Rick's Free Auto Repair Advice

Hard starting and stalling, bad gas mileage

What causes Hard starting, stalling, and  poor gas mileage

There are many things that can cause hard starting and stalling poor gas mileage, but the key to solving this particular puzzle is the clue about poor gas mileage. One inexpensive sensor can be the cause of all these problems—the engine coolant temperature sensor (ECT).

When you turn the key, the computer takes a quick look at the ambient air temperature

ECT, engine coolant temperature sensor, IAT, MAF, MAP

Typical engine coolant temperature sensor (ECT)

and the ECT. By comparing the two temperature readings the computer knows whether the engine is cold or at operating temperature, and whether it’s hot or cold outside. Based on those two readings, it decides what the air/fuel mixture should be.

A cold engine needs a rich mixture to start and stay running. As the engine warms, the sensor reports the warmer reading to the computer and it leans out the mixture. However, if the ECT isn’t working properly, the computer will continue to pour fuel into the engine. That’s where you get poor gas mileage.

The ECT is a thermistor that changes resistance based on temperature. To test it, you’ll need an ohm meter and a reference chart. Car makers usually install two coolant temperature sensors—one for the instrument panel gauge and one for the engine computer. Make sure you test the right one. ECT sensors usually cost less than $25 and are easy to install. If you’ve neglected changing the coolant in your vehicle, your ECT could be corroded or coated with insulating deposits.


© 2012 Rick Muscoplat


Posted on by Rick Muscoplat

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