running my scan tool today and noticed my MAT sensor reading started at 150 degrees. thought it seemed odd since it was only 40 degrees outside. unplugged it and the reading went high to over 300 degrees which i expected if the wiring was good. plugged it back in, changed the sensor with another one, layed it over to the side and still the same reading. comes down a little bit while driving but not to where it should be. does the ecu have a default value that it starts at or do i have a problem? same sensor and principle as the coolant sensor and that starts low and goes up. any insight is appreciated.

 

It should be somewhere around 10 - 90 degrees celcius depending on underhood temperatures.

 

If you have a TPI and the MAT sensor in the intake manifold, that's about the right temperature. So much heat is being conducted into the sensor that you're actually reading the temperature of the aluminum manifold rather than the incoming air.

I relocated my sensor into the air duct and now I read just over 100°F on hot days. Underhood temps are going to affect it no matter where you put it.

 

No the sensor is actuall well divorced from reading the manifold temp.. I redid one and inserted a plastic pipe adapter between it and the manifold and it made no difference.

When you change locations to see what you want, you not letting the ecm see what it wants. It's not about letting it see a lower temp., it about correctly compensating for some variable.

Moving sensors around without knowing what they're used for, is just busy work. Letting the ecm *see* the intake charge as close to the combustion chamber is the name of the game.

 

it had been relocated to the elbow in the intake duct work for some time so the manifold temps would have no affect on the reading. if the MAF measures the speed and density of the incoming air then why even have a MAT sensor? what is the ecu using the information for, and how does it affect certain tables? someone posted on another board that it was only used for EGR funtion. is this true? going to stick the sensor in a cup of ice water to see if it goes low.

put it in the ice water and it read 200 degrees F. had extended the pigtail so i thought i might have crossed the wires. switched them around, and the same thing. any other suggestions?

 

Sounds like you need to read up on your application/ecm and see what it's used for. There's alot of hearsay on the Internet.

There is a temp/ohm scale in most any service manual that shows what the resistance should be for a given temp..

 

Would you suggest for me to put the mat back to the manifold? Does the 730 use an air intake temp sensor(instead of mat)?

 

Bad sensor

 

Hmmm... I'll take your word for it, but I'm not sure how that is the case.

Even with the plastic pipe adapter, manifold heat will still be conducted to the sensor, just not as fast as through aluminum, given the tremendous difference in thermal conducitivity.

 

Sounds like the scantool is doing something weird. In ice water it should show somehting like 220/~8 counts/kohms for the raw data and resistance, respectivly. Hot, near the boiling point of water, should be like 30/.2 counts/kohms. These are for the sensor I ahve so yours may vary but it should be soemwhere around there for an RTD.

 

the sensor is brand new. the scan tool reads out in degrees farenheit or celsius. haven't put an ohm meter on it yet to see what the resistance is reading.
did a search and came up with a second time that the MAT is used only for egr function on MAF cars. no ses light and if it doesn't affect my tune, then i'm not gonna worry about it. to many other areas i'm trying to figure out.

 

Tell ya what,
don't believe me, rework you manifold to use phenolic or whatever you thinks a worse conductor, and repeat the experiment.

Might even get the the specs on the sensor's and their response times, to see which one is best, and get one to see if it's needed or if the GM oem is just OK-Fine. Then install what ever you find and see if the faster response times mean diddly.

Easy enough to do, then we'll have verification of what I've found.
Or if your results vary, then there'd be something to discuss.
Please, feel free to actually try the isolator, and see what you find. And if you look at the sensor, you'll see the element is actually out in the air stream, and while there might be a few degrees error from radiated heat, it ain't enough to worry about.

BTW, I can generate +200dF MATs, so this is important to me, and I've done my homework so I don't have to guess, or just take someone's word on the subject.

 

Where was it to begin with?.
What is it used for in the code your running?.

While it's easy to think of the guys at GM as just being some clowns that don't really know much, they're a whole bunch more clever then folks give them credit for (speacking of the engineers not the bean counters that manage to screw things up).

So while it might seem clever to relocate it, if the MAT is used as it is in some codes, then it might also allow for some fudge factor in accounting for fuel temp.. Telling the ecm the fuel is cooler then it actually is, is 180d from what you'd really want to do if your looking for more HP.

But, the best thing to do is actually do some source code were things could actually be accurately done.

 

FYI, I'm talking about the 730 ecm.

I couln't agree more. That is why my fat cammed, HSR 406 still uses closed loop with the iac working.

I used a v6 air intake temp sensor off my 87 v6. I think there is a major design diff between a MAT and "AIT" sensor. One is designed to run close to the air filter(more or less) and the other is liquid or oil filled and is located directly on the intake. To be honest I don't know the difference in the code though. So that is why I asked if I should put the mat back on the intake.

I have tuned my car fairly close(wot is perfect), so do you think I should continue to use the AIT sensor and finish the tune? Like I stated I don't know the difference in the code but they both work in a "similar" fashion. I do know that the v6 ecm will not accept the MAT(throws a code). So there is some difference.



You mentioned something else.
I used the v6 sensor because it seems like a better designed sensor for measuring air intake temps. There is less heat soak(for sure) and it responds quicker to the incoming air. That seems like a good thing. But I did not take into acount stuff like fuel temp.

Doesn't a camaro(w/730) have the air sensor on the intake?

Now you have me confused as to what I should do........

 

Could someone explain how the MAT is related to fuel temp? Thanks

 

Its not, really. The fuel can be pretty much any temp depending on what the conditions are and how hot the walls of the intake runners are. I personally dont see anything wrong with putting the MAT in the intake ducting. After all, its to be used to correct for external conditions. If heat really does conduct to the sensor, then having it in the intake wouldnt make much sense as it is pretty much the same temp as the engine and will remain constant for the most part. Looking at mine, though, the sensor is housed in a plastic casing and the actual RTD is supported by thin leads that really wont conduct heat so its realatively well isolated. After testing it, though, the sensor isnt too accurate and falsely reports the temperature. If i was going to seriously rely on it, I would calibrate the table to the individual sensor to ensure that I got the correct readings, especially at low temps where the response declines.

 

Grumpy, I was hoping that you would reply to my last 2 posts(in this thread)........

 

You need to read thru the hac and see exactly what the IAT/MAT is used for.
Or fire up an ecm bench, and see for sure what it does.

*I* use the pipe threaded, sensor in a cage type, sensor.
And then mount it in the air stream right behide the TB.

And then watch the CTS, MAT and see which is changing and what the AFR/timing is doing.

 

Guess I really need a bench. Maybe I'm just lucky that my 406 has held up to years of crazy table changes. I keep running into brick walls(not knowing assembly). With the bench I can make changes w/o fear. I would buy one this second if I had the cash

 

Some times you gotta sacrifice.
Take Baloney sandwhichs to work for lunch, have tap water instead of a coke, there's a million things you can do to pinch a penny, if your really want to.
I have a total of 4 benchs now. Why?. Just because they are so convient, and save so much aggravation. And you wouldn't beleive how handy it can be to run two ecms side beside at times.

 

I know what you mean. It's just hard cause i can only do so much. I'll have one in the near future FOR SURE! Just a matter of time and money. Most of the questions I have could be hammered out with a bench.

The mat I'm using now is the basket type. The original mat for every TPI I've seem is the solid type filled with a white or gray liquid located under the plunum and above the egr. I would really like to nail my mat tables.

The funny thing is the 302 ecm couldn't function with the tpi style mat. But the 165 and 730 both works fine with a v6 mat. strange......

 

Everything I've read, and sensors I've played with for temps, have had the same resistance vs temp ohm spec..
You sure the ecm isn't smoked?.

 

the 302? nope, it works fine. Since I used the mat off the v6, I had the tpi mat laying there. So I installed the tpi mat on the v6 (for various resons). The v6er wouldn't even start. But once the tpi mat was removed it would fire up.strange stuff.