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I don't understand this.

 
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  • 1 Post By LionPT
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Old 24 Dec 2019, 02:18 pm
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Default I don't understand this.

I haven't posted in quite some time and was pleasantly surprised and happy to see that the site is still alive and doing well.
Here's why I'm writing.
I recently bought another PT, a 2010, and decided to change the plugs since I didn't know what the condition of the plugs in it were. l disconnected the battery to clean the posts and to reset the computer so it will learn how I drive. So I get in the car today to run errands and notice the reading for gas mileage jumped from 20.5 to 24.5. I only started the car to make sure I didn't screw something up and the car didn't move. And while driving it today the mileage stayed in the same 24 mpg range. I always do the math for the actual mileage. What I don't understand is how would disconnecting the power change the gas mileage reading when the car didn't move?
Thanks for any ideas.
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Old 24 Dec 2019, 06:01 pm
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Default Re: I don't understand this.

It probably reset itself to 0, that's why the average changed. It will most likely change again once you start driving it more.
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Old 24 Dec 2019, 06:19 pm
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Default Re: I don't understand this.

Quote:
Originally Posted by LionPT View Post
It probably reset itself to 0, that's why the average changed. It will most likely change again once you start driving it more.
Exactly!
Disconnectig the battery resets everything that is not critical in the EVIC....like mileage.
So apparently, you have gotten 24 MPG in your first 10 miles!
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Old 24 Dec 2019, 07:50 pm
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Default Re: I don't understand this.

Quote:
Originally Posted by soonercruiser View Post
Exactly!
Disconnectig the battery resets everything that is not critical in the EVIC....like mileage.
So apparently, you have gotten 24 MPG in your first 10 miles!
I understand what you are saying but this number came up first thing after I changed the plugs and before I even drove the car after the plug change. Now if the mileage reading I had before I disconnected the battery, about 20.3, had shown up I could understand that, I'm curious how this number, 24, came up when the car hasn't been driven yet.
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Old 24 Dec 2019, 07:55 pm
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Default Re: I don't understand this.

Quote:
Originally Posted by Roadcuda View Post
I understand what you are saying but this number came up first thing after I changed the plugs and before I even drove the car after the plug change. Now if the mileage reading I had before I disconnected the battery, about 20.3, had shown up I could understand that, I'm curious how this number, 24, came up when the car hasn't been driven yet.
It's just an average, air/fuel mix, idle speed...you don't have to drive it for the sensors to read what's going on at that time. It could also be just some random number, you can always unhook the battery again & see what it says next. Don't worry about it, your just overthinking it...JMO
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Old 25 Dec 2019, 08:19 am
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Default Re: I don't understand this.

It's very possible that once the cache is cleared out, the number goes back to a factory default which may be 24 mpg. Since this number is accumulative over time, it makes sense to start at the "z-value" rather than at zero. A z-value is a target number for calibration that is close to the anticipated average. By starting here, the reading will reach the actual number faster than if it has to start at zero and then reach an average over time. Some analytical equipment works the same way. This shortens the cycle time until a statistically accurate number is reached.
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Old 28 Dec 2019, 12:41 pm
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Default Re: I don't understand this.

I love handy's explanation, very well thought out but for a PT PCM it really does not work that way. Also disconnecting the battery does not change any normal operating in the PCM like the widely thought re-learn that only some ECUs are able to do have not the PCM in a PT cruiser.
To reset the PCM you would actually need a DRBII or other diagnostic level equipment equal to its ability or to have a PCM flashed and or updated. Even re-setting the monitors will not change any operating programs in the PCM.

If anything I would say either recreate what you did and see if it does the same (which I sorta doubt it will.. sorta.... ) and chalk it up to an isolated anomaly. These PCMs (not ECU) do have and have been known over the years to some unexplained cliches that sometime will appear and then simply correct that were never really sorta out ... or explained.

I have run a PCM log recording around the town and light HWY use of my PT and then "tracking" (racing 1/4) and the PCM has no relearn or changes in the main cells like timing and fueling like many car with ECUs .
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