ScanGauge II Questions

[tom1l21]

I have a couple scangauge II (xgauge version) questions.

1. I have seen some threads about the optimal RPM's, and the consensus I gathered was that at 2000RPM's, the ICE is achieving its best fuel efficiency. Is this true, if not what should the target RPM's be?

2. Sometimes when I accelerate, the RPM's jump down from 2000 to 1000. Is this simply the ICE lowering its RPM's before it uses an assist from MG2?

3. I have an xgauge set for the fuel economy for a current trip (displays the MPG for the current trip). Sometimes, I will turn my Prius off and like usual, several seconds later the scanguage will turn off. If I come back to my Prius say, 2 mins later, and turn it on, it will still record the data from the previous trip. It has to be a considerable amount of time (not sure the exact number) before it will reset the data from the previous trip to make way for the current trip's information. Does anyone know the time that this usually is?

4. If you enter in the wrong fuel information (# of gallons or incorrect +/-%) when you fill up, are you pretty much SOL until the next time you fill up?

I have a couple more, but just can't think of them right now. Any information though would be greatly appreciated. Thank you!

[mlupan]

I can answer #3. I think it is 8-10 hours. It is printed in the owners manual.

[tom1l21]

Originally Posted by mlupan

I can answer #3. I think it is 8-10 hours. It is printed in the owners manual.

That code is one of the pre programmed codes (CFE) I think and that is your fuel efficiency for the day and is reset after 8-10 hours which would presumably be the time one comes home from a work day to when they wake up in the morning. The xgauge I programmed by using the instruction manual codes is the fuel efficiency for each trip. It seems that I have to wait about an hour or so after turning of my Prius for the "trip" data to reset. It could be 20 mins instead of an hour, I'm not sure. That is what I am curious on.

[JimboK]

1) I keep RPM as low as possible while still keeping the ICE under load, sometimes as low as 1200-1300 even under (low-speed) acceleration. Since you're doing X-gauges, see this for a discussion on using an X-gauge for fuel injector timing as an indirect indicator of ICE load.

2) Not sure why the sudden drop in RPM while accelerating. What's the vehicle speed, how quickly are you accelerating, and what's your SOC? Above 40 MPH, ICE-off conditions still involve the ICE spinning with no fuel flow at about 980 RPM. A sudden dropoff to that level is common under light load conditions. But I can't see it doing it under conditions that require 2000 RPM except possibly with a very high SOC where the car decides on its own to go suddenly into electric-only propulsion.

[wintechsw]

Originally Posted by tom1l21

I have a couple scangauge II (xgauge version) questions.


I have a couple more, but just can't think of them right now. Any information though would be greatly appreciated. Thank you!

My observations for highway cruising are:

1. On Cruise Control on a flat road, the RPM can vary +/- 300rpm with no discernable variation in ICE noise so I don't think it is measuring just engine rpm.

2. The sweet spot for best speed/good consumption seems to be a LOD figure of 78. Anything over that takes my consumption over 5l/100km (sorry about the metric measurements in Oz). I've found also that keeping the cruising speed at 106kph on the speedo keeps the RPM figure < 2000rpm which keeps the LOD below 78.

3. Around urban areas I try to keep IGN at 14 and TPS at 18 for really good consumption figures. It takes a bit of doing depending on the road/driving conditions but it pays off.

4. I suggest you set up Soc(State of charge) on your SGII as it explains a whole lot of what goes on in the car and why various things are happening(see attachment).

HTH

[JimboK]

Originally Posted by wintechsw

1. On Cruise Control on a flat road, the RPM can vary +/- 300rpm with no discernable variation in ICE noise so I don't think it is measuring just engine rpm.

Not sure what you're suggesting when you say "it" is not measuring just engine RPM. What is "it"? ScanGauge? If so, are you saying that the RPM gauge somehow is a composite of multiple parameters? How could that be?

Anyway, I too see RPM floating up and down by several hundred RPM without much noticeable change in ICE noise. That's the nature of the beast.

Originally Posted by wintechsw

2. The sweet spot for best speed/good consumption seems to be a LOD figure of 78.

Some use LOD as a sweet spot indicator, but the number of 78 won't work for Tom and his '05. Some of us have compared our LOD readings in the '05 with others in later models. Later models consistently are significantly higher for a given combination of driving conditions, speed and ICE RPM primarily. For me, the LOD sweet spot range is in the 40s to low 50s. See this for more, where discussion on this issue begins at post 14. Best guess is that for either the 2006 or 2007 model year (I can't remember now when a change first showed up), Toyota changed the way the car calculates and reports LOD.

[tom1l21]

I read some info on the xgauge injector timing and it seems that the consensus for best fuel efficiency was a timing value of 5-6. Is this really true for P&G speeds, or any speed alltogether? At those values, I see around 1300RPM which for me is a pretty slow acceleration compared to the 2000RPM acceleration I previously used.

[JimboK]

Originally Posted by tom1l21

I read some info on the xgauge injector timing and it seems that the consensus for best fuel efficiency was a timing value of 5-6. Is this really true for P&G speeds, or any speed alltogether? At those values, I see around 1300RPM which for me is a pretty slow acceleration compared to the 2000RPM acceleration I previously used.

I use that range pretty much for all ICE-on conditions when traffic and road conditions allow. At slow speeds on level terrain, it results in acceleration. That's fine, given my extensive use of P&G. ICE RPM indeed can be in the 1200-1300 range. At higher speeds it ends up being steady-state, with RPM generally around 1400-1600, depending on speed.

[tom1l21]

Originally Posted by JimboK

I use that range pretty much for all ICE-on conditions when traffic and road conditions allow. At slow speeds on level terrain, it results in acceleration. That's fine, given my extensive use of P&G. ICE RPM indeed can be in the 1200-1300 range. At higher speeds it ends up being steady-state, with RPM generally around 1400-1600, depending on speed.

Isn't this a bit contradictory to the whole "keep iMPG to 1/2 the speed"? At 1300 RPM, I almost see the two values being the same. The acceleration while at 1300 RPM is what I would call "crawling" compared to the term usually thrown around as "brisk" for P&G. Is there possibly something wrong with my Prius that would cause its lack of torque? Engine air filter is very clean.

On another note, I read somewhere (might have been from you Jimbo) that the optimal current for recharging the battery is 60 amps when using regenerative braking. Is this correct, and is there any evidence to prove it? Thanks.

[JimboK]

Originally Posted by tom1l21

Isn't this a bit contradictory to the whole "keep iMPG to 1/2 the speed"? At 1300 RPM, I almost see the two values being the same. The acceleration while at 1300 RPM is what I would call "crawling" compared to the term usually thrown around as "brisk" for P&G. Is there possibly something wrong with my Prius that would cause its lack of torque? Engine air filter is very clean.

On another note, I read somewhere (might have been from you Jimbo) that the optimal current for recharging the battery is 60 amps when using regenerative braking. Is this correct, and is there any evidence to prove it? Thanks.

The iMPG to 1/2 MPH rule is what I recommend as a maximum for acceleration, not necessarily a constant target. It pretty consistently produces ICE RPM in the 2200-2400 range across a wide range of speeds. Above that and most everyone seems to agree you're getting into substantially greater ICE inefficiency. See this for more. As you get to the end you'll see where I've gradually evolved to thinking low RPM ranges are OK as long as the ICE is under load. And you'll also read where I explain why I don't care for subjective terms like "brisk" or "gentle" to describe acceleration.

And yes, 1300 RPM would be considered by many to be rather slow acceleration, and by a few, crawling. There's nothing wrong with your car in that regard.

As for braking, that number didn't come from me, and I'm not sure where it came from. Attila Vass, one of the early researchers and CAN-hackers on the Prius II, found in testing that a brake pedal position of 17 as reported by CAN was the most efficient for regeneration. I don't know what that translates to in current flow, but it's about what it takes to slow the car from 45 MPH to 5 MPH in 22 seconds. Frankly, I don't worry too much about efficient braking because any braking is less efficient than not braking. In my hypermiling approach I avoid the brakes as much as possible.