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Re: 86 9K - test ECU temp sensor? Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 6 Apr 2006 05:37:42
In Reply to: 86 9K - test ECU temp sensor?, wolf_walker, Wed, 5 Apr 2006 17:11:51 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The temperature sensor is a NTC (Negative temperature Coefficient) device. What that means is that it looks like a resistor, and the resistance drops as the temperature increases. It is an infintely variable device - even very small changes in temp will show up as a change in resistance. That said, the ECU doesn't use the signal that way. It makes decisions on fuel flow based on temperature 'bands'. Basically, is the engine cool, warming up, or hot.
The resistance from the LH manual is only provided at three points-
At 0C (32F) it should be 5800 ohms +/- 10%
At 20C (68F) it should be 2600 +/- 7%
At 80C (176F) it should be 320 +/- 5%
As you can see it isn't linear. There is an equation to determine the resistance at any temperature, but it's not necessary.
If you want to really test it, you can pull the sensor out. Dump some ice into some water in a glass, and give it 5 minutes to stabilize. That should be pretty close to 32F (Ice can be much colder from the freezer). Put the tip of the sensor in and measure the resistance. Then pull it out and see how it looks once it warms up to room temp (around 68-70F, typically). If you're real ambitious, you could heat up some water and check the temperature with a candy thermometer.
Or, with the sensor in the engine, let the car sit overnight, and see what the sensor reads first thing in the morning. The block will be about outside temp.
Most likely a bad sensor won't be off a few degrees - a bad sensor will be totally whacked, with wrong readings at all temps.
posted by 192.249....
, Thu, 6 Apr 2006 05:37:42 <-- Viewing This Message, Thu, 6 Apr 2006 11:02:38, Fri, 7 Apr 2006 05:53:15, Fri, 7 Apr 2006 13:48:00
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