Best live fuel mileage estimator for our vehicles

[thechoochlyman]

I have an Ultragauge, but it doesn't work right. Is there anything out there that doesn't need calibration?

 

[Tdijarhead]

pen & paper

 

[thechoochlyman]

Ha, yeah. I've been keeping track of MPG ever since I bought the car. It would be nice to have a live readout though in order to see at what speed I have the best MPG.

 

[john.jackson9213]

I had my MFA trip economy very close to accurate and repeatable. But since the new turbo and Race 520 nozzles, it is way, way off. Everyone I have spoken to about the issue tells me there is no good solution because we are not measuring actual fuel flow into the engine. Only guestimating based on IQ. Now my 11mm pump flows more fuel and R520 nozzles flow more fuel, so IQ is cut way back. That throws off the Gustimated fuel economy calculated by the MFA.
Now, I also have a ScanGaugeII and it does have some adjustments. Over the next few months, I will be playing with those adjustments to see what I get compared to pen and paper.
One more thing. Because diesel is such a foamy fuel, it is difficult to refill the fuel tank to exactly the same level every time, even with a vented tank. BUT, I am/will be using Propel HPR fuel, which does not foam near as much as D2, so that will help me when I am in San Diego.

 

[FordGuy100]

A long time ago, I looked into fuel flow gauges. Essentially you spec them out for the appropriate fuel line size (lets say ID 1/4"), and the gauge will tell you the exact fuel flow rate. Problem is, with a diesel, we have return lines that push a lot of fuel back into the tank. Thus we would need two of them, then subtract the difference.

Now I'm thinking we can find some sort of electric fuel flow "sender" of sorts, and then use some sort of DIY programing on something like a arduino. Something like this? http://myemail.constantcontact.com/...ation.html?soid=1102692382577&aid=p1Ia81lroa4

http://forum.arduino.cc/index.php?topic=124115.0

 

[annieneff]

Scangauge II is pretty customizable if you play to its strengths.

1. Don't fill your tank up all the way. You'll never get an accurate measurement that way. Just put in 10 gallons (or however much you want, as long as you can put exactly that much in again next time) over a series of predetermined trip odometer resets, and do the pen and paper method.

2. Once you're sure of your mileage, calibrate said Scangauge. You calibrate it by changing the gas tank size, and the liter engine size. I haven't messed with diesel a, and diesel b, but you might monkey with those too. Between the first two presets though, I've been able to dial my scangauge in pretty well.

For instance: on my old b4v I set my fuel tank size at 27 gallons, and had the engine size at 2.0 liters (it was tuned/injectors/etc). This got me to within 5 miles over a 10 gallon tank. Not too shabby.
My new b4v is set at 25 gallons for the tank and the 1.9 liters, and so far it pencils out to within 10 miles per 10 gallons. Again, pretty good.

Anyway. Hope that helps. I haven't owned anything else, so maybe there is something better, but the scangauge seems pretty darn good to me.

Andrew

 

[turbodieseldyke]

If you go the DIY Arduino route, build a MPGuino. Feed it the VSS signal, and the Fuel Consumption signal from the ECU, and (if you never change the IQ) you only need to calibrate it once. It will give you instant readings, averages, more than you want. The code is opensource, so you can custom program it, if you're so inclined.

The signals are easy to get on the Passat. The Jetta is worse, because you need to add the Fuel Cons wire to the wiring harness, and run it from the ECU to your gauge.

 

[thechoochlyman]

Figured I'd update this - I got my Ultragauge working properly yesterday. The screen on it was messing up, and turns out the ribbon cable has a short. I have it going for now.

The odometer reading was pretty close, I have it multiplied to 1.038 in the gauge settings. The fuel was way off though, I have it around .307 for now and still need to fine-tune it. I suppose I'm telling all this to confirm that the gauge does work with our cars.

 

[Lug_Nut]

Closed 'throttle' when coasting in gear shows what instantaneous MPG?

 

[thechoochlyman]

About 60~ish, IIRC. Coasting downhill in neutral is like 150, though.

 

[john.jackson9213]

Glad to see this thread updated and the Ultragauge working properly.

As a note for future readers with a 1996 Passat. The OP has a 1997 Passat and is OBD2 complaint, so the Ultragauge and Scangauge work to show information from the car's ecu. The 1996 Passat is not just plug and play OBD2 compliant. The original black plastic BK type ecu is only OBD1 compliant. That means it does not work well with the Ultragauge/Scangauge. The 1996 Passat needs to have the late 96 aluminum case GQ ecu to work properly with the Ultragauge/Scangauge.

 

[turbodieseldyke]

About 60~ish, IIRC. Coasting downhill in neutral is like 150, though.

That's weird. Coasting in gear should be 999 or 999,999 or infinity, since zero fuel is being consumed. Maybe the Ultragauge reads things differently.

 

[Lug_Nut]

Closed 'throttle' when coasting in gear shows what instantaneous MPG?

About 60~ish, IIRC. Coasting downhill in neutral is like 150, though.

Glad to see this thread updated and the Ultragauge working properly.

I suspected not, and that's why I asked.
Now I have no doubt that it's not working correctly.

The Ultragauge is using the MAF and air flow to guestimate the fuel use. Perfect for a throttle plate equipped engine and a regulated air and fuel ratio, but useless in a diesel with unregulated air flow.
You won't get accurate fuel use when measuring unrelated air use.

 

[john.jackson9213]

I suspected not, and that's why I asked.
Now I have no doubt that it's not working correctly.

The Ultragauge is using the MAF and air flow to guestimate the fuel use. Perfect for a throttle plate equipped engine and a regulated air and fuel ratio, but useless in a diesel with unregulated air flow.
You won't get accurate fuel use when measuring unrelated air use.

Lug_Nut:

Does the Scangauge also use the MAF and air flow to guestimate fuel use? Or does it use the Injection Quantity to guestimate fuel consumption?

 

[thechoochlyman]

So our fuel pump cuts fuel completely upon deceleration?

 

[Lug_Nut]

Does the Scangauge also use the MAF and air flow to guestimate fuel use? Or does it use the Injection Quantity to guestimate fuel consumption?

From what I have read and seen the Scanguage is alone in correctly interpreting fuel use by measuring fuel use. All the other plug-in monitors I have investigated use air flow.

So our fuel pump cuts fuel completely upon deceleration?

Ummm, yes and no. There is still fuel being moved to and from the tank and recirculated within the pump, but none is injected for combustion. As RPM drops closer to idle the injection quantity gradually increases, starting at about 1100 and under full ECU control by the 900 rpm idle.
The fuel injection quantity INCREASES even further as rpm drops below the idle rpm in attempts to prevent the engine from stalling.

 

[turbodieseldyke]

I know the Torque OBD2 app for Androids reads MPG differently for gas and diesels. The Free version of the app won't do diesel at all; you have to get the paid version for $5 or so.

Further note to the Coasting MPG question - Coasting downhill in neutral should be alot higher than 150, so that's wrong too. It should be 300-600, depending on your speed (roughly 10x your MPH).

 

[thechoochlyman]

...but none is injected for combustion.

That's what I needed to know.

Ok, all this makes sense. I'm not sure if there's any way to make the Ultragauge recognize fuel injection quantity, but it may be something to investigate.

Even still, measuring air intake instead of IQ, would this not still be a good meter to find best MPG at specific RPMs, even though the value itself may be incorrect?

 

[Ol'Rattler]

One more thing. Because diesel is such a foamy fuel, it is difficult to refill the fuel tank to exactly the same level every time, even with a vented tank.

What you do is set the nozzle on low and after it shuts off, you slowly keep adding fuel. It will foam some so what you do is let the bubbles dissipate and slowly fuel some more.

After a few times of doing this, you will end up with clear fuel just shy of spilling over the filler neck. Extremely accurate, and only takes a couple of more minutes to do.

Pen and paper calculations are the only accurate way to calibrate what ScanGage is telling you.

I think the method for calculating MPG described in post #6 would be accurate, as well, but still pen and paper.

 

[Lug_Nut]

Even still, measuring air intake instead of IQ, would this not still be a good meter to find best MPG at specific RPMs...

The air flow is somewhat independent of the fuel use. The engine load / power production is not related to the air flow.
At 2000 rpm coasting in gear down a hill the air flow through the MAF sensor is some number.
At 2000 rpm on a flat and level road there is almost exactly the same air flow (little to no boost), yet the fuel is being used.
At the same 2000 rpm in the same gear going back up that hill in the other direction will use a bit more air, but a much greater percentage increase in the fuel.

Your own recognition that closed throttle engine braking, a condition that uses no fuel, shows a faster rate of fuel use than neutral, a condition that DOES use some fuel to maintain idle rpm, obviously indicates that the meter is incapable of determining even relative fuel use increases or reductions from which a "better or worse" comparison can be made.

 

[Lug_Nut]

This is from Ultragauge's own site.

http://www.ultra-gauge.com/customer_support/knowledgebase.php?article=27

Really no different than the PLX Kiwi MPG I tried.
It could be calibrated based on the average of the prior tank full, but unless you drive exactly that same way for the new tank the accuracy isn't that good.
And minute by minute fuel use? totally useless in a diesel.

 

[john.jackson9213]

What you do is set the nozzle on low and after it shuts off, you slowly keep adding fuel. It will foam some so what you do is let the bubbles dissipate and slowly fuel some more.

After a few times of doing this, you will end up with clear fuel just shy of spilling over the filler neck. Extremely accurate, and only takes a couple of more minutes to do.

Pen and paper calculations are the only accurate way to calibrate what ScanGage is telling you.

I think the method for calculating MPG described in post #6 would be accurate, as well, but still pen and paper.

I have used this method to top off the tank ever since I vented the tank. But with the wagon, I have to add around 8 gallons of D2 at very low fill rates. Usually takes between 5 and 10 minutes to get the last 8 gallons in the tank. Then pen and paper to calculate MPG.
Now that I am using Propel HPR fuel, topping off the tank is quicker. The fuel is way less foamy, so I can put the last 6 or 8 gallons in at a faster flow rate.

 

[thechoochlyman]

Finally managed to score a scangauge on eBay for relatively cheap, so we'll see what kinda MPG improvements I can get.

2. Once you're sure of your mileage, calibrate said Scangauge. You calibrate it by changing the gas tank size, and the liter engine size. I haven't messed with diesel a, and diesel b, but you might monkey with those too. Between the first two presets though, I've been able to dial my scangauge in pretty well.

For instance: on my old b4v I set my fuel tank size at 27 gallons, and had the engine size at 2.0 liters (it was tuned/injectors/etc). This got me to within 5 miles over a 10 gallon tank. Not too shabby.
My new b4v is set at 25 gallons for the tank and the 1.9 liters, and so far it pencils out to within 10 miles per 10 gallons. Again, pretty good.

So just out of curiosity, how does the engine displacement and tank size affect the MPG reading apart from filling up the tank and telling it how many gallons it took, according to the manual?

 

[PD41]

Hook up a Floscan. They use them on boats. Connects to the fuel line and gives you gallons per hour. Then you can adjust your RPMs and see the consumption change live.
http://www.floscan.com/html/blue/custompages.php?pageid=62

 

[Steve Addy]

Finally managed to score a scangauge on eBay for relatively cheap, so we'll see what kinda MPG improvements I can get.

So just out of curiosity, how does the engine displacement and tank size affect the MPG reading apart from filling up the tank and telling it how many gallons it took, according to the manual?

I too would like to know how the thing works. I have followed what the manual says about filling / pricing but the mpg function doesn't report properly. First it was way over what it should be then I reset everything and now it sticks around 1.4 all the time. I just ignore it now really.

I did figure out how to adjust the speed so it reports accurately and consistently with GPS.

Steve

 

[thechoochlyman]

I actually just got my ScanGauge II delivered and installed yesterday. I really love it so far, the interface is very easy to use and read. Plus the fact that it's made in the USA really impressed me.

I set it to Kilometers per hour and synced the speed with my GPS, as other had suggested. Had to go +2% on my worn, stock-diameter tires. I'm currently displaying MPG, MPH, RPM, and voltage. Only put on the RPM to find my best engine speed MPG.

The MPG is showing way too favorably in the positive - the trip estimator showed 68 MPG driving to work this morning. My parameters are set to 1.9 liter engine, 21 gallon tank, and Diesel A. Hopefully it'll get closer to actual once I fill it up two or three times.

 

[thechoochlyman]

I too would like to know how the thing works. I have followed what the manual says about filling / pricing but the mpg function doesn't report properly. First it was way over what it should be then I reset everything and now it sticks around 1.4 all the time. I just ignore it now really.
I did figure out how to adjust the speed so it reports accurately and consistently with GPS.
Steve

It probably defaulted to settings for a gas car whenever you reset it. And no telling what engine size it thinks it has.

I can see how altering the engine displacement would make the "baseline" MPG more accurate. I can also see how this would be the preferred way to calibrate your scangauge, because you can write these settings down and re-input them any time you want to. (For instance, if you wanted to move your scangauge to another vehicle for a while, you wouldn't have to go back through the tedious fillup process all over again.)
I'm still uncertain as to how you'd go about adjusting your displacement to match fuel consumption. Although I'd imagine it's something like:

1. Fill up your tank
2. Drive to empty
3. Fill back up and calculate MPG with pen and paper
4. Compare your scangauge average tank MPG to your own calculated MPG
5. Adjust engine displacement until stored tank average MPG matches what you calculated.

This is, assuming that changing a stored value will alter all the trip values to match.

But I don't see any reason for altering the tank size apart from getting a more accurate distance-to-empty reading, which I don't really need.

 

[ToddA1]

Ummm, yes and no. There is still fuel being moved to and from the tank and recirculated within the pump, but none is injected for combustion.

I've never quite wrapped my head around this part. Is the engine actually running, or is it off and rotating (while all sensors are live) since it's connected to the driveline?

-Todd

 

[thechoochlyman]

I've never quite wrapped my head around this part. Is the engine actually running, or is it off and rotating (while all sensors are live) since it's connected to the driveline?
-Todd

Here's what the scangauge told me this morning:

Coasting downhill in gear, cruise off - ~3,000 MPG, .02 GPH

Coasting downhill in neutral - ~1,000 MPG, .06-.07 GPH

In neutral sitting still it shows a consumption of .07 GPH.

This seems to support what LugNut was saying, although it still shows a very slight consumption of .02 GPH and not zero entirely.

 

[Windex]

I found that the SGII in my B4 was accurate, once I had put a couple tanks through, and adjusted it to my liking.

The only thing that would then make it inaccurate is if my driving changed significantly.

If I would continue to drive my normal highway commute, the L/100 instant, tank and trip x gauges were quite accurate.

If I had to do a tank of mostly city, It would not be as accurate.

I set mine to 2.0L, Diesel A, and 25 gallon tank (wagon).