This info came from a question Wayne Gerdes asked in my presence. You can contact him for more info and a confirmation that fuel is cut during L gear engine run-up. He was really into fuel-cut questions at the time. During the engine run-ups Gary speaks about, the SG always shows more fuel consumption, while the onboard Navi always shows maximum fuel economy.

P.S.
Taking the hint of using the metric system:
Tonite I went down a steep hill at about 50 MPH.
I shifted to L and took my foot off the gas.
Engine ramped up to ~4000 RPM.
I pressed reset on the Navi fuel screen.
After more than half a mile of 4000 RPM engine speed, the total fuel consumption was exactly 0.0L / 100km.
0.0L / 100km is exactly what it shows in EV mode as well.

 

YES!

During L gear engine run-up the car does go into open loop.

Also:

TPS: Throttle Position Sensor EV = 12
TPS: Throttle Position Sensor L gear run-up = 12

I've never ever seen it less than 12.
Coasting in D it is at 14.
-John

 

GaryG — I don't know why SG reports incorrect LOD readings. My understanding from Ron DeLong is that the LOD figure is supplied directly on the CAN bus, and isn't computed by SG from other data. The fuel-cut difficulty for SG is apparently due to the fact that Toyota hybrids continue to provide data on the CAN bus that implies that the fuel injectors are still squirting, even though it's not so! Perhaps likewise meaningless LOD data are still provided on the CAN bus during fuel-cut.

The TCH uses two planetary gear sets. The first is the "power-split device" and the second (which has one of its three inputs "grounded") is simply used as a fixed reduction gear for MG2, to increase the latter's torque by letting it spin faster relative to the wheels. The reason for spinning the ICE at speeds above 64 km/h is because MG1's rotation speed can get dangerously high when the ICE isn't turning. Presumably, choosing 64 km/h leaves an acceptable margin of safety — I don't know how conservatively Toyota have chosen this number. The THH has a third MG on the rear wheels, and the gearing of the drive train is probably different. I'm not knowledeable enough about this model to give a more meaningful comment.

gpsman1 — Your SG data are both interesting and meaningful! In my TCH I find that when the ICE is off and the car is stationary, the TPS is ~18 (as I recall — I'll have to check this). When driving, I've seen it fall as low as 13, I think. These numbers are comparable to what you've found in the FEH. [I understand, however, that there's no standardization between manufacturers as regards the range over which TPS varies.] I'll have a look to see what it does when fuel-cut mode is in effect. Using SG to see directly what the fuel usage rate is at any time is valuable too (in L/h or galUS/h). This number is, however, quite wrong during fuel-cut, for the reasons outlined above.

Stan

 

Okay, here is what I found with my TCH. When the car is cold (e.g., first thing in the morning), SG gives the TPS as 18. (I have no reason to doubt SG's TPS readings.) When the ICE starts up, the TPS rises to 19 and then gradually decreases to 16 as the engine idles. It stays between 15 and 16 when the engine is warm and idling. Coasting with the ICE "on" and using fuel, the TPS reads 15. Coasting in fuel-cut mode (no fuel usage, but the ICE is spinning), the TPS reading is 15 in either the 'D' or 'B' gear-shift positions. Coasting in pure-EV mode (ICE not spinning) the TPS reading is 14.

Stan

 

I spoke too soon. The SG does not always read TPS 12 when in fuel cut.
Trying it more today, I saw TPS 13 in Open Loop and also as high as TPS 22 in Open Loop.

Almost like it "freezes" in the last spot right before the Open Loop / fuel cut.
Maybe the SG stops getting TPS data all together in this mode and only the last frame of data received is displayed?

That time I had TPS 12 in open loop mode may have been just moments before an ICE shutdown, and that frame of data got frozen on the display right before the car decided to do engine brake instead.

It for sure always shows open loop each time the engine ramps up for engine brake.

To clarify the terms as Ford uses them:

"Open Loop: An operating condition based on instructions not modified by PCM feedback."

"Closed Loop: An operating condition or mode which enables operation based on sensor feedback."

 

gpsman1 — I find the same "frozen" behavior with my TCH. I think that they leave the throttle vane in the same position it was in at the instant that fuel-cut was invoked (the ICE was idling). I'm pretty sure that correct TPS data are provided on the CAN bus (and thus read by SG) even during fuel-cut. It would seem, however, best to place the throttle vane in that position that would be optimal for the desired engine braking effect. By leaving it almost completely closed, they do increase pumping losses. It also means that it's in the correct position to put the ICE back into idle mode when fuel injection is resumed, and I'd guess that this is why they do it.

Stan

 

Just learned three more things:

A) The FEH goes open loop at Wide Open Throttle. ( I think this may be in a technical service manual, but I proved it true today. )

B) The FEH will also run Fuel Cut in Drive, when coasting.

C) The FEH will NOT do Fuel Cut in Neutral, when coasting.

-John

 

I took a road trip today and made some observations that might be of interest. The return trip involved an extended downhill run (15+ miles) at coasting speeds a little over 40mph. Temperature was about 60 F. I believe the battery was fully charged as I could not feel any regenerative braking, and the engine would rev to about 3300rpm in low to slow the car.

What I observed was the following approximate mpg's under the conditions noted. The numbers are only approximate but might indicated if the injectors are shut off.

Downhill in Drive (45mph) 75mpg (1500rpm)
Shift to Low (45mph) 35mpg (engined revs to 3300rpm)
Shift to Neutral (45mph) 100+ mpg
Shift back to Drive from Neutral (45mph) 100+ mpg (no observed mpg change from Neutral)
Shift back to Low from Drive (45mph) 35mpg (engined revs to 3300rpm)

It looks to me like gas is being burned when coasting in Drive, and more gas is being burned in Low due to the higher rpm.

Less gas is being burned when coasting in neutral, possibly the injectors are shut off. But the gas consumption stays low when returning to Drive from Neutral, as if the injectors shut off and stayed off. Going back to Low causes the fuel consumption to increase as before.

Don't know what conclusions to draw, but it's repeatable as I had plenty of time to run up and down the gears while watching the ScanGauge.

 

This is where the ScanGuage is in error.
The Scanguage DOES NOT get the signal that fuel is cut, and assumes fuel is being burned, when it is not.

Do this next time.
Use the Metric System in your built-in fuel economy system.
In the conditions you describe, especially L gear, your Instant fuel economy will read 0.0L / 100km.

I just coasted down a 7% grade in Drive at 65 MPH for more than 10 miles, and after 10 miles I had used exactly 0.0L on the built-in.

After 48 miles, the built-in said 3.3L / 100km which equals 71.3 MPG.
After those same 48 miles, the SG said 56.2 MPG, which was WRONG.

Further evidence is, on that long downhill coast in Drive, my water temperature went from 186'F to 138'F in just a few minutes.
And I have my radiator still blocked with cardboard for winter!
A cold engine supports no fuel being used.

Now coasting in L gear almost always = 0.0L being burned.
Coasting downgrade sometimes = 0.0L being burned.
Coasting downgrade in N never = 0.0L being burned.
In N coasting, mine reads about 1.3L / 100km which is about 196 MPG.

Using the metric system is a way to get your built-in or Navi to go up to 2350 MPG. 0.1L / 100km is about 2350 MPG!!!

0.0 L = EV mode or fuel cut mode
0.5 L = 470 MPG
1.0 L = 235 MPG
1.5 L = 156 MPG
2.0 L = 117 MPG
2.5 L = 94.1 MPG
3.0 L = 78.4 MPG
3.5 L = 71.3 MPG
4.0 L = 58.8 MPG

This GARYG, is how I fugured out fuel-cut modes.

More later... gotta get to work.

 

gpsman1 — Your observations on the FEH are, I think, in complete agreement with mine on the TCH. And, yes, using metric FE is the best way to monitor fuel usage, since the L/100 km number relates directly to the amount of fuel consumed. FE in mpg is in an inverse relationship to fuel usage, and this makes it more difficult to understand what's going on. In the metric (Canadian) TCH the FE gauge reads in L/100 km, and when it reads 0 it means zero fuel usage, as I've reported earlier in this thread.

econoline — From your observations, it sounds to me as if the FEH behaves just like the TCH when you put it into Neutral while coasting: it starts up the ICE in order to prevent MG1 from over-revving. Since in N it can't power MG1, this is the only available option for protecting MG1, apart from actuating the disconnect between the drive train and the wheels.

Stan