Also, check your terminals to make sure they are tight and secure.
MPG Indicator Goes To Zero When Sitting
Thread Starter
Safety Car
Joined: Aug 1999
Posts: 3,750
Likes: 1
From: San Jose CA
MPG Indicator Goes To Zero When Sitting
I did a search and was surprised no one else has seen this, but then we all know the search engine is spotty at best.
This all started when I thought my gas mileage went into the crapper. I know how much gas it takes for my commute and I seemed to have used twice as much as I normally do. When I pulled into the garage yesterday I was just above 1/4 of a tank. I start it today and the Reserve warning light comes on, so I fill it, 15 gallons. The gauge shows full, but dang I didn't put that many miles on the last tank, something is not right.
I start monitoring the MPG indicator and it starts going up as I drive. I only go a short distance on the expressway to the store, and check it before I turn it off 17.5 MPG. Come out start the car and it is ZERO, WTF. Leave and it gets up 8.9 MPG, using a different route back to the house. Leave it in the driveway versus the garage, come back an hour later to move it into the garage and it is back to zero. The gauge still shows full.
Any clues?
FYI I reset the trip odo's to track the mileage on this tank.
Thanks
This all started when I thought my gas mileage went into the crapper. I know how much gas it takes for my commute and I seemed to have used twice as much as I normally do. When I pulled into the garage yesterday I was just above 1/4 of a tank. I start it today and the Reserve warning light comes on, so I fill it, 15 gallons. The gauge shows full, but dang I didn't put that many miles on the last tank, something is not right.
I start monitoring the MPG indicator and it starts going up as I drive. I only go a short distance on the expressway to the store, and check it before I turn it off 17.5 MPG. Come out start the car and it is ZERO, WTF. Leave and it gets up 8.9 MPG, using a different route back to the house. Leave it in the driveway versus the garage, come back an hour later to move it into the garage and it is back to zero. The gauge still shows full.
Any clues?
FYI I reset the trip odo's to track the mileage on this tank.
Thanks
Race Director
Joined: Jul 2007
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From: Reno is so close to Hell you can see Sparks , State Of Confusion
St. Jude Donor '12-'13-'14
Sounds like maybe you have a fuel sensor that is dirty, Do a search on it, Chevron Fuel has an aditive that helps, Techron or you can buy it at the auto parts store.
Bill
Bill
Tech Contributor
Joined: Dec 2003
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From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
The DIC mileage should be cumulative from when you hit reset. Normally it would start low and build up to a normal figure for round town driving. The readings you're getting seem like you'd expect for single journeys with a reset every time.
Seems like the system is not holding its memory rather than it being a gauging problem.
Are you showing any other indications of a bad battery? This type of thing can often occur when the battery starts to fail. Things like the HUD settings or memory settings can revert to default settings.
How old is the battery and could that be it?
Seems like the system is not holding its memory rather than it being a gauging problem.
Are you showing any other indications of a bad battery? This type of thing can often occur when the battery starts to fail. Things like the HUD settings or memory settings can revert to default settings.
How old is the battery and could that be it?
Last edited by DeeGee; Dec 28, 2008 at 04:04 AM.
Le Mans Master
Joined: Feb 2002
Posts: 6,937
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From: Waldorf MD
I'm betting on a bad battery. Does the DIC reset to odometer when you turn it off (if you had selected average MPG)?
When the cranking voltage falls below about 8.5 volts, the DIC looses it's temporary memory. This is due to a weak battery. Check the voltage, a 12-volt battery will measure at about 12.9 volts when it’s fully charged and about 11.4 volts when it is fully discharged. For final call, charge it fully and then do a load test (any store that sells batteries will normally do this for free). My C5 did this and my 800 CA battery tested at 250 CA.
When the cranking voltage falls below about 8.5 volts, the DIC looses it's temporary memory. This is due to a weak battery. Check the voltage, a 12-volt battery will measure at about 12.9 volts when it’s fully charged and about 11.4 volts when it is fully discharged. For final call, charge it fully and then do a load test (any store that sells batteries will normally do this for free). My C5 did this and my 800 CA battery tested at 250 CA.
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Perhaps a bad fuel sending unit - try some Techron and see if that help.
Instructor
Joined: Jan 2008
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From: SF Bay Area CA
Mine doesn't reset to zero, but it will usually lose 1 mpg from shut down to start up it if sits at least 8 hours. I have been watching mine as well since it seems my average has gone down 3-4 mpg.
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I'll jump on the bad battery/loose connection band wagon. If these cars get down in the 11.5vdc range, all kinds of electrical gremlins start showing up. A loose connection on the battery will do it too.
Your voltmeter may show that the battery is fine, but in reality it might not be holding the charge.
Your voltmeter may show that the battery is fine, but in reality it might not be holding the charge.
Race Director
Joined: Jul 2007
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From: Reno is so close to Hell you can see Sparks , State Of Confusion
St. Jude Donor '12-'13-'14
I'll jump on the bad battery/loose connection band wagon. If these cars get down in the 11.5vdc range, all kinds of electrical gremlins start showing up. A loose connection on the battery will do it too.
Your voltmeter may show that the battery is fine, but in reality it might not be holding the charge.
Your voltmeter may show that the battery is fine, but in reality it might not be holding the charge.
Burning Brakes
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From: H-Town Texas
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With all due respect Bill, the issue is that the average MPG is not retained when the engine is shut off. The alternator is nothing more than a DC Generator, that creates voltage when running, the battery is a storage device. If the storage device does not have ample charge in storage, then I still question either the connection to the storage device or the storage device's ability to store the charge created by the generator.
Race Director
Joined: Jul 2007
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From: Reno is so close to Hell you can see Sparks , State Of Confusion
St. Jude Donor '12-'13-'14
With all due respect Bill, the issue is that the average MPG is not retained when the engine is shut off. The alternator is nothing more than a DC Generator, that creates voltage when running, the battery is a storage device. If the storage device does not have ample charge in storage, then I still question either the connection to the storage device or the storage device's ability to store the charge created by the generator.
My bad.
Sorry.
I just re-read it, You are correct and I was wrong.
Bill
Thread Starter
Safety Car
Joined: Aug 1999
Posts: 3,750
Likes: 1
From: San Jose CA
Thanks everyone
I checked the battery connections and they are solid and pristine. Not a spot of corrosion to be seen. The battery is a 2 year old Interstate, while they can go bad, I have been using Interstate for pret' near twenty year now and never had one fail.
I will get a couple of bottles of Techron and see what happens. I suspect my gauge maybe flaky, because it was moving around on me, but I thought it was me, not paying attention. If it is the gauge/sensor it will be my second replacement. I had the dreaded gauge on empty about 7 years ago.
I checked the battery connections and they are solid and pristine. Not a spot of corrosion to be seen. The battery is a 2 year old Interstate, while they can go bad, I have been using Interstate for pret' near twenty year now and never had one fail.I will get a couple of bottles of Techron and see what happens. I suspect my gauge maybe flaky, because it was moving around on me, but I thought it was me, not paying attention. If it is the gauge/sensor it will be my second replacement. I had the dreaded gauge on empty about 7 years ago.
Tech Contributor
Joined: Dec 2003
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From: Horncastle Lincolnshire, England
2023 C5 of the Year Finalist - Unmodified
If the gauge is working normally and running down to zero I can't see that it can be the sending unit. If that was the problem the OP would be seeing the classic gauge issues rather than variations on the DIC.
Weird if the battery is good
Weird if the battery is good