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Old 09-03-2014, 07:46 PM   #1
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Default Insanely high MAT's

Hi !, Newb here, just getting to grips with some tuning now. Today I noticed my MAT temps are ranging from 185F to 250F on an 80 deg day here in MI....I have a GM Open element IAT with the following calibration settings....

bias resistor setting of 2490 Ohms.

Temperature F Resistance In Ohms
48 7000
87 1930
146 560

I have attached a log of my run to work which didn't get quite as hot, but still pretty high, any thoughts as to why I've got such crazy high temps - I'm not even boosted....

Thanks for any suggestions and help !
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File Type: msl 2014-09-03_06.49.30.msl (1.57 MB, 49 views)
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Old 09-03-2014, 07:48 PM   #2
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If you have a hot side air intake, the readings are probably accurate.
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Old 09-03-2014, 08:07 PM   #3
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What is your intake like and where is the IAT located?
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Old 09-03-2014, 09:39 PM   #4
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What is your intake like and where is the IAT located?
Sorry about the crappy picture....IAT near the throttle body, intake on the hot side...

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Old 09-03-2014, 09:43 PM   #5
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Are you in a position where you can leave the hood open all night? (garage?)

If so, check your MATs before you start the car in the morning. If it is within a few degrees of what the weather channel says it is then it's probably accurate.

I have never seen MAT that high but then I went from stock airbox to intercooled turbo.
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Old 09-03-2014, 09:46 PM   #6
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Originally Posted by Chiburbian View Post
Are you in a position where you can leave the hood open all night? (garage?)

If so, check your MATs before you start the car in the morning. If it is within a few degrees of what the weather channel says it is then it's probably accurate.

I have never seen MAT that high but then I went from stock airbox to intercooled turbo.
Good idea, i'll try that tonight...
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Old 09-03-2014, 09:50 PM   #7
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FWIW. My MAT's are always 5-10F higher than ambient before i coldstart my car. No matter if it's 30f out or 90f out.
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Old 09-03-2014, 09:53 PM   #8
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well, that's in my realm of "reasonable." If it is more than 15 degrees off or more then I would be concerned.
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Old 09-03-2014, 10:18 PM   #9
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So you're pulling air from right next to the header, and you've removed the heatshield?
It's hot under the hood. You need to work on a cold air intake. The sensor is likely fine.
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Old 09-04-2014, 07:39 AM   #10
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Quote:
Originally Posted by Chiburbian View Post
Are you in a position where you can leave the hood open all night? (garage?)

If so, check your MATs before you start the car in the morning. If it is within a few degrees of what the weather channel says it is then it's probably accurate.

I have never seen MAT that high but then I went from stock airbox to intercooled turbo.
OK, so I left the hood open all night, ambient air temps were around 65F this am, before cranking I checked the MAT - 151F ! - sooo looks like my sensor is bad....The good news is that on my drive into work the MAT only got to 180F, so not too bad a heat rise on this cooler AM. Agree some form of Cold air intake would be a good idea, but based on this my sensor is bad....Can I re calibrate it (Was thinking hair drier and a meat thermometer !) or not worth it ?
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Old 09-04-2014, 09:11 AM   #11
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I've had my intake temps read crazy when it was just a bad connection to the sensor. Disconnect/reconnect the plug on the sensor and see if it makes a difference, if not do the same where it connects to the maf harness. If it's still giving you problems a new sensor is $20: GM Open Element IAT Sensor with Connector DIYAutoTune.com

I've run several logs with a similar intake setup (except with the heat shield on) and temps were hanging around 140-150. That's definitely not an ideal setup, especially with the heatshield off.
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Old 09-04-2014, 12:43 PM   #12
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Have your MATs ever been good? It's possible you put the wrong bias resistor in place?
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Old 09-04-2014, 02:38 PM   #13
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Quote:
Originally Posted by Chiburbian View Post
Have your MATs ever been good? It's possible you put the wrong bias resistor in place?
Thankyou for the opportunity to reveal my noobness ! ;o)

- Is the bias resistor a part of the sensor, part of the MS3x circuit or a resistor I should have soldered into the harness ?
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Old 09-04-2014, 02:46 PM   #14
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It is a resistor that would have been soldered onto the megasquirt board. I believe R7 and R4 are the resistors for coolant and air temperature. Which one is which I am not sure.

Are you sharing your sensors with the stock ecu or running full standalone?

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Old 09-05-2014, 01:01 PM   #15
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Wow, thanks !

Thanks for the post - I'm full standalone

So last night a bought a new sensor, clipped it in, no difference - same high temps. Then I got out my wife's trusty meat thermometer (it's a good one with electric probe, don't tell her) and the hairdryer - and started tweaking some of the resistances in the hope I could set something near to 80F and something around 230ish. after a few tweaks things started to go weird - the gauge stuck on 70F no matter what resistance values were entered. I unplugged the sensor and it jumped between 0 and 70, a few seconds on each - whoa - what the heck is going on !? Then I plugged the sensor back in and temps went to a few degrees above ambient.....go figure. After a brief drive I saw temps rising and falling in expected ranges and it appears to be reading something near sane temps. So for now it appears to be working, but I'll keep a close eye on it and if you asked me what I did I'm not sure I could tell you the route cause or remedy....eeek
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Old 09-05-2014, 01:03 PM   #16
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While it's nice to have everything working, sometimes the unknown "fixes" are the worst because you don't know how to fix it in the future. Perhaps it is a bad wire somewhere?
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Old 09-05-2014, 01:24 PM   #17
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Quote:
Originally Posted by Chiburbian View Post
While it's nice to have everything working, sometimes the unknown "fixes" are the worst because you don't know how to fix it in the future. Perhaps it is a bad wire somewhere?
Yes...I know...I may run new wires just in case....

Thanks for your help anyway !
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Old 09-05-2014, 04:47 PM   #18
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Maybe I'm just dumb, but I couldn't ever get a good connection using the crimps that came with the DIYautotune connector.

I have a disease that makes me own 12 S10's and Blazers, so I just stole and soldered in a GM pigtail. Any 98-04 S10 pigtail should fit.
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Old 09-13-2014, 10:30 PM   #19
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Quote:
Originally Posted by deezums View Post
Maybe I'm just dumb, but I couldn't ever get a good connection using the crimps that came with the DIYautotune connector.

I have a disease that makes me own 12 S10's and Blazers, so I just stole and soldered in a GM pigtail. Any 98-04 S10 pigtail should fit.
That is some disease... I inherited a decent S10 Blazer from my Uncle. Spent quite a chuck of change fixing the AC, front suspension, etc... I still hated the Damn thing and traded it in when buying a GTI. I probably lost $1500+ trading it in and was still happy to see it go!

Anyways, back to vehicles that don't suck... (sorry, no offense meant!)
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