Chevy Truck, Confirm/Dispel my "finding"

How fast are you driving to get 16mpg? If you're driving 80mph that would explain it. Normally you would have a check engine light if you had a mechanical problem causing you to get such poor mileage.

I have a 5.7l 94' 2500 suburban that weighs a ton (well, 3.5 tons) and I get close to 16mpg highway. When I bought it, it got 12. Just needed some tune up stuff.
 
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Tom-D said:
and pull like hell. :)
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Reaffirming my point you need them for pulling full time and that's it.

I see more diesel's hitched to nothing than otherwise.

Meanwhile, the torque/payload figures on the gas trucks have gone up. :yesnod:
 
ron22 said:
Real bad and answer to you original question.
They take gas burned divided by MPH.
Since MPH = 0 they get a division by Zero error.
So easy fix is
If MPH != 0 then gas burned divided by MPH
So we just ignore when MPH = 0 so the reading is off.

Now this thread can go off track and talk about how to programmer are not that dumb. :D
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Yeah I thought that was obvious too. And continued in my response to say that the computers on board are not calibrated in any meaningful way. The details of that are...

They make assumptions about the size of the tank by not including how much more fuel goes in after the sensor reads "full" (you can fill the filler pipe you know -- any change in the gas gauge? Nope.), and assumptions about where "empty" is (there's a reserve) and generally the manufacturers use the numbers that'll make them look the best.

As far as the EPA testing, if they started testing light trucks it's news to me. They didn't used to. Good for them. Think of the children. :)

Not sure what the OP wants, other than a meeting with one of the engineers. Maybe one will show up on a free *aviation* forum. LOL. :rollseyes:
 
ron22 said:
Real bad and answer to you original question.
They take gas burned divided by MPH.
Since MPH = 0 they get a division by Zero error.
So easy fix is
If MPH != 0 then gas burned divided by MPH
So we just ignore when MPH = 0 so the reading is off.

Now this thread can go off track and talk about how to programmer are not that dumb. :D
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That would make sense though because adding the time sitting at stoplights and stop signs together with the amount of time I let the truck idle when I quickly grab something would come a lot closer to the 0.5 gallons that it's typically off.
 
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denverpilot said:
Just don't be this dumb... He broke the truck and himself.

http://youtu.be/JKQdlXvbWSU
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:eek::lol:

I don't do dumb redneck stuff like that...

...I do other dumb redneck stuff :D

OP I am truly sorry for the participating in one of the thread detours. It's just that the original question you posed is not very interesting to me but I found some of the tangents to be so. Again, my apologies. ;)
 
Tom-D said:
and pull like hell. :)
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Too bad the dodge transmissions don't!

I had an 08 Dodge 3/4 ton cummins that I bought new and traded for my 11 Chevy.

Worst truck I've ever owned. Very uncomfortable, back to the shop for countless recalls, front hubs went out at 60k miles because they weren't heavy enough to carry the cummins, and it loved to eat turbos. Ate three of them. The last time it took out all the sensors both incoming and outgoing along with the particulate filter. IIRC they said the bill for that one would' ex been about $6k had it not been under warranty but thankfully, it was all covered under warranty so the only headache was how often it was in the shop...which was often...but there was no way I was going to own that truck once the warranty expired. No effin' way.
 
timwinters said:
Too bad the dodge transmissions don't!

I had an 08 Dodge 3/4 ton cummins that I bought new and traded for my 11 Chevy.

Worst truck I've ever owned. Very uncomfortable, back to the shop for countless recalls, front hubs went out at 60k miles because they weren't heavy enough to carry the cummins, and it loved to eat turbos. Ate three of them. The last time it took out all the sensors both incoming and outgoing along with the particulate filter. IIRC they said the bill for that one would' ex been about $6k had it not been under warranty but thankfully, it was all covered under warranty so the only headache was how often it was in the shop...which was often...but there was no way I was going to own that truck once the warranty expired. No effin' way.
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FYI:

A fleet mechanic told me unlike a gas car, NEVER back up and then put it in drive without coming to a complete stop first. This will blow your tranny every time on a diesel. :mad2:
 
timwinters said:
Actually, Nate, it was a really simple question.







Reading is fundamental.
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And the answer is: Doesn't matter. 0 MPG is 0 MPG and if the stupid thing doesn't read that the fuel level is going down while in park, it should still "catch up" when taken OUT of park if it's measuring mileage divided by fuel used.

The error is not caused by "turning off the computer" unless the computer programmer isn't doing the above math. Simple division fixes it in one CPU clock cycle as soon as you take it out of park if they really did shut down the calculations.

The question, as posed, isn't a feasible reason for the error in the first place.
 
narchee said:
OP I am truly sorry for the participating in one of the thread detours. It's just that the original question you posed is not very interesting to me but I found some of the tangents to be so. Again, my apologies. ;)
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No worries, we're good. And I'm certainly not mad about anything, I think it's funny more than anything because it is so representative of how the majority of the threads here go.

FWIW...my original "diatribe" (as R&W called it) was meant to be more of a George Carlin skit than a Bill O'Reilly smack-down.
 
dell30rb said:
How fast are you driving to get 16mpg? If you're driving 80mph that would explain it.
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I drive about 5 over everywhere I go so, yeah, that might affect the highway mileage but not the city.

In fact, most of my driving is "combo" because I live 10 miles out of the small town near me and 30 miles from the larger one with more options for shopping/eating. I get to both of those towns on 55 mph roads. I average about 14 to 15 doing this typical "combo" driving. On average the truck gets about 2/3 the gas mileage advertised (based on manual calculations...not the computer).

Then, on top of that, the gas mileage increased by about 5% when I put a camper shell on it. It used to be a bit worse even.

It's been back in the shop a few times to be checked out..."nothing's wrong" (note the quotation marks).
 
Don't know if I can help much because I too have no definitive answer. Here's my experience; 09 Saturn Vue(GM) with hybrid. When the engine is on, and the car is stopped the MPG display shows "--", two dashes. When I put it in N and let it coast, it goes to "99" indicating the highest it will read. So, the MPG indicator knows when the car is in motion and when it isn't.

Like others have noticed, the MPG indicator isn't very reliable. I tested with the fuel used over odometer tracking and the onboard MPG indicator was always 1-3MPG higher than actual. In my case, I don't thing it has anything to do with the MPG counter running when the car is idling. I tested it during a full tank run on the freeway without any idling and it was still in error by ~2MPG. It read 31.7 and my actual consumption was very close to 30MPG. I checked my odometer against the highway mileage signs and the error was very small over 10 miles, so that didn't account for it either. I think that the algorithm used for averaging MPG on cars is very generous, and certainly not a fuel totalizer. Which makes sense because to use a fuel totalizer they would need both a consumption metering servo, and a return metering servo for the fuel returned to the tank, as almost all modern FI systems are continuous flow, fixed pressure(the 1999-2007 Ford small 4cyl engine is an exception).

So, in summary, although my MPG meter reads out in tenths of a significant digit; "NN.N", the accuracy is plus or minus 2MPG, so the last digit is worthless and the accuracy can't be trusted much.
 
Check the mileage on your computer versus that shown on the odometer. Mine are different. Mileage usually calculates out less than 1mpg different. But then again, she's old enough to have a mechanical odometer, and a voracious thirst for all fluids except water.
 
I love that pilots are discussing the accuracy of fuel gauges and totalizers in trucks, when no one here would ever trust the fuel gauge is a 172! :D
 
N747JB said:
I love that pilots are discussing the accuracy of fuel gauges and totalizers in trucks, when no one here would ever trust the fuel gauge is a 172! :D
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I think you missed that most of us don't trust the fuel gauges in our trucks either. ;)

We have one vehicle out of all of them here at home, that the fuel gauge reads anywhere near accurately.

I reset the trip odometers at every fill up. Habit. A hint when you hit X miles that it's time to fuel up. Plus it allows for that whole manual mileage calculation thing. :)

Right now the entire instrument cluster in the Yukon is dead again. No speedo, no fuel gauge, no nothin. Heh. You'd better know how many miles you drove...
 
denverpilot said:
Right now the entire instrument cluster in the Yukon is dead again. No speedo, no fuel gauge, no nothin. Heh. You'd better know how many miles you drove...
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there's a guy in our area that fixes those for $100 and guarantees his work for as long as you own the vehicle...far better than the $500 or $750 (or whatever it is) that the local chevy dealer wanted. The cluster in my 02 truck wagged out about a year ago and he fixed it. No more problems thus far.

He also installed a new multi-function switch for me since some of the features on mine weren't working. You know the switch...the blinker, cruise, windshield washers & wipers, brights and whatever else that thing controls....I think it even flushes the toilet at the local convenience store.

I had to turn on my left blinker to get the windshield washer to work...no joke...felt like Jed Clampett! Chevy wanted almost $500 just for the switch and I forget how much to put it in. This guy directed me to an online seller that was less than $100 and he installed it for $90.

Sometimes, these small town honyocks know their sh*t. This one certainly does when it comes to chevys
 
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timwinters said:
there's a guy in our area that fixes those for $100 and guarantees his work for as long as you own the vehicle...far better than the $500 or $750 (or whatever it is) that the local chevy dealer wanted. The cluster in my 02 truck wagged out about a year ago and he fixed it. No more problems thus far.



He also installed a new multi-function switch for me since some of the features on mine weren't working. You know the switch...the blinker, cruise, windshield washers & wipers, brights and whatever else that thing controls....I think it even flushes the toilet at the local convenience store.



I had to turn on my left blinker to get the windshield washer to work...no joke...felt like Jed Clampett! Chevy wanted almost $500 just for the switch and I forget how much to put it in. This guy directed me to an online seller that was less than $100 and he installed it for $90.



Sometimes, these small town honyocks know their sh*t. This one certainly does when it comes to chevys
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They're all over the Internet. Fixing broken GM clusters is big business.

I did the servo replacement on mine myself with $20 in parts from China and a de-soldering workstation and iron.

The power supply and VFD problems are less documented and harder to find parts for, or I'd finish the rebuild. And there's a pretty good chance I've got one of the badly soldered diodes somewhere on the board in the power supply section, the way it's acting. That or the lovely round-pin-in-square-holes moronic connector on the back isn't working well, but I've already disassembled that thing and re-crimped all the power connections.

And then there's the possibility of bad capacitors...

I'll be pulling it and sending it to one of the rebuild guys. They apparently have time for this BS.

Just haven't cared enough to take it out and box it up yet. I just use the iPhone in a RAM mount for a speedo and drive it.

They'll also replace all the grain of wheat light bulbs with LEDs that'll outlast the truck if ya like. Kinda looks neat. I can't decide on white, red, green, or blue. ;) Green probably matches the other VFD on the stereo and the other lights in the cabin that won't get LED replacements. Or white. Red looks kinda nifty though. Blue looks a little too "rice rocket mod kid style". :)
 
If I ever get pulled over for speeding I have this for the judge.

The speedo was like this for a few weeks then went back to working normally one day.

 
So, I've done some follow up tracking and documentation since making my original post a few weeks ago and have come to the conclusion that the computer does not count any gas used while the vehicle is sitting still. The vehicle doesn't have to be in park, just sitting still.

I took a trip to KC last weekend the computer matched exactly how many gallons I actually burned...checked it both directions. Around town, I always pump 1/4 to 1/2 gallon more than the computer says was used. I've not let the truck idle in park at any time during this follow-up testing.
 
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timwinters said:
So, I have a 2011 Chevy 1500 Silverado with a 5.3L engine. Hate it. It's not 1/2 the truck my 2002 Chevy is. One major issue is that the mileage was supposed to be in the 21/17 range and I'm lucky to get 16/13.
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Driving style, letting it idle, weather, can make more than this much difference.

Then when I fill it up, I'll always put 1/4 to 1/2 gallon more in it than the computer says I used. So the mileage is worse yet...double whammy.
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1/2 gallon out of 20 is 2.5%. Not much difference.

I filled up yesterday and put over 2 gallons more in it than the computer indicated had been burned. What changed last week is that I "warmed it up" at length almost every day because we have a foot of snow on the ground and had two mornings with lows around -15dF.
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Say goodby to your fuel economy...

So, my theory is that the "computer" only counts gas burned when the truck is in gear...it doesn't count gas burned in park. That would also explain why it's typically off by a fraction of a gallon because I tend to leave it running when I run into the post office or convenience store (small town bad habit).

Does anyone know if the computer shuts off in park?
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I seriously doubt it. If it did, then it wouldn't be able to give you a running total of the fuel used. I realize that the engineers over at Chevy are not as smart as the ones at Ford, but I doubt that they are this dumb.

Now, at idle the fuel pulsewidths are very low - and by far, this is the least accurate operating region as far as the actual fuel delivered vs. fuel mapped. So, more idling could result in more overall discrepancy.

Of course, more idling results in more wasted fuel and lower fuel economy. Stop doing that if you care about the numbers. Also, stop driving over 75. 65 is even better. Minimize the use of brakes - let your foot off the gas and coast instead of driving up to something and using the brakes. With a little effort (and warmer weather) you can beat the sticker numbers.
 
My land lady will leave her van sit there and idle with the A/C running sometimes for hours, then she complains about the mileage.:mad2::mad2::mad2::rofl:
 
dell30rb said:
If I ever get pulled over for speeding I have this for the judge.

The speedo was like this for a few weeks then went back to working normally one day.

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Good luck, I have a feeling they'd just hit you with a faulty equipment ticket on top of the speeding ticket or something.
 
I have 70K on my Toyota Tundra Double Cab. I have never one time checked the mileage, I do know it's not all that great. I didn't buy it for mileage, I bought it to tow my boat, my hot rod and anything eles that I need to. I haul stuff in the bed, this is why I bought a truck, mileage does not bother me as long as the truck works for the job I bought it for.
 
2007 F350/6.2Powerstroke/Crew/SRW/longbed
22' TopHat flatbed gooseneck
20' Hanover gooseneck cattle trailer
1964 Cessna 180

It's one heck of a long truck/rig but it rides like a dream. Not having duals and I think the camper suspension package with bigger sway bars makes a big difference. It takes corners like it's glued down. The integrated adjustable trailer brakes are great.

It's no 20m.p.g. mall crawling vehicle, but it sure can haul smoothly and with authority. :)
 
Okay, in the interest of science, I did one more test. I started the truck tonight and let it run in the driveway for an hour. When I first started it, the computer was showing 17.6 gallons used since last being reset. After an hour it showed 18.2 gallons.

Thus it doesn't discount fuel used when sitting still so I really don't know WTF is going on.

All I know is that it accurately tracks the fuel burned when driving on the highway but doesn't when driving stop-n-go in the city. The MPG calculator matches the tripometer/recordedfuel burn...not actual fuel burn.
 
timwinters said:
Okay, in the interest of science, I did one more test. I started the truck tonight and let it run in the driveway for an hour. When I first started it, the computer was showing 17.6 gallons used since last being reset. After an hour it showed 18.2 gallons.

Thus it doesn't discount fuel used when sitting still so I really don't know WTF is going on.

All I know is that it accurately tracks the fuel burned when driving on the highway but doesn't when driving stop-n-go in the city. The MPG calculator matches the tripometer/recordedfuel burn...not actual fuel burn.
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See post 61. Accuracy of fuel consumption measurement is decreased while idling.
 
jesse said:
See post 61. Accuracy of fuel consumption measurement is decreased while idling.
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Well, except that 0.6 gallons for an hour of idling is pretty accurate. And I don't idle nearly that much during one tank of routine driving so that wouldn't seem to explain an error of nearly a 1/2 gallon at a 20 gallon fill-up.

Unless I'm missing something...which is always quite possible with me! :goofy:
 
timwinters said:
Well, except that 0.6 gallons for an hour of idling is pretty accurate. And I don't idle nearly that much during one tank of routine driving so that wouldn't seem to explain an error of nearly a 1/2 gallon at a 20 gallon fill-up.

Unless I'm missing something...which is always quite possible with me! :goofy:
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2.5% isn't much of an error.
 
Same gas station? Same pump? Stop when the nozzle clicks off? Many variables in filling up.
 
txflyer said:
FYI:

A fleet mechanic told me unlike a gas car, NEVER back up and then put it in drive without coming to a complete stop first. This will blow your tranny every time on a diesel. :mad2:
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I was taught to come to a complete stop regardless of the powerplant. It's not good on any transmission to torque it in the opposite direction. The diesels generally just have the torque to cause damage quicker.
 
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