1990 Ranger engine runs rough and stalls when cold

[John RTC Engine Lab]

The engine idle is rough when cold. Driving with a cold engine stalls at idle sometimes. When hot/warm, it drives fine. I started it cold one morning. It idled roughly for about 15 minutes, and all of a sudden, it smoothed out. It was like a switch turned on. I had installed a new master cylinder prior to this new behavior. I didn't find any vacuum leaks. I'm leaning towards a water temp sensor. Does anyone have similar problems?

I'm new to posting to this site and not sure if I posted this correctly.

John

 

[franklin2]

You can test the sensor. Before you start it up, pull the sensor wiring plug off, and put a meter on resistance and measure the ohms of the sensor.

Say it's close to 70F in the morning before you start it. You should be in the neighbor hood of 37,000 ohms. 86F is 24,000 ohms. Start it up and run it till it runs good and the upper radiator hose is hot. You will have to plug the sensor back in most likely to make it run. Once it's warmed up, it should be close to the thermostat temp or a little above. If you have the stock thermostat in it, that is usually around 192-195F. So figure on the engine being around 200F. 200F is about 2,800 ohms. Lets say you turn the engine off hot, and are messing with the wiring plug and getting ready to do the test. Most engines will rise in temp after running. So 230F is 1.550 ohms.

 

[rusty ol ranger]

Pull the codes.

Generally coolant sensors fail when hot and cause a rich condition when warm.

Not saying thats not it...but id do a bit more checking before tossing parts.

 

[John RTC Engine Lab]

Thanks, guys, for responding.

Franklin, where did you find the resistance/temp values? That's the information I couldn't find.

Rusty,
How does one pull the codes? Where can I find the list of codes?

John

 

[rusty ol ranger]

Thanks, guys, for responding.

Franklin, where did you find the resistance/temp values? That's the information I couldn't find.

Rusty,
How does one pull the codes? Where can I find the list of codes?

John

There are various ways...multimeter, paperclip...eaisest way is to buy a innova EEC IV reader...like 30bucks on amazon or at autozone.

Not sure where the plug is on a 90. Its usually in the back corner of the engine bay by the firewall...google will tell you.

The innova reader also comes with a code book....or you can google "EEC IV 2Digit codes"

 

[franklin2]

Thanks, guys, for responding.

Franklin, where did you find the resistance/temp values? That's the information I couldn't find.

Rusty,
How does one pull the codes? Where can I find the list of codes?

John

From this book.

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