Bafflingbs

sptmylstbreath

Do you have a source for this and your A/F ratio comment? Why would pulsations, if the fuel pressure is monitored and sampled at a high rate with a pressure transducer, affect your calculation?

Do you know what ford is using to measure fuel consumption?

Ricktwuhk

Today I put almost 29 gallons in my truck and the truck said I had gotten 16.8mpg. My hand calc came up with 16.75, so I filed a complaint with Ford and the NHSA. I cannot accept accuracy of 0.2976%.

11screw50

I have a much different theory (that is probably not even close but...).

Mine is much more accurate in the summer than in the winter (even when I do not use remote start). The truck also runs rich until it is warm. I postulate that the gallons used is based off the fuel table and that it only references the table used when the engine is at operating temperature, ignoring whatever adds fuel when the engine is cold.

Probably way out in left field but I figure it's as good a theory as I've seen.

fsae150

Sorry, wasn't paying attention when I posted earlier and I thought you were talking about an individual trying to calculate fuel flow based off IDCs and fuel rail pressure recorded from a obd II dongle, not the PCM calculations. That is more difficult because you don't necessarily know all of the injector characterization, such as flow curves, latency, etc., and even though the PCM calculates all of this very rapidly internally, it is computationally expensive to send it out to the rest of the CMs, so the values reported to the obd II network are nut updated as frequently as the internal calculations. However, yes, the fuel flow rate is calculated by the PCM fairly accurately, but in the reverse order of what you said. The PCM measures or estimates air flow first, then calculates the required fuel flow to achieve a target AFR and then calculates injector duty cycles required to achieve this. There are a lot of sources of error here, such as system dynamics and injector flow variation, so there are additional fuel trims applied to make sure the target AFR is actually achieved.

Fuel rail pulsations can still make an impact on fuel delivery because even though you can measure FRP at high speed, it is only measured at one spot. You get waves travelling through the fuel rail as a result of not only the fuel pump and various control valves, but also injector opening and closing, which can cause fuel pressure to fluctuate at each injector. Additionally, if you are running WOT, you can run into the issue of injectors flowing so much fuel that some injectors (especially the injectors furthest from the rail inlet) can run out of fuel. All of these issues make it very difficult for the lamen to calculate fuel flow rate based on IDCs and FRP, and you would be much better off using AFR and air flow to back out fuel flow. When real fuel flow rate measurements are required, like doing engine development work on a dyno, a fuel flow meter is installed.

I'm not sure exactly what Ford does to calculate MPG in our trucks.

Haha sorry to the OP for getting this thread so sideways!

Mach 1

If you are looking for accuracy in fuel economy...

It starts with consistantcies...fuel station/fuel pump calibration, fill technique, fuel specific gravity, and ambient temperature are some more on the list.

We have to use at least a 5 tank roving average as well to minimize out lying points. I use a lifetime average as well.

What a lot of drivers don't understand is, fuel economy monitoring is a very important diagnostic procedure. And it doesn't have to be as scientific as I let on to be.

How you say? If there is a difference or out of the norm fuel economy reading then this should be your red flag telling you something has changed. If nothing else, this is also a time ticker showing you that this is the time where something changed. Key important part of diagnostic work is when did you notice it changed.

What I always see is when the fuel station is using winter blend, cause my vehicles take a good hit. Some years here in Texas we don't even see it happen. Keeps me on my toes..

aspade

I logged 20 consecutive tanks, 568 gallons. The average error was +/-0.4% and only 4 tanks were off by as much as 2.0%. That's plenty precise in my book.

The problem is that that precision is dancing around a zero point that's 7.3% high and can't be corrected. And they all do it.

Ford programmed these to read high and impress customers on the test drive. That's all there is to it.

motsco

does anyone think about evaporation or how much alcohol is in the gas you purchase?

if you can find the owner of the place you purchase your gas from and ask him about what the oil industry calls shrinkage.

tanker can be loaded at terminal and can be 25 or more gallons less when it reaches it drop off point.

now let's talk alcohol in the fuel. got a lawn mower or any carburetor run yard machine? ever had on sit for a month and not start? have you been told carburetor needs to be replaced?

take a a look at how alcohol and water reacts.

Gulleyrw

Noticed on my 2016 XL Sport 4X4 SCrew that Ford changed the trip display from my 2011 and no longer shows the gallons used.

This location now shows DTE instead.

I cannot find that gallons used is listed in any of my options. Not a fan as the DTE is already in other places in needed.

Anyway to change this am I missing where this was moved to.

msgtord

Same change to the 2017 Super Duty. Fleet owners are not happy.