Is the gas engine really on?

[rioman]

I bought a ScanGauge II a few mos. back and noticed that frequently the RPMs in the Gauge display are just under 1000 and yet the Energy display in the center console shows the engine is turned off because I am coasting and not depressing the gas pedal.

Is the RPM measurand on the ScanGauge displaying the engine RPM and if so is it just running for lubrication, but there is no combustion occuring, as indicated by the Energy display

[patsparks]

The centre console or MFD shows you are not using any petrol, it doesn't show engine revs. If you are doing more than 42mph the smaller electric motor spins the engine to prevent the smaller electric motor over-speeding.

In a conventional ICE car it is possible to have a zero fuel situation because the injectors sometimes don't inject any fuel in a high manifold vacuum situation like going down a hill on a closed throttle.

[archae86]

Since I first drove the Prius I noticed that on stopping at a stoplight at on a multi-mile downhill, the car gave a little shake a few seconds after stopping that seemed very like the likely feel of the gasoline engine stopping. This despite the fact that the engine icon had not been on for many seconds.

Sure enough, my Scangauge 2 shows the rpm dropping from somewhere near 1000 to zero just on that shake.

So on this point, as on several others, I think the SG2 is telling the truth and the Prius display is false (or, to be more charitable, oversimplified).

I'll watch fuel flow rate and rpm through this sequence to verify that the engine is using fuel during at least the last few seconds of this sequence and report, but I'm quite confident that it is.

[V8Cobrakid]

I think you're mistaking the car trying to burn off extra electricity from the long downhill with the ICE actually running.

It's not running. the Car tends to "seat" the ice into a proper startup point.. and sometimes idles it with electric motors only to burn off excess electricity.

From everything i've read on here.. there are only a few cases where the ICE idles... heavy A/C use and the Defroster... along with engine warmups.

[icarus]

Above ~41mph the ICE will continue to turn at ~980 rpm. The injectors and the ignition are off, as it is only serving to govern the electric motor. When the car "shakes" at a light for example, the ICE is stopping completely, confirmed by the scan gauge. The MFD is only over simplified when it shows the ICE not running when it is still turning, but using no fuel.

Icarus

[patsparks]

V8Cobra Kid is right, if your battery is full, or displaying all green bars which can happen at the end of a long coast down hill then any excess electricity needs to be dumped. This is no worse than conventional brakes dumping heat as they always do. To dump excess electricity to avoid charging the battery beyond it's comfort zone of 80% the HSD uses the small electric motor to spin the petrol engine with no fuel injected then when it senses the battery is on 80% charged it stops causing a slight but noticeable shudder. It isn't burning any petrol.

Sometimes you might notice withing a few minutes of a cold start after you stop at a traffic light you feel the petrol engine give a similar shudder, this is actually the petrol engine shutting down as it finishes its warm up phase and enters its most economical phase. (stage 5 I believe) There is about a 1 second delay in the MFD but I believe it is accurate within that 1 second delay. At the end of the day it is the amount of fuel you use to travel whatever distance which really matters in a Prius. The Prius will return better numbers than any other mass produced car currently on the market.

[Bob64]

Originally Posted by rioman

I noticed that frequently the RPMs in the Gauge display are just under 1000 and yet the Energy display in the center console shows the engine is turned off because I am coasting and not depressing the gas pedal.

Your traveling at speeds above 41mph (or below 35mph) OR your not in stage 4 mode.

[qbee42]

Originally Posted by archae86

<snip> So on this point, as on several others, I think the SG2 is telling the truth and the Prius display is false (or, to be more charitable, oversimplified). <snip>

The MFD is not false. The screen you describe shows energy flow, not engine RPMs. The engine on the Prius often spins without burning fuel.

Tom

[Bill Merchant]

Conversely, I've noticed sometimes during start up that the MFD shows me moving on battery, with no arrows from the ICE, while at the same time showing 9 mpg rather than 99.9 mpg.

[andyprius]

Originally Posted by Bill Merchant

Conversely, I've noticed sometimes during start up that the MFD shows me moving on battery, with no arrows from the ICE, while at the same time showing 9 mpg rather than 99.9 mpg.

Related subject is "Stealth mode", Generally after 5 min warm-up and blue bar condition, Prius goes easily into stealth mode, at about 30-40mph. BUT, after a green charge is attained or faster speeds, (45-70mph), stealth is all but impossible to get. What is the, obviously very strict criteria governing Stealth mode???? AND if in many cases the ICE is only spinning and using no petrol, what is the advantage of stealth???