Scanguage 2 issue? (MPG reading not matching reality on Jetta TDI)

[euromodder]

Looks like I've missed this one.

Originally Posted by SubSonic

I'm also having a little issue with a recently installed SGII into a Peugeot 206 1.6HDi. Currently moving towards my 3rd tank refill and calibrate, but the cars trip and odo reading are indicating a 80mpg reading while my SGII is reporting 59mpg. ( some hypermilling done to get 80mpg btw ).

What's your actual MPG when filling up ?

If you're actually getting 80mpg (which would be excellent !) it looks like you could use the 3/4 displacement rule

My gauge however does not show all of the sensors, with many blank. The one I'm am a liitle concerned about is the TPS ( blank ).

Diesels traditionally didn't have throttle
Though the recent ones with DPF etc. do have what is essentially a throttle valve.

Apparently, it's not reported on the HDi's in the way the SG expects a throttle.
TPS doesn't show on mine either.


I too have it set at 1.2L instead of 1.6L displacement.


PS :

If you have a DPF, it's possibly not reporting correctly during regenerations as the total fuel consumption apparently isn't reported in the signal on the OBD port where the SG expects the fuel use ...
On my car's OBC the fuel use goes up, instant and average, while on the SG it goes down during regeneration !

[UFO]

I am sure the reason why the SG does not report well on diesels is it uses similar algorithms that work well for gassers, that is fuel consumption based on air flow. That works reasonably well under load, where the computer will fuel up to the available air, but it falls apart at lighter loads and idle (coasting) because the computer will allow fuel ratios higher than even 20:1. So you calibrate the unit based on average fuel consumption, and you change your route or your driving style with a different mix of heavy and light loads, and your mileage calculations will be significantly off.

I calibrated my SG to my normal commute with the EGR disabled, and my driving technique is fairly consistent. Then I take a road trip. If it is along the front range, with few elevation changes and higher average speeds, my mileage will be slightly higher than SG calculations. If it is through the mountains, the SG calculations will far exceed the actual mileage.

My commuting mileage is about 45-46 mpg. A front range trip will get me about 40-42 mpg, and SG reports 39-41. A trip into the mountains will get me 50-53 mpg, but I've had the SG report upwards of 60 mpg.

[TEiN]

Originally Posted by UFO

I am sure the reason why the SG does not report well on diesels is . . .

I disagree with that.

I have a ScanGaugeII in my Ford F350 6.0 Diesel, and after adjusting the fillup % for the first few tanks, it was *dead-on-accurate*. Never more than 0.1 gallons difference between what the SC reported and what was actually pumped into the tank (on a tank that holds 38 gallons). I always filled at the same pump (except on long trips when that was impossible), and always filled it to the brim (until it wouldn't hold another drop without spilling over). It was accurate no matter if I was hypermiling it without any load, or towing a 10,000 lb trailer through the mountains going full throttle up all the hills.

For me, the ScanGauge works VERY well on diesels.

[UFO]

Originally Posted by TEiN

I disagree with that.

I have a ScanGaugeII in my Ford F350 6.0 Diesel, and after adjusting the fillup % for the first few tanks, it was *dead-on-accurate*. Never more than 0.1 gallons difference between what the SC reported and what was actually pumped into the tank (on a tank that holds 38 gallons). I always filled at the same pump (except on long trips when that was impossible), and always filled it to the brim (until it wouldn't hold another drop without spilling over). It was accurate no matter if I was hypermiling it without any load, or towing a 10,000 lb trailer through the mountains going full throttle up all the hills.

For me, the ScanGauge works VERY well on diesels.

Since I've only used it on a VW, let me be more specific.

The Scangauge does not report well on VW diesels. I think my data speaks for itself.

[NachtRitter]

Mine is definitely not *dead-on-accurate* on my VW TDI... but it is close enough that I can get an idea if I'm doing good on a tank or not. And that translates pretty well to daily, trip, and instant readings also. It doesn't really matter to me that I'm actually getting 45mpg when the SG says 41mpg... but it does matter to me that the SG says I'm getting 36mpg when I know I can do 41mpg on the same section of the road (over a single tank, I'm pretty good at reproducing trip FE numbers with the SG; across tanks its not too hard either). So even if the SG is off a little, it helps me improve my FE overall.

I do have a fairly consistent driving type... mostly freeway, very little city which probably helps.

[Josh8loop]

My SGII does pretty well once it's calibrated over a few tank fulls(850 plus miles) and driven under the same conditions every time. For instance, if my in town driving is calibrated correctly, then my Hwy reported MPG's are way off, and reported as frusteratingly low. I use mine for refference only, and rely on hand MPG calculation/ fully venting for accuracy.

[TEiN]

When you guys fill your diesels with fuel, are you always filling them to the very top, where you can see the fuel full to the end of the filler neck?

[NachtRitter]

I try as best as possible to fill consistently (always at the same station, same pump), but since diesel foams a bit it can be a pain... (fill til foam nearly overflows, then wait.... then fill til foam nearly overflows, then wait... and so on). So I'm probably not perfect every time.

[UFO]

The Scangauge resolution on fuel corrections is 0.1 gallon. As long as you fill the tank the same way each time, the minor variations will not matter.

[euromodder]

Originally Posted by TEiN

When you guys fill your diesels with fuel, are you always filling them to the very top, where you can see the fuel full to the end of the filler neck?

Until it shuts off automatically.
No topping off.

The little variations will even out with the next fill-up anyway.