car runs funny when cold

[tsieagletalon]

my car wont run well and it gets shitty gas milage untill its nice and warmed up what the problem with it

 

[delta448]

From my experience that's pretty normal. I think it's because the O2 sensor has to heat up to read accurately. Just take an extra couple of minutes and let it warm up. If it's taking a really long time to get warm or if you still get bad mileage after it's warm I'd be more worried.

 

[Gst18]

Usually if its really cold weather and you first start your engine it will run really crappy because it will run off of the engine coolant temp. sensor. The engine coolant temp. tells the computer how much fuel to give the engine until the O2 sensor goes into closed loop. The O2 sensor will be in Open Loop until the tempeture reaches up to 600 degrees F.

Hope this helps explain why it gets crappy gas milage until its warmed up.

 

[oldman]

Usually if its really cold weather and you first start your engine it will run really crappy because it will run off of the engine coolant temp. sensor. The engine coolant temp. tells the computer how much fuel to give the engine until the O2 sensor goes into closed loop. The O2 sensor will be in Open Loop until the tempeture reaches up to 600 degrees F.

Are you sure about that?

OP,

1. Are you trying to boost before the car warms up?

2. Car should run rich until it goes into close loop, it shouldn't run shitty unless there is a problem, coolant temperature seonsor included.

3. How do you know what the gas miliage is before the car warms up? How are you measuring this since it only take 5 mins to reach operating temperature?

 

[Defiant]

If you're noticing how long it takes to warm up, you probably have a failing thermostat. DSMs are almost fully up to temperature within about five minutes.

 

[redeclipse7782]

If you let your car sit overnight in the cold then you wake up turn on the car and immediately start beating on it of course it is going to run like shit. Its true the car does operate in open loop (rich) until a certain temperature. I thought it was when the thermostat opened, but I could be wrong. I let my car idle for atleast 5 minutes before I drive it no matter what season it is, gets everything warmed up and well lubricated. If you treat your car well it will treat you well.

 

[steve]

Usually if its really cold weather and you first start your engine it will run really crappy because it will run off of the engine coolant temp sensor.

The engine coolant temp tells the computer how much fuel to give the engine until the O2 sensor goes into closed loop.

The O2 sensor will be in Open Loop until the tempeture reaches up to 600 degrees F.

That's an interesting way to look at it?

The ECT is one of the sensors the ECU uses for enrichment during warm up but if everything else is working correctly the engine doesn't run crappy, just a littler richer than when it is warmed up.

The O2 sensor doesn't go open or closed loop the ECU does. The O2 sensor is always active. The sensor does not begin to generate it's full output until it reaches about 600 degrees F but it does start producing a voltage pretty quickly. That's one reason why we use sensors with a built in heater to shorten the time it takes to reach it's operating temp and to stabilize the temp in various low speed cases.
A broken or burned out O2 heater can cause the type of problem the OP is having. It sometimes shows up as a sensor with erratic or no output at idle and part throttle.

The ECU doesn't have any direct feedback of the sensors temp so it doesn't factor into open/closed loop decisions like things the ECU can measure do.

There is a timer thats starts when you start the engine and ECT checks before the ECU will start dithering the idle mixture. One change made between 90 and later cars is that temp check with 90 cars waiting until about 106F and the later cars starting at 86F before trying to enter closed loop operation. The ECU doesn't start updating the fuel trims until the car as fully warmed up and the ECT is >= 186F.

Logging a normal car will show the O2 sensor output starting out around 0v when you start the car and quickly rising to the rich side of stoichiometric as it heats up. Once the timout expires and the ECT is greater than the threshold above the ECU will attempt to lean the mixture and watch for the sensor voltage to drop below the stoichiometric switching point. If it does the ECU will enter closed loop and switch back and forth between raising the AF and lowering it based on the switching of the sensor around stoichiometric. This causes the average AFR to be 14.7:1. The ECU is always calculating a 14.7:1 AFR based on the air mass per rev. The difference between it's calculations and the O2 sensor feedback is a error value that will be averaged into the closed fuel trims once the engine reaches operating temp and you will see this when logging.

Steve