I was reading in an old Fiero book about some maintenance items and came across something about the MAT sensor.
Mainly, due to the fact that even though not exposed to direct outside elements it does go through cycles all of the time of heat and cold.
The book said that it can start getting weak and losing it`s accuracy without setting a code.
I was just wondering what you guys thought of this.

87&up can you eat the mat because of back fire.
The six has less problems but yes, it could be bad without cause a code.

the mat and other temperature sensors can lie to the ECM before the sensors are totally dead.

see my cave, DIS and 700 TBI in L4 engine section. the DIS article explains how the sensors can lie.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

Indeed, a faulty one can drive your ECU nuts -make it screw up the A.F ratio real bad and not set a error code. On the + side, they're easy to check with an ohm meter and very cheep to replace.

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trueleo.com
RSpiderII@aol.com

Thanks guys.

I just put in a new MAT on my 1988 Duke. My mileage had dropped from the mid 30s to 28 on the last fill. With gas at $4.10 here... I care. Just checked... Back to 35mpg mixed driving. I did disconnect the battery for a while to help the car forget the bad data. The part was $15.

Fiero ECM has no history on any sensor.
If you don't have DTC then Resetting ECM does nothing.

"Learning" takes a few mile when you go "Close loop" operation.
Close Loop mean O2 is hot enough to work and that happens 30sec-2 minutes of run time.

Change sensor = bad MPG then
Bad new sensor
something else broke

Not true. The ECU learns driving behavior and uses all sensor inputs to do so. Cars have gotten a lot better and quicker about “learning” but back in the mid 80’s this was a very noticeable phenomenon to the point where GM published service bulletins about it. Almost always the most noticeable issue is a loss of mileage.

What are the resistance values and temperature coefficients of the MAT sensor?

Does the ECM learn anything other than BLM & IAC-idle speed?

So you could trick the ECM into thinking it's cold out by jumping the terminals with a resistor? Or Dial in your own A/F mix with a variable resistor?

quote Originally posted by PatrickTRoof: So you could trick the ECM into thinking it's cold out by jumping the terminals with a resistor? Or Dial in your own A/F mix with a variable resistor?

That would work while the ECM is in open loop mode. But after it warms up, the O2 sensor takes over.

I think the MAT sensor only triggers a trouble code on an open or shorted circuit. That leaves a lot of leeway for incorrect readings. So it could be reading way off, and still not trigger a trouble code. But it can still make the engine run like crap.

I just fired up my 85 GT for the first time in almost ten years, after installing a stock rebuilt engine. The ONLY code it threw at me (so far) was for the MAT sensor, which wasn't even plugged in at the time!

quote Originally posted by phonedawgz: Does the ECM learn anything other than BLM & IAC-idle speed?

Not to my knowledge.

quote Originally posted by PatrickTRoof: So you could trick the ECM into thinking it's cold out by jumping the terminals with a resistor?

Yes.

quote Or Dial in your own A/F mix with a variable resistor?

As Blacktree explained, no. That's the way most of the scam "power boost" devices sold on eBay are supposed to work ... $20 for a 15-cent resistor. They don't work.

quote The ONLY code it threw at me (so far) was for the MAT sensor, which wasn't even plugged in at the time!

Think about it. Unplugged is the same as a sensor that has failed open. Infinite resistance implies < -40 degrees MAT.

quote Originally posted by PatrickTRoof: So you could trick the ECM into thinking it's cold out by jumping the terminals with a resistor? Or Dial in your own A/F mix with a variable resistor?

ECT and MAT are used in close loop and Can cause DTC 44 and/or 45...
Example, 87 DIS L4 is good for bad MAT causing 45 at idle, often in winter, in close loop.

quote Originally posted by theogre: ECT and MAT are used in close loop and Can cause DTC 44 and/or 45... Example, 87 DIS L4 is good for bad MAT causing 45 at idle, often in winter, in close loop.

Yes, they are used in closed loop mode. But their role in fuelling calculations is greatly diminished compared to open loop mode.

quote Originally posted by Marvin McInnis: Think about it. Unplugged is the same as a sensor that has failed open. Infinite resistance implies < -40 degrees MAT.

I know. I was just saying, only one code isn't bad for a first startup.

I was trying to get mine to idle better and found that dropping the $18 for the new MAT sensor even though there was no code really helped with the shaky idle. so i have to say I agree with that book you read.

-John