Ultragauge MAF with diesel engine
 

Hi,

I have recently installed an Ultragauge to a Ford Focus diesel and I'm struggling with MAF, fuel cut-off and MPG readings. Basically when I coast in-gear zero throttle the Ultragauge inst MPG halves and the MAF doubles. This has the knock on effect of dragging down the average MPG.
I also have a Scangauge installed, which has been working fine for the last 6 months. When coasting in-gear zero throttle the Scangauge inst MPG goes to max of 9999.
Neither gauge shows open/closed loop and the Scangauge fuel cut-off is set to 0. From what I can find on the net, the Scangauge is using MAP to calculate MPG and the Ultragauge is using MAF.
I’m struggling to understand how the MAF can double, and double again when changing down a gear, when the car is coasting in-gear down a hill with zero throttle. A trip I do each weekend involves a 1.5mile steep hill and going by the Ultragauge it uses more fuel rolling down the hill than driving up it!
My simple logic suggests that the MAF reading when coasting in-gear zero throttle should be ignored by use of a fuel cut-off setting. The readings from the Ultragauge are fine at all other times. I have been advised that by not showing open/closed loop my diesel will not have a fuel cut-off feature.
I’m also wondering if the MAF sensor is giving a false output, however the car is driving without any issues, which leads me to think the engine management unit is programmed to ignore the MAF output when coasting in gear.

If anyone has any ideas or can help, it would be much appreciated.
Many thanks
Trefor

I'm in the same situation. 2007 tdci with ultragauge. Silly numbers off throttle in gear.

Being a diesel, fuel inputs are not dependent on throttle - it doesn't have a throttle. Then the turbo takes manifold pressure (MAP) another step away from indicating fuel used, compared to conventional petrol. Air flow (MAF) also not directly related to fuel used I would guess. The ECU must know how much fuel it's injecting - we get the trip fuel economy read out after all. But the ultragage seems not to be able to use that information from best I can tell. Shame, cause I'd like to know instantaneous fuel use, fuel used etc.

That's my best guess why it produces funny numbers some times (all the time??). I'll keep looking for a way round this.

Sounds like the UG interprets MAF as proportional to fuel consumption, which is not the case in a diesel. While cruising the engine computer will fuel according to the available air, but on decel the fuel will be cut back, but since there is no throttle, the air will still flow according to engine speed.

It sounds like you need a method to determine decel, even the Scangauge is very inaccurate on diesels with a lot of DFCO.