Trip computer MPG display
Thread Starter
Drifting
Joined: Oct 2012
Posts: 1,585
Likes: 28
From: Cedaredge Colorado
Trip computer MPG display
How accurate do you guys feel the reading displayed is during a trip. I just purchased a 99 FRC and went from San Diego to cedaredge CO and when I arrived home the avg?, what I'm thinking is displayed for the entire trip, displayed 31.7?????
Car has a few mods even and I'm fairly impressed if this is a accurate number
Car has a few mods even and I'm fairly impressed if this is a accurate number
Le Mans Master
Joined: Jun 2009
Posts: 6,528
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From: South Dakota
That is about what I get with my '99 FRC.
The avg. mpg readings on my FRC's DIC are pretty close, but slightly optimistic by about .2 or .3 mpg.
The avg. mpg readings on my '99 targa are optimistic by about 1.5 to 2 mpg. I have some mods and an HPtuners tune on it so that may have affected the readings although my actual mpg are better than the FRC.
I have seen a lot of comments on here about the DIC reading being off some.
These are amazing cars. Great performance and they are economy cars too.
The avg. mpg readings on my FRC's DIC are pretty close, but slightly optimistic by about .2 or .3 mpg.
The avg. mpg readings on my '99 targa are optimistic by about 1.5 to 2 mpg. I have some mods and an HPtuners tune on it so that may have affected the readings although my actual mpg are better than the FRC.
I have seen a lot of comments on here about the DIC reading being off some.
These are amazing cars. Great performance and they are economy cars too.
Last edited by QCVette; Apr 30, 2013 at 04:40 PM.
Melting Slicks
Joined: Aug 2003
Posts: 2,786
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From: Iowa
I think it would be great if Evil Twin would chime in on this because I've always wondered.
I imagine that the DIC computaton is likely based on actual distance travelled (which is accurate down to 1.3ft for what it sends to the speedometer, the PCM might be even more precise than that) and the known quantity of fuel injected based on the programed size of the fuel injectors, the number of injections which occur, and the pulse width of those injections.
basically...i don't see how anyone trying to verify the dic reading using the trip meter with 1 mile accuracy and the fuel pump reading (pretty acurate yes, but that reading is how much fuel you're putting in, which may only somewhat resemble how much fuel you burned) and think that the number on their calculator proves that the C5's trip comptuer must be inaccurate. given the likelihood of where those numbers come from, I'd say the DIC should be dead on and the trip meter/fuel pump or GPS "guestimate" would be the one that's a few off.
Of course it still seems odd that everyone who says they've checked always finds the DIC to be reading higher than whatever the other method is.
I imagine that the DIC computaton is likely based on actual distance travelled (which is accurate down to 1.3ft for what it sends to the speedometer, the PCM might be even more precise than that) and the known quantity of fuel injected based on the programed size of the fuel injectors, the number of injections which occur, and the pulse width of those injections.
basically...i don't see how anyone trying to verify the dic reading using the trip meter with 1 mile accuracy and the fuel pump reading (pretty acurate yes, but that reading is how much fuel you're putting in, which may only somewhat resemble how much fuel you burned) and think that the number on their calculator proves that the C5's trip comptuer must be inaccurate. given the likelihood of where those numbers come from, I'd say the DIC should be dead on and the trip meter/fuel pump or GPS "guestimate" would be the one that's a few off.
Of course it still seems odd that everyone who says they've checked always finds the DIC to be reading higher than whatever the other method is.
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I have found mine to be really accurate, within .3-.4 mpg. I can live with that.
Thread Starter
Drifting
Joined: Oct 2012
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From: Cedaredge Colorado
Thanks guys, my buddies are callin BS and saying no way a modded Vette gets anywhere near that.
Starting out was getting in the teens, by Barstow stop and go freeway action, some heavy foot action I was up to 26mpg, 85 mph AC to salida UT was up to 30, and by grand junction 31.7 mpg so pretty sure it's over the entire trip.
For how strong and hard this car pulls, 30+mpg is amazing, my Tacpma 6 cylinder only gets 25 in over drive with no wind, lol
And I'm really enjoying this car
Starting out was getting in the teens, by Barstow stop and go freeway action, some heavy foot action I was up to 26mpg, 85 mph AC to salida UT was up to 30, and by grand junction 31.7 mpg so pretty sure it's over the entire trip.
For how strong and hard this car pulls, 30+mpg is amazing, my Tacpma 6 cylinder only gets 25 in over drive with no wind, lol
And I'm really enjoying this car
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Only two tanks through my new baby but has been off about that much as well. I'm still loving it gets the best mileage in what's becoming our fleet!!
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Joined: Feb 2013
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From: South East TN
while on this subject, I was wondering if anyone else has this problem?
When I start my car the MPG display almost always resets to zero.
When I 1st turn the key to the on position the MPG display is whatever it was when I shut it down. As soon as I start it the display goes to the odometer, then when I set it to MPG display it's reading zero. Makes it about useless to use on any trips that require a stop and restart. Any Ideas?
Sorry about the highjack.
When I start my car the MPG display almost always resets to zero.
When I 1st turn the key to the on position the MPG display is whatever it was when I shut it down. As soon as I start it the display goes to the odometer, then when I set it to MPG display it's reading zero. Makes it about useless to use on any trips that require a stop and restart. Any Ideas?
Sorry about the highjack.
Advanced
Joined: Apr 2013
Posts: 62
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From: Fletcher North Carolina
while on this subject, I was wondering if anyone else has this problem?
When I start my car the MPG display almost always resets to zero.
When I 1st turn the key to the on position the MPG display is whatever it was when I shut it down. As soon as I start it the display goes to the odometer, then when I set it to MPG display it's reading zero. Makes it about useless to use on any trips that require a stop and restart. Any Ideas?
Sorry about the highjack.
When I start my car the MPG display almost always resets to zero.
When I 1st turn the key to the on position the MPG display is whatever it was when I shut it down. As soon as I start it the display goes to the odometer, then when I set it to MPG display it's reading zero. Makes it about useless to use on any trips that require a stop and restart. Any Ideas?
Sorry about the highjack.
Le Mans Master
Joined: Jun 2009
Posts: 6,528
Likes: 752
From: South Dakota
while on this subject, I was wondering if anyone else has this problem?
When I start my car the MPG display almost always resets to zero.
When I 1st turn the key to the on position the MPG display is whatever it was when I shut it down. As soon as I start it the display goes to the odometer, then when I set it to MPG display it's reading zero. Makes it about useless to use on any trips that require a stop and restart. Any Ideas?
Sorry about the highjack.
When I start my car the MPG display almost always resets to zero.
When I 1st turn the key to the on position the MPG display is whatever it was when I shut it down. As soon as I start it the display goes to the odometer, then when I set it to MPG display it's reading zero. Makes it about useless to use on any trips that require a stop and restart. Any Ideas?
Sorry about the highjack.
I had something similar where the avg mpg was resetting similar to what you describe almost daily. Mine was due to a low/bad battery. I started using a maintainer/charger and since then I have never had the problem again even after sitting for a couple of weeks to a month without the maintainer. My maintainer has a desulfation mode that can actually help restore a battery, and I suspect in my case it helped.
Like ploy22 said, you should have to hit the reset button to clear it back to 0.
Good luck.
Last edited by QCVette; May 1, 2013 at 06:19 PM. Reason: spelling
Race Director
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From: South East TN
Just to make sure, You do have it set to avg mpg not instant mpg. Instant will be zero when you are stopped at idle.
Le Mans Master
Joined: Jun 2009
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From: South Dakota
I went to some of the seminars at Funfest a couple years ago. One of them had to do with some common problems like the column lock and the battery draining when parked. The guy giving the instruction said to make sure that it has a 120 minute (or more) reserve capacity. He said that most of the problems are because people have the wrong batteries with less reserve capacity.
While I think his recommendation is good, my factory service manual for my '99 shows the battery specification to only be 90 minute reserve capacity.
When I looked for a battery I found that many batteries/stores do not even list reserve capacity. I did find ones with 120 or 90 that cost about the same, so I would go for a 120.
While I think his recommendation is good, my factory service manual for my '99 shows the battery specification to only be 90 minute reserve capacity.
When I looked for a battery I found that many batteries/stores do not even list reserve capacity. I did find ones with 120 or 90 that cost about the same, so I would go for a 120.
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Joined: Dec 2003
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From: Horncastle Lincolnshire, England
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I should start by saying that I pay £1.50 a litre for fuel so I pay loads of attention to gas mileage
In US speak that's over $9 a gallon depending on how you do the sums. I like to save my gas for when I can enjoy it and drive gently when I dont need to waste it.
You need to decide how you're going to use the 2 displays. Instantaneous is just that. It can be 3 mpg or 56 mpg depending on the throttle position.
Average mileage is the mileage over the period since you last hit reset. Try hitting reset quickly over about 10 minutes when you're driving and you can get big differences depending on whether you are driving gently at 50, gently at 80 or hitting the throttle. Leave it for a full trip cycle and you'll get somewhere between 18 and 25 depending on how sensible you are
The point I'm making is when do you hit reset? If its over a single tank of gas and you check how much you put in and do a manual calculation you'll get a decent average. If you hit the highway and play gentle with the throttle you may get 30+. You can do way better if you try.
Decide what you want to measure and use the system properly. It'll give good readings.
In US speak that's over $9 a gallon depending on how you do the sums. I like to save my gas for when I can enjoy it and drive gently when I dont need to waste it.You need to decide how you're going to use the 2 displays. Instantaneous is just that. It can be 3 mpg or 56 mpg depending on the throttle position.
Average mileage is the mileage over the period since you last hit reset. Try hitting reset quickly over about 10 minutes when you're driving and you can get big differences depending on whether you are driving gently at 50, gently at 80 or hitting the throttle. Leave it for a full trip cycle and you'll get somewhere between 18 and 25 depending on how sensible you are
The point I'm making is when do you hit reset? If its over a single tank of gas and you check how much you put in and do a manual calculation you'll get a decent average. If you hit the highway and play gentle with the throttle you may get 30+. You can do way better if you try.
Decide what you want to measure and use the system properly. It'll give good readings.
Last edited by DeeGee; May 3, 2013 at 03:00 PM.
Melting Slicks
Joined: Aug 2003
Posts: 2,786
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From: Iowa
my best ever was on a 5 hour trip across the state. state highways, 60mph limits for the most part but also runs through towns with stop lights. I reset the reading when I started off, and took a picture when I stopped in my driveway...reading 35.7.
Approximately 5 hours driving on that calculation.
I have never seen it that high before or since, but 33 frequently, 34's a few times (2+ hour drives)
Approximately 5 hours driving on that calculation.
I have never seen it that high before or since, but 33 frequently, 34's a few times (2+ hour drives)
Le Mans Master
Joined: Nov 2006
Posts: 7,215
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From: Orlando FL
Tell your Buddies they need to buy a Vette
Thanks guys, my buddies are callin BS and saying no way a modded Vette gets anywhere near that.
Starting out was getting in the teens, by Barstow stop and go freeway action, some heavy foot action I was up to 26mpg, 85 mph AC to salida UT was up to 30, and by grand junction 31.7 mpg so pretty sure it's over the entire trip.
For how strong and hard this car pulls, 30+mpg is amazing, my Tacpma 6 cylinder only gets 25 in over drive with no wind, lol
And I'm really enjoying this car
Starting out was getting in the teens, by Barstow stop and go freeway action, some heavy foot action I was up to 26mpg, 85 mph AC to salida UT was up to 30, and by grand junction 31.7 mpg so pretty sure it's over the entire trip.
For how strong and hard this car pulls, 30+mpg is amazing, my Tacpma 6 cylinder only gets 25 in over drive with no wind, lol
And I'm really enjoying this car
I had a heavily modded 98 that got about 30-31 cruising. My supercharged 03 vert got 28.x on a 7 hr road trip. It makes over 450 RWHP and still gets 28 mpg (when you are easy on gas) 
as for accuracy I would think based on how often you reset it and where you are driving it should be fairly accurate.
I know based on refueling the car on trips the highway accuracy has to be pretty close.
