GM IAT failure? - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


MEGAsquirt A place to collectively sort out this megasquirt gizmo

Reply
 
 
 
LinkBack Thread Tools
Old 01-15-2009, 12:58 AM   #1
Elite Member
Thread Starter
iTrader: (5)
 
akaryrye's Avatar
 
Join Date: Jul 2006
Location: Central California
Posts: 2,526
Total Cats: 0
Default GM IAT failure?

I have been seeing temperatures about 20* higher than expected from my GM IAT. The sensor is wired directly, grounded at ecu ground by the TB and the other going to megasquirt. I am using GM settings and 2490 bias.

Tonight I ohm tested the sensor in boiling water and found that it read around 240 ohm. In Ice water, it reads 7640. According to the chart below, the sensor should be reading closer to 180 and 10500 respectively. The ohmmeter was tested against a 270 ohm resistor to assure that it was functioning correctly. It read 266 for all 3 resistors tested, which is within the 5% tolerance spec.

Aside from being almost exactly 20* off, the sensor seems to act normally, so can I simply use these numbers ive gathered, and adjust adjust the temperature I input to easytherm by about 20* for the middle one?

example:
212 -> 240ohm

32 -> 7640ohm

... wait as i am doing this, it is seeming more complicated. the curve has been thrown off and it is not 20* off everywhere, its about 8* off at 32 and 20* off at boiling... help me get that middle value right someone, my math sucks
Attached Thumbnails
GM IAT failure?-gm-sensor-bias.jpg  

Last edited by akaryrye; 01-15-2009 at 01:03 AM. Reason: gm temperature sensor bias
akaryrye is offline   Reply With Quote
Old 01-15-2009, 01:05 AM   #2
Elite Member
iTrader: (15)
 
patsmx5's Avatar
 
Join Date: Aug 2007
Location: Houston, TX
Posts: 8,796
Total Cats: 248
Default

A new sensor is cheap. Is it open or closed element? Closed element ones are everywhere.
patsmx5 is offline   Reply With Quote
Old 01-15-2009, 01:07 AM   #3
Elite Member
Thread Starter
iTrader: (5)
 
akaryrye's Avatar
 
Join Date: Jul 2006
Location: Central California
Posts: 2,526
Total Cats: 0
Default

open element
akaryrye is offline   Reply With Quote
Old 01-15-2009, 01:13 AM   #4
Junior Member
iTrader: (2)
 
Join Date: Nov 2006
Location: N/A
Posts: 360
Total Cats: 0
Default

Just leave it....it doesnt have to be exact, just consistent.
mikeflys1 is offline   Reply With Quote
Old 01-15-2009, 01:24 AM   #5
Elite Member
Thread Starter
iTrader: (5)
 
akaryrye's Avatar
 
Join Date: Jul 2006
Location: Central California
Posts: 2,526
Total Cats: 0
Default

it matters to me, I want accurate temps
akaryrye is offline   Reply With Quote
Old 01-15-2009, 01:55 AM   #6
Elite Member
Thread Starter
iTrader: (5)
 
akaryrye's Avatar
 
Join Date: Jul 2006
Location: Central California
Posts: 2,526
Total Cats: 0
Default

Ok well according to some calculations I made, the curves would probably cross at around 37*C

Basically I discovered that the stock resistance at 0*C is 11550, and that my sensor is reading 66% below this. Then I figured that at boiling, my sensor is reading 77% higher OHMs.

66/0C x 177/100C = 37.3*C ... i know my math is probably screwed up, but the number seems to be about where it should be. So my easytherm settings will be as follows:

0C - 7640
38C - 1800
100C - 240
bias - 2940

This should get me a lot closer than it is reading now at least.
akaryrye is offline   Reply With Quote
Old 01-15-2009, 03:04 AM   #7
Elite Member
Thread Starter
iTrader: (5)
 
akaryrye's Avatar
 
Join Date: Jul 2006
Location: Central California
Posts: 2,526
Total Cats: 0
Default

and it is working, looks to be reading within a degree or two from what I can tell.
akaryrye is offline   Reply With Quote
Old 01-15-2009, 05:03 AM   #8
Supporting Vendor
iTrader: (10)
 
Reverant's Avatar
 
Join Date: Jun 2006
Location: Athens, Greece
Posts: 5,440
Total Cats: 198
Default

Inspect your Easytherm output files after you are done. Easytherm really screws up if your vales are off by a degree, and it doesn't even tell you that something is wrong.

Jim
Reverant is offline   Reply With Quote
Old 01-15-2009, 11:58 AM   #9
Elite Member
Thread Starter
iTrader: (5)
 
akaryrye's Avatar
 
Join Date: Jul 2006
Location: Central California
Posts: 2,526
Total Cats: 0
Default

Quote:
Originally Posted by Reverant View Post
Inspect your Easytherm output files after you are done. Easytherm really screws up if your vales are off by a degree, and it doesn't even tell you that something is wrong.

Jim
I dont understand what you mean by this, I thought easytherm simply took the temperature vs resistance curve and scaled it out?
akaryrye is offline   Reply With Quote
Old 01-15-2009, 12:41 PM   #10
Supporting Vendor
iTrader: (10)
 
Reverant's Avatar
 
Join Date: Jun 2006
Location: Athens, Greece
Posts: 5,440
Total Cats: 198
Default

Easytherm CREATES the T vs R curve from the values you give it. If the values you give it are off by a degree or two, the output will be TOTALLY wrong, like random garbage, not just scaled out with less accuracy.

Jim
Reverant is offline   Reply With Quote
Old 01-15-2009, 08:04 PM   #11
Elite Member
Thread Starter
iTrader: (5)
 
akaryrye's Avatar
 
Join Date: Jul 2006
Location: Central California
Posts: 2,526
Total Cats: 0
Default

ok ill take a look at it.
akaryrye is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Expected intake temps on the track? tazswing Race Prep 20 10-03-2015 12:04 PM
Bad head gasket or ? shooterschmidty Engine Performance 8 09-30-2015 11:28 PM
Missing/knock at idle, can someone point me in the right direction? Mikel MEGAsquirt 4 09-28-2015 05:46 PM
IAT on MS3 gsyk59 MEGAsquirt 2 09-20-2015 05:54 PM
ME221 Now has Autotune and Long Term Fuel Trim Tables Motorsport-Electronics ECUs and Tuning 0 09-05-2015 09:02 AM


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 05:25 AM.