My new SGII is doing something I don't understand. I keep the instantaneous MPG displayed at all times, and I sometimes see it toggling between "9999" and a real mpg number (not related to going ICE off). This is easily repeatable on a long uphill near my home when the mpg is around 12.0, and will switch several times per minute to 9999 for several seconds. I'm not sure, but the 9999 may coincide with the mpg dropping into single digits (below 10.0mpg). Any ideas?

 

Probably your fuel cut setting is too high. It needs to be set to the TPS setting @idle +2 or 3. It is set to 24 by default but should be 14 or 15 for the FEH. You can set it to 0 to eliminate the feature altogether.

 

Thanks, I'll give that a try. I wasn't aware of that setting.

But does fuel cut come into play at low or at high fuel flow? I'm seeing this problem at very high fuel flow (12.0 mpg). Wouldn't fuel cut determine the threshold where low fuel flow becomes zero fuel flow (9999mpg)?

 

I wan't aware of this setting either, but not to ask a basic question, have you set the SG to Hybrid? I had to reset mine recently and I forgot to do this and it shut off completly during a long EV run.

 

Yes, mine is set to Hybrid. The problem I'm seeing is at high fuel flow rates (12mpg). I think the Hybrid setting is to keep the SG alive during EV.

I wondering if my problem is related to the SG "Rate" setting. I will try the slow and fast rates also to see if that helps.

 

It is related to the fuel cut setting.
What Carl didn't say is how it works.

The SG assumes ( does not actually measure ) fuel-cut mode when you have a low throttle position sensor reading and an open loop operating condition at the same time.
The FEH operates in "open loop" ( which means the fuel rate is NOT controlled by the oxygen sensors ) anytime you have a wide-open throttle condition ( also when you have a closed throttle ). This ( WOT ) happens frequently when accelerating quickly, and on hills. WOT does not mean you have your foot to the floor. This car is "drive by wire" plus it has a CVT. This means the car can be at wide open throttle at any time the computer wants ( based on driver inputs ).
The engine ( any engine ) is most power efficient at WOT so this is not a bad thing.
In fact, the FEH operates at just below WOT most of the time you drive at above idle. ( 87% open is very common ) The hill made your car go WOT and the SG saw an open loop condition occur. But you must have been going up the hill with light pedal pressure and the ScanGauge assumed incorrectly.

This is a limitation of the SG. You can choose if you most often have open-loop with true fuel cut ( 9999 MPG ) and leave this feature "on"... or, if you get too many erroneous assumptions, and you can turn it off like Carl described previously.

The confusing part is, the SG calls it "Throttle Position Sensor" but I think in our case, being "drive by wire" it is more related to pedal position. There is NOT a direct relationship between pedal position and throttle position. I really doubt you had the pedal 100% pressed, yet the car was at WOT. With open loop, and the pedal depressed below the level you set, the SG will assume fuel is cut off, and display 9999 MPG.

Does that make sense?
-John

 

Thanks John. Yes, that makes sense and fits my scenario. The hill where I see this is a highway hill where the ICE will hold 4000rpm to maintain 60mph, so it is likely to be WOT. I often feather the throttle on this hill to try to hold speed with reduced rpm, so possibly that is responsible for the light pedal pressure. I will adjust the fuel cut threshold and see what effect that has. Thanks for the great explanation!

 

Problem is fixed. I drove up that hill yesterday with the modified fuel cut threshold and the SG mpg reading stayed consistently accurate.

 

So, what did you change the fuel cut to? Somewhere between 13-16 I asume?

As far as the explanation, here's my version:

When you experienced fuel cut going up the hill with the default FC setting, you were most definitely not WOT. In fact, your throttle was obviously less than 24% (default TPS) open. The TPS is exactly as it sounds, the position of the throttle plate in the throttle body. It is not a indicator of the pedal position, that is another PID. And whether or not the vehicle is drive-by-wire is completely irrelevant. What matters is how much the butterfly is open, not how it got there. Open-loop fuel enrichment can and does happen at any TPS value, not just WOT. Ford seems to have chosen to make the $11 TPS PID represent absolute position, whereas some other manufacturers interpret it as relative. This is what makes determining fuel cut in this manner difficult for a generic tool. This despite the fact that relative position is defined by the $45 PID, although few cars support this PID. On the FEH, you can see that when the built-in TPS displays 12, the relative tps shows 0.

The FEH does not spend most of its time near WOT. If it did you would be pretty unhappy with its performance, both in terms of throttle response and fuel economy. It does, however, try to operate at fairly high engine load levels. Load as defined by the OBD-II specification (SAE J1979) is percent airflow relative to maximum possible. Again, this is open to interpretation and it seems like the FEH bakes volumetric efficiency into the $04 (LOD) PID. Without considering VE, the maximum airflow is given by the displacement times the RPM/2 for a 4-stroke ICE. You do not have to be at WOT to reach maximum airflow, although at higher RPMs you usually are.

 

Carl

My new '09 has a TPS of 14 while in "D" and Decel. I set my Fuel cut at 18, what do you recommend how I should measure idle TPS and adjust fuel cut?

GaryG