SPDSTR 7

What is the purpose of this? Does it hook up to a gauge?

HAILERS

It's supposed to have a two socket plug connected to it. It gives info to the ECU for fuel delivery. If disconnecte the ECU defaults to a set value for the air intake temp sensor. The one on the intake? Right? Not talking about the one inside the afm. Yeah.

SPDSTR 7

yes it's the one on the TII's TB elbow or the one on the dynamic chamber on N/As. BTW, what is the default value? And what is the relationship of the air temp to fuel delivery? I thought fuel delivery is only affected by air volume

SnowmanSteiner

Is it a really important component or not? And can they be swapped from an N/A to a TII. I don't think mine was orginally connected but after breaking it, I took one off an N/A.

- Steiner

NZConvertible

Air intake temp is a very important input. Air density drops as temperature rises so it is critical the ECU knows the temp of the air entering the engine so it can calculate the correct amount of fuel required. This is particularly important for turbo'd engines, where the intake temp can get very high even with an intercooler. It's also common for the ECU to retard ingnition as intakes temps rise, to avoid detonation.

Project84

Yeah, the colder the air, the dense it is. That means more fuel is needed to burn all the oxygen and maintain the proper air/fuel mixture.

I believe the default temp is 68*F but I can't remember 100% It is an important feature, but it isn't the only part that the ECU looks at for determining fuel delivery. The MAP sensor (Manifold Absolute Pressure) tells barometric pressure. On RX-7s its called the boost sensor, even on the N/As. Coolant temp is also important. So cars don't have intake air temp sensors, they go strictly by the coolant temp.

Project84

Yeah, the colder the air, the dense it is. That means more fuel is needed to burn all the oxygen and maintain the proper air/fuel mixture.

I believe the default temp is 68*F but I can't remember 100% It is an important feature, but it isn't the only part that the ECU looks at for determining fuel delivery. The MAP sensor (Manifold Absolute Pressure) tells barometric pressure. On RX-7s its called the boost sensor, even on the N/As. Coolant temp is also important. So cars don't have intake air temp sensors, they go strictly by the coolant temp.

NZConvertible

The MAP sensor, as it's name implies, measures manifold pressure, not barometric (atmospheric) pressure. The ECU uses a seperate atmospheric pressure sensor inside the car.
They've got "pressure sensor" written on the top of them, and that's what they're called in the manual.

Project84

You are correct, unless the sensor is left open atmosphere. I don't know how every vehicle uses it, but its an optional setup for the Haltech depending on engine config. But yeah, the M in MAP is for manifold, so thus its not barometric pressure.

HAILERS

(******They've got "pressure sensor" written on the top of them, and that's what they're called in the manual. *******

Nay, nay Kiwi! The Factory Service Manual refers to that object as a Boost sensor in the non-turbo section and as a Pressure Sensor in the Turbo section of the manual. See page 4A-31 and page 4B-32.

And the default temp for both air intake temp sensors is 68 * F or 20*C.

And the turbo and non-turbo sensors are the same item on the dynamic chamber or the elbow, whichever is the case.

EDIT: Oh. 1987 FSM

SPDSTR 7

So, if fuel delivery is calculated by air intake temp, coolant temp or boost sensor/pressure sensor, how does the ECU know the exact measurement? Does it do it by averaging?

Aaron Cake

iTrader: (1)

You're forgetting the AFM. The ECU knows exactly how much air is going into the engine via the AFM reading.

Fingers

Is it possible for this sensor to be bad, yet not trip a code in the ECU?

What sort of results would occur if it was off?

SPDSTR 7

yeah, but doesn't the air going into the engine changes after the turbo? now i'm starting to think what the AFM really does if you have a turbo.

Aaron Cake

iTrader: (1)

Yes. If it is slow to respond, yet still produces resistance values in the stock range then the ECU will not produce a code. It would cause A/F ratios to be too rich or lean. Probably effects timing as well.

The AFM tells the ECU how much air is going into the engine. The temp sensor tells the ECU the temperature of that air so it can compensate.

HAILERS

Don't forget the temp sensor in the afm.

Using a Fluke52II, I saw 238 degrees at the INLET to the intercooler this day. And the outside air temp is but 75 degrees. I don't wanna know what the temp is when a normal 100 degree outside air temp is. I might never boost again.

That was on a virtually stock series four putting out 6.5 psi. Someday I'll look at the other car that runs approx ten psi.

When I get my extension leads made up for the other probe I'll see how much the stock intercooler drops the temperature from inlet to outlet.

NZConvertible

How typically Mazda. I stand corrected.
I'm pretty sure the temp sensor in the AFM is used independantly of the one in the manifold or TB. It's only used by the ECU to convert the AFM's volume flow measurement into a mass flow measurement, since the flow and temp must be measured at the same point. But the ECU's final correction for air temp needs to be done from a reading at the TB/manifold, since it takes into account the turbo and intercoolers's effect on Turbos and any heat-soak on NA's.

SPDSTR 7

ok, i did some searching on some stuff and came across a topic about moving the AFM after the turbo or before the TB. How does this affect the ECU's measurements?

NZConvertible

It makes the AFM read less air than it would in the stock location, due to the air being being pressurised. You need a fuel computer to correct the error.