MPG

[Burner]

Can anyone explain how the "new" trucks attain their instant and AVG fuel economy data. Does it work off the TPS or a real regulator or meter of fuel in the system? I would like to know. If there iws a way I can find out, please let me know.


thanks, Burner

[Onebigcanuck]

I just got back from a 1200 mile trip with my 5th. I checked the mileage via the odometer and amount of gas to fill (top of the neck) tank.

I worked the mileage out and found it so close to what the computer said I quit checking it. I don't how it works but it seems to be fairly accurate.

[sdaver]

i would wonder how 305's would effect it........i dont think it would account for that...hey burner 205 345 3700 office......205 361 7721 cell......205 242 2202trk w/voice mail.....dave

[HDLD]

I don't know either but can also testify that it appears to be accurate. The "instant" economy setting is fairly quick to react. On a 55 mile trip this morning, starting out cold (32F outside temp.)it took a fair while (10 miles?) to come down to acceptable levels and in fact kept coming down right to the end. All hwy. miles at 1800-2000 rpm. At the end of the trip it was registering 20.6 mpg. I guess I need to commute further if I want better mileage. :eek:

I plan on using the spreadsheet that was made available here so will have some comparative numbers in a few weeks but as Onebigcanuck says, it seems fairly accurate.

[Burner]

I think that someone with oversize tires could give us an answer? If you had say... 285's we could deduce that the "speed-O" was off by 5%. We could check the AVG MPG on the computer, check the mileage and deduce what is happening. The mileage or MPG should be down by 5% to 7%. Five % for the rotation plus an extra 2% for the added drag/resistance. However, if the truck was calibrated for the tires...would the mileage still be off? That would tell us if the computer is in sync with the entire system, most likley running of a TPS, or an actual independant metering system. :confused: Any Idea's?

--> Burner

[TDIwyse]

HDLD

Have you looked at the instant mpg and how it varies with speed or rpm? I'm curious as to what happens to consumption figures over speed. For example, if you're cruising at 55 versus 60 or 65, what is the drop in instant mpg figures?

Also, what was your instant mpg when the truck was cold? You mentioned 20.6mpg after it was warmed up, but what was it when it was cold?

Any data would be appreciated.

[HDLD]

I'll have to observe it live this week to be accurate but if I recall, during the 1st mile it was quite high. I'm converting L/100km readings when I report since most here understand mpg. Seems to me the efficiency was cut in half or worse. I'll post on Tuesday or Wednesday night.

I'll be interested in the below freezing mileage later this year. This might help justify an Espar heating system purchase!

I also found that it goes up fairly quick when you stomp on it but I'm not sure how accurate it remains.

I think I was getting about 18.5 mpg at 75mph which isn't too bad but I'm trying to keep efficiency to a maximum.

It will also be interesting to note the effect on mpg when a mod is added, all else being equal.

[ 10-14-2002: Message edited by: HDLD ]</p>

[HDLD]

It's difficult to note changes in the instant mpg as you change speeds. This parameter is fairly sensitive. You would have to be on very level ground, perhaps using cruise. The slightest change in throttle/terrain will have an effect. Have to work on a more accurate test for 55 / 60 / 65 mph figures.

It was fairly cold this morning. Everything was coated with frost. I'd guess fuel efficiency was at least cut in half for the first mile. Didn't have the block heater plugged in. Stock unit. Started nicely and delivered heat fairly quickly after I got rolling. Idle time was only about 30 sec. Not sure how this compares to 1st mile in warm temps.

A better method might be to use one of the trip meters, reset it and drive off, noting the avg. mpg for 1 mile, reset, 2nd mile, reset, etc.

[TDIwyse]

HDLD

Thanks for your efforts. I'm probably one of the few concerned about fuel economy, but I got into diesel's with the VW's some time ago due to their economy.

Does anyone know of any aftermarket computer accessory that would enable a pre '03 to get the instant/average mpg info?

[HDLD]

I used to own a '98 Jetta TDI but found it to be too scary as a freeway commuter. I know they improved them a lot in '99+. Too bad VW won't bring their entire line of diesels to North America. A 6 cyl. Passat diesel station wagon might have kept me!

One area I go through daily requires a merge through FIVE lanes. Once in the Jetta, an accident occured there 4 cars in front of me and by the time I saw cars piling into one another, I couldn't stop faster than they were. Not a lot of damage but moved to a truck in 2000 and feel much more relaxed now when I commute. I feel I would have seen that coming in a higher vehicle. I can't count the number of times I've cruised to a stop in stop 'n go traffic and the guy in front has done a white knuckled panic stop.

It was a complete 180 as far as mpg are concerned but having had almost 3 yrs. to qualify my desire to continue driving a truck, I thought I'd fine tune the equation. Highest priority was fuel cost and longevity. CC for the kids was nice. Hopefully some day we'll have a 5er to keep it company. Looked at the Trailblazer but the lack of lateral support in the seats was incredible. Can't believe they did that! Also felt unstable going hard into corners.

So, with the Duramax, I'm hoping to save some substantial gas money. Of course I'll also have to tone down my driving but right now at just over 1/2 a tank, my average is 19.93 and towards the end of my commute this morning, I was doing 75mph for 10 mi. and this had no effect on my average. Didn't check "instant mpg" but if it was off significantly it would have eventually dragged the average down.

I'm beginning to wonder if the sweet spot isn't 2000 rpm instead of 1800 - at least when fully warmed up. This would be ideal for keeping up with the traffic. If I could get 20.5+mpg at 75mph, I'd be very happy.

To justify this purchase, I felt I had to see about a 5mpg increase. I used to average around 15.2 (admittedly could have been better with less aggression).

The mileage displays certainly help motivate! If it's reading 5 mpg, you might want to slow down. :eek:

The nice thing about trying to keep the truck in a mpg sweet spot is that the traffic won't intimidate you as much. I recall trying to do that when I had the TDI Jetta and gave up after a few weeks. People just try to force you along to their speed even though you're in the slow lane doing a few mph above the speed limit.

Obviously people aren't buying trucks for their fuel economy but it's interesting to learn what effect your driving patterns have on it.

*Update* On my last fill, the avg. economy registered the exact same as my calculation to 1 decimal point.

[ 10-24-2002: Message edited by: HDLD ]</p>