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Torque » Torque OBD ECU Scanner » Torque Discussion / Ideas » Yes.. another MPG question (255 MPG)

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Author	Topic: Yes.. another MPG question (255 MPG)

matt6575

Member
Posts: 8

Yes.. another MPG question (255 MPG)
on: June 27, 2014 (GMT)

I have a problem with the instant mpg when I let my foot off the gas and the car is in gear. It will jump to 255mpg and stay there till I press the pedal again. Now if I take the car out of gear and let my foot off the mpg reads more like I’d expect it to, 130 – 180 mpg depending on speed. What sensors is torque using to do the calculation? I’d like to display those to determine which one is creating the issue.

My vehicle: 1996 240SX (manual trans)
OBDII adapter: OBDLink MX
Enhanced MPG: enabled
Volumetric Efficiency setting: 65

1996 Nissan 240SX

frodus

Member
Posts: 518

Re: Yes.. another MPG question (255 MPG)
on: June 27, 2014 (GMT)

When you let your foot off, the MPG shoots way high because you’re using so little fuel, but still moving fairly quickly.

basically, its pretty much normal. Happens to me in my Audi A4.

matt6575

Member
Posts: 8

Re: Yes.. another MPG question (255 MPG)
on: June 27, 2014 (GMT)

Thanks for the reply.

I realize it will go up but even if I’m doing only 35mph it will jump to 255 meaning it could really mean 300, 400 or higher. Obviously at 35 I wouldn’t be able to travel more than 255 miles even at idle fuel consumption rates. It would take over 7hrs to go 255 miles at 35mph and I know my car would use more than 1 gal fuel in 7hrs at idle.

If I take my foot off and take the car out of gear and just coast it goes up but not to 255, more like around 100 – 130 at around 35mph or so. Which seems reasonable for the amount of time my car would idle on 1gal of fuel.

1996 Nissan 240SX

frodus

Member
Posts: 518

Re: Yes.. another MPG question (255 MPG)
on: June 27, 2014 (GMT)

Its likely that the value in the car only goes up to 255 as a max. It only went up to 200 or something IIRC on my car. Then it just blanks out my built-in MPG display with “–“.

Something to mention: Idle uses more gas than coasting, where you’re basically using the car to turn the engine, so little or no fuel is being used. In idle, there’s nothing turning the engine, so you do have a fuel supply. Idle will use more than coasting in some vehicles, depending on how their fuel injection mapping is set up.

matt6575

Member
Posts: 8

Re: Yes.. another MPG question (255 MPG)
on: June 27, 2014 (GMT)

hmmm I guess that could be. When I take it out of gear while doing 35 I guess the fuel system may be running in an “idle” mode and start consuming more fuel so it shows a lower mpg. It sounds counter intuitive to how you’d think it would work but I guess I could see this maybe being the case. I guess I could watch the fuel rate gauge and see how it is reacting.

I was also hoping to be pointed in the direction where I can find the actual PID’s torque is using to calculate the mpg when using enhanced mode. I’d just like to get a better idea of what my car is actually doing.

Also if you have fuel rate guage on the screen and you’re monitoring mpg as well is torque smart enough to only poll the sensor once even those it’s used for two displays?

Thanks for you help

1996 Nissan 240SX

matt6575

Member
Posts: 8

Re: Yes.. another MPG question (255 MPG)
on: June 29, 2014 (GMT)

So I watched what torque was reporting for “fuel rate/hr”. When I let my foot off the gas with car in gear the fuel rate drops completely to zero. I have a hard time believing my 1996 vehicle totally shuts off the fuel without any pedal applied, maybe I’m wrong.

I used the app that came with my OBDLink MX and it did not show the same behavior as torque did. The fuel rate never dropped to zero and I never got 255 or higher mpg reading with it.

How is torque getting it’s fuel rate readings?

1996 Nissan 240SX

matt6575

Member
Posts: 8

Re: Yes.. another MPG question (255 MPG)
on: June 30, 2014 (GMT)

Is there any info on how torque calculates “fuel rate/hr”? In torque the fuel rate drops to completely zero even looking at the gauge with 3 decimal places. However the OBDLink software that came with my adapter never shows the fuel rate dropping completely to zero.

1996 Nissan 240SX

anonyme0897

Member
Posts: 4

Re: Yes.. another MPG question (255 MPG)
on: September 17, 2014 (GMT)

It is completely normal for a 1990+ car to cut fuel supply when in gear and decelerating (no throttle). It is called DFCO (Deceleration Fuel Cut-Off). Search about it on google.

Depending on the car, fuel supply may be cut until engine speed has dropped to around 1000RPM. Fuel supply resume below that speed to avoid engine stall.

You can try it, it will be more obvious in a manual car. When going a decent speed (25mph or 40kmh), downshift in second gear and do not touch any pedal. You will feel a deceleration until around 1000RPM, then a little lurch forward.

matt6575

Member
Posts: 8

Re: Yes.. another MPG question (255 MPG)
on: September 17, 2014 (GMT)

Appreciate the feedback. I actually realized shortly after starting the thread that it was correct that the fuel was actually being cut off.

What really threw me off was the app that came with my OBDlink MX. It always reported fuel being used contrary to what Torque was showing. Obviously the other app was wrong. Guess I should have never doubted Torque.

1996 Nissan 240SX

NightFire

Member
Posts: 1

Re: Yes.. another MPG question (255 MPG)
on: September 21, 2014 (GMT)

I have the same thing happen with my 370x, Murano and Frontier.
If I coast in gear it reads 255mpg, no matter what speed I’m going. If I coast in neutral it shows different mpg, depending on my speed.

It seems like it’s a bug in torque. OBDLink never shows 255mpg.

anonyme0897

Member
Posts: 4

Re: Yes.. another MPG question (255 MPG)
on: September 21, 2014 (GMT)

Since there is no fuel burned at all when decelerating in gear (DFCO), it should read something like 9999mpg or infinite mpg. Torque doesn’t seem to be able to display over 255mpg though.

You could try to coast until the RPM drop a little below 1000 (where the fuel injection must resume). If the instant mpg display doesn’t drop from 255, then yes it is a bug.

MPD56

Member
Posts: 276

Re: Yes.. another MPG question (255 MPG)
on: September 21, 2014 (GMT)

Quote from anonyme0897 on September 21, 2014
Since there is no fuel burned at all when decelerating in gear (DFCO), it should read something like 9999mpg or infinite mpg. Torque doesn’t seem to be able to display over 255mpg though.

You could try to coast until the RPM drop a little below 1000 (where the fuel injection must resume). If the instant mpg display doesn’t drop from 255, then yes it is a bug.

MPD56: Reply

I’m guessing but if the ECM response is one byte for that PID then the maximum value would be 255. Zero to FF hexidecimal is zero to 255 decimal.
If the vehicle has shut off the fuel then what is the ECM suppose to show? Miles/fuel used =?

piemmm

Administrator
Posts: 6629

Re: Yes.. another MPG question (255 MPG)
on: September 22, 2014 (GMT)

Hi!

Whilst you’re in-gear and ‘idling’ (ie: decelerating slowly) then there’s no fuel used to keep the engine turning, it instead uses your momentum to keep the engine turning over

When you’re in neutral, you’re not connected to the wheels, so the ECU needs to use fuel to keep the engine turning over, otherwise the engine would stall. This is why you see fuel being used – it’s not a bug, it’s simply how your engine works

Torque at the moment is limited to 255MPG as the ‘max’ MPG (it would show infinite, but that confused quite a few people, so I instead imposed a max limit on it)

matt6575

Member
Posts: 8

Re: Yes.. another MPG question (255 MPG)
on: September 22, 2014 (GMT)

I understand now that the fuel does get cut off and why it shows 255mpg. However displaying 255 sounds like it would be more confusing. I’m guessing people were confused seeing an infinite display thinking it would somehow artificially inflate the average mpg calculation. Obviously this wouldn’t be the case. I’m sure the instant mpg has nothing to do with the actual average calculation.
I would much rather see it display infinite as that would technically be correct.

1996 Nissan 240SX

Xusn96

Member
Posts: 5

Re: Yes.. another MPG question (255 MPG)
on: December 17, 2014 (GMT)

Quote from admin on September 22, 2014
Hi!

Whilst you’re in-gear and ‘idling’ (ie: decelerating slowly) then there’s no fuel used to keep the engine turning, it instead uses your momentum to keep the engine turning over

Torque at the moment is limited to 255MPG as the ‘max’ MPG (it would show infinite, but that confused quite a few people, so I instead imposed a max limit on it)

Re: In a future release could this be changed to 999 or 9999 since infinity makes equations crazy. but would make the higher mileage coasting more accurate, albeit still limited. Or is this limit in place due to maximum code value from ECM?

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