Correct Resistance range for ECT?
Thread Starter
Heel & Toe
Joined: Sep 2005
Posts: 19
Likes: 0
From: Everett Wa
Correct Resistance range for ECT?
I am still battling the High Idle issue, everything else checks out so far....
I just pulled my Engine Coolant Temp. Sensor and Ohmed it out, (in the meters' 200K range).
Readings started at 4.3 at a sensor temp of about 55 degrees and dropped smoothly to less than 1.0 as I heated it past 150 degrees,
Does anybody know the proper OHM resistance value for the sensor, the manual I have lacks this info.
(1991 Vette 5.7L stock VIN 8 engine)
I just pulled my Engine Coolant Temp. Sensor and Ohmed it out, (in the meters' 200K range).
Readings started at 4.3 at a sensor temp of about 55 degrees and dropped smoothly to less than 1.0 as I heated it past 150 degrees,
Does anybody know the proper OHM resistance value for the sensor, the manual I have lacks this info.
(1991 Vette 5.7L stock VIN 8 engine)
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
All GM says is:
100,000 ohm at -40F
70 ohm at 266F
Powered by 5-volt signal.
It's the same as the MAT sensor that goes into the bottom of the plenum, if you want to compare the two.
100,000 ohm at -40F
70 ohm at 266F
Powered by 5-volt signal.
It's the same as the MAT sensor that goes into the bottom of the plenum, if you want to compare the two.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Or you can spend 9 Bucks on a new one and compare it's resistance to the one installed in your car (cold) - they should be close. Better yet, get a scanner and see what the ECM is seeing. That will also help you to narrow down your idle issue.
Thread Starter
Heel & Toe
Joined: Sep 2005
Posts: 19
Likes: 0
From: Everett Wa
OK...
New ECT installed with lower Resistance values, now... (Something I didn't notice before) Both of my Cooling fans come on at once! I am getting somewhere......
Idle is still high despite resetting the system.
New ECT installed with lower Resistance values, now... (Something I didn't notice before) Both of my Cooling fans come on at once! I am getting somewhere......
Idle is still high despite resetting the system.
Race Director
Joined: Sep 2000
Posts: 17,298
Likes: 33
From: The Top of Utah
Originally Posted by tbu61
Does anybody know the proper OHM resistance value for the sensor, the manual I have lacks this info.
Temp °F....°C........Ohms
....210......100........185
....180.......70........450
....100.......38.......1600
.....70........20......3400
.....40........-4......7500
.....20........-7.....13500
......0.......-18.....25000
...-40.......-40...100700
Obviously the ECM is sensing higher temps as evidenced by the fans, but that wasn't causing the high idle. Back to looking for vacuum leaks.
RACE ON!!!
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Make sure the a/c is off.
Check connector and the signal wire (Yellow) for a short to ground, though that should be generating a Check Engine Light. Scan would still show what the ECM is sensing, but assuming the wiring and connector are good, the a/c is off, and no codes, it's obvious that it senses the engine has reached the threshold for fan operation. That's usually a bad ECM. On the other hand, under these circumstances, there shouldn't be a fast idle even with the engine cold.
Check connector and the signal wire (Yellow) for a short to ground, though that should be generating a Check Engine Light. Scan would still show what the ECM is sensing, but assuming the wiring and connector are good, the a/c is off, and no codes, it's obvious that it senses the engine has reached the threshold for fan operation. That's usually a bad ECM. On the other hand, under these circumstances, there shouldn't be a fast idle even with the engine cold.
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Thread Starter
Heel & Toe
Joined: Sep 2005
Posts: 19
Likes: 0
From: Everett Wa
Finally got the idle to lower to 750-800, took about 4 attempts at resetting.
Now it has a little surge, but I think I have the situation in hand.
Looked for Vacuum leaks and found one tube disconnected already.
Going to make another round with the propane this evening. Maybe get lucky....
Thanks for all the pointers!
Now it has a little surge, but I think I have the situation in hand.
Looked for Vacuum leaks and found one tube disconnected already.
Going to make another round with the propane this evening. Maybe get lucky....
Thanks for all the pointers!
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
I wouldn't short the a/c pressure switch on this Year. It's a thermistor and that will send a 5 volt (doomsday signal) to the ECM. Yes, the fans will run, but your a/c will shut down.
Below 90 - the fan switch is simply and on/off device. When closed, the ECM sees 0 volts on the signal line and that means the pressure is too low for fan operation. Open or disconnected, the ECM sees battery voltage (or whatever the signal voltage is) and it grounds the Main Fan Relay - so disconnecting it turns on the fan.
Below 90 - the fan switch is simply and on/off device. When closed, the ECM sees 0 volts on the signal line and that means the pressure is too low for fan operation. Open or disconnected, the ECM sees battery voltage (or whatever the signal voltage is) and it grounds the Main Fan Relay - so disconnecting it turns on the fan.