Rick's Free Auto Repair Advice

Hard starting and stalling, bad gas mileage

Hard starting and stalling 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.

For more information on this repair or any others for your vehicle, buy an online subscription to either Alldatadiy.com or eautorepair.net. Click on this link to compare the two services: Compare Alldata and Eautorepair.

You need a professional shop manual to work on a late model vehicle. And you need access to the latest technical service bulletins so you don’t waste time and money replacing parts that may misbehave due to a manufacturer’s software glitch. Forget about those cheap manuals you find at the auto parts store. They will just lead you astray. Here are the two best online shop manuals around.

Eautorepair.net is really Mitchell On Demand with a consumer style interface.
Get a 1-Month subscription (31 Days) for $16.99, 1-Year (Best Value!) for $25.99, or a    4-Year (Best Value!) for $39.99. I like the wiring diagrams in Eautorepair.net better than the hard-to-read factory diagrams on Alldatadiy. However, Eautorepair.net doesn’t show how to remove trim or door panels. Alldata does.

AlldataDIY.com is simply Alldata with a consumer style interface. They have a different pricing model. But a 1-year subscription for $26.95. Add additional vehicles for $16.95 for a year. Or, buy their 5-year subscription for $44.95. Add additional vehicles for $29.95 for five years.

© 2012 Rick Muscoplat

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Posted on by Rick Muscoplat


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