Bad temp sensor = hesitation?

[magicmike]

could someone please explain to me how this is related. I did some searching looking for the actual definition of hesitaion and only found posts about people describing all sorts of different stuff and wondring if it was in fact hesitation. So I have two questions.

1. what is hesitation?
2. why do people say to replace your temp sensor when you are experiencing hesitaion?

thanks in advance.

[Legacy777]

My simple definition of hesitation for car related situations is when you press on the gas pedal....the car does not immediately take off. You could probably corrolate hesitation with throttle response.

As for how the coolant temp sensor can affect things is due to the A/F ratio. If you have an excessively rich A/F ratio, response can be sluggish.

[magicmike]

Finally a response! thank you!

ok based on your definition I have hesitation. I'm not really understanding the relationship between the temp sensor and the a/f ratio. I thought that the MAF controlled the a/f ratio? I'm not saying your wrong I'm just asking for some more elaboration please.

[Matt S.]

I can't give you too much info unfortunately, but I do know that on start up, the ECU reads the temp sensor to determine how hot/cold the engine is and adjusts the fuel accordingly. For instance on a cold winter day, the ECU would richen the A/F mixture quite a bit since the car would start/run better with more fuel when very cold. As the temp sensor reads higher temps, the A/F mixture gets closer to normal because the warmer motor no longer needs as much extra fuel.

What Josh is saying, is that if the temp sensor is giving the ECU bad readings(say, too low), and the ECU compensates for this by adding fuel because it thinks the motor is still colder then what it actually is(see above), then you have an over-rich condition which could cause a hesitation/bogging/whatever as Josh said.

I didn't know whether the ECU continues to rely on temp sensor readings while at operating temperature or not though.

And for what it's worth, I remember quite a few years ago a customer at the Sube dealership I worked for needed a temp sensor. We just sold the last one earlier that day. Upon looking at the old sensor, it was all "tarnished", not the nice shiny copper color of a new one, and it had typical old coolant residue all over it. I took it over to the grinding wheel with a wire brush on one side and cleaned all of the old tarnish/residue off of it. I told the customer, maybe it will work until the new sensor comes in in a few days. What the heck, it was already out, right? Cleared the memory and sent him on his way. The bad temp sensor Check engine light never did come back on for him with the old sensor as long as I worked there. Who knows.

But the water temp sensor is fairly cheap so if you are going to go through the trouble of pulling it out, why bother.

And I always though most bad temp sensors that are consistently out of range, will trigger a CEL, no?

-Matt

[Richard]

I changed my temp sensor a couple months ago. It gave me problems for a while. Hard starting when the engine was hot, losing power on the freeway, etc. I had these symptoms for 2 - 3 months before it finally got bad enough and popped a CEL. I drove it for another 2 - 3 weeks after that, and I noticed something about the CEL. Sometimes the light would go off after a few seconds, sometimes it would stay on. Sometimes it went away after turning the car on and off, sometimes it didn't. Once I replaced the sensor, the car ran like a dream. In my opinion, even if there's no CEL present or in history, if you experience symptoms of a bad temp sensor, change it. It's cheap enough and pretty easy once you know where the sensor is (thank you Legacy Central).

[magicmike]

ok well I guess it wont hurt to pick one up this week.