than in the lower manifold?? My guess is that the newer computers can change and process this information better than the Fox computer. Any thoughts.

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MHO is that the inlet tract is more sensitive in regard to measuring *actual* inlet air temps. The caveat is that if something is going on and the air is getting heatsoaked by the time it reaches the chambers, the IAT cannot possibly know this. The lower intake location gives a reading closer to where it matters but I fear it's slower to react to real time air-temp changes (the magnitude of air temp changes isnt generally great anyhow, so maybe that's a moot point).

Glad I could muddy the waters there.

If not already touched upon, the ACT is the Air Charge temperature sensor, aka, IAT (Intake air temperature sensor). I segregate the nomenclature as follows: if the sensor is in the lower intake, it's an ACT. If it's in the inlet tube, it's an IAT.

It really doesnt matter (like other similar acronyms: IAB, IAC or as the RT guys say, ISC).

vristang said:

OK, I have been focusing my thoughts on N/A applications, while you have been focusing on Boost applications.

I have not played with boost yet (and I did say YET), but my understanding is that the higher the boost level the higher the air temp will be.
Considering this, I don't find it hard to believe that your ACT temps are not changing significantly.

I guess I am still not convinced that heat soak is what is causing your high ACT readings. I would guess it to be due to the process of compressing the intake charge. I am sure heat soak does play a factor, I just don't see it contributing ALL of the heat retention you are seeing.

Again, thanks for posting. Your comments have made this a great discussion, as most of this stuff never would have crossed my mind otherwise.



jason

EDIT: WOW, already on the second page...

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Just a bit more information on what I have noticed with my setup.

I previously mentioned that once the engine was heatsoaked, the ACT read a fairly constant 180* during cruise, idle and showed a slight temp decrease during WOT.

With the relocated ACT sensor, early fall temps were in the mid 70's while WOT temps increased into the mid-high 80's. This is what I would expect to see in boosted applications with an intercooler.

The heatsoaking that was occurring was making it extremely difficult to tune with the megasquirt. With the extreme ACT temperature differences between pre-heatsoak and heatsoaked my fueling was getting thrown way off. You can see the megasquirt fueling equation here… http://www.megamanual.com/v22manual/mfuel.htm#equation

Correct me if I'm wrong, but I believe the stock ECU only retards timing based on the ACT readings. It's my understanding that the air density differences between hot and cold is differentiated via the MAF sensor in which the computer then adjusts. I don’t believe that with the stock ECU heatsoak is an issue….as it does not serve quite the same function.

I also don't believe the air dwell time in the lower intake is sufficient to increase temperatures and significant amount…especially the 100*F that I noticed. The only time the air will subject to heat transfer of that magnitude is when the car is shut off for any significant amount of time. I myself have to adjust my startup enrichments based off of engine temp in which I can compensate for this.

Anyways, just some argument and food for thought.