CHT Ohms Reading

[chateau]

Hi All, I feel the car is running too rich so Ohm tested the CHT sensor with the engine cold and external temperature about 25c. It is reading 1.99k although the reading should be between 2500 and 3500. Would this be causing the problem?

[76FJ55]

Is it just rich at cold start or when up to operating temperature too? What is the resistance when the engine is up to full operating temp?

Edit: Is the issue throughout the full RPM range or limited to Idle, Cruise, WOT...?

[spuggy]

Why do you think the car is running rich? Smell fuel in the exhaust? Black smoke? Sooty plugs? Sluggish on throttle tip-in? Dying at idle?

This is more likely to be leaking injectors, I think.

Originally Posted by chateau

Ohm tested the CHT sensor with the engine cold and external temperature about 25c. It is reading 1.99k although the reading should be between 2500 and 3500.

You should look again at the response graph for a Bosch NTC thermo sensor. Might see it more clearly in the table; 20C is 2,500 Ohm, 30C is 1,707.

Temperature Sensor NTCÂ M12

The line isn't straight. If it were, the mean of those two values would be 2103. So if anything, your CHT might be reading slightly too low - indicating a higher temperature (and thus backing off on warmup == leaner).

I think it's fairly unlikely this is a problem though.

Originally Posted by chateau

Would this be causing the problem?

Based on tweaking my warmup compensation, I'd say the Motronic is done with anything the CHT says once it reports 60C or so - because the car isn't warming up at that point, it's entirely done.

[chateau]

Hi, Thanks for the replies. I feel it is running rich as there is a strong smell of petrol from the exhaust when fully warmed up. I will get round to measuring the sensor when the engine is hot. I tried disconnecting the sensor with the motor running and it started racing.