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Just got my SGII a couple of days ago and noticed that RPM shows a value sometimes when the MFD shows no ICE running. And it's not just lag time in the refresh - it has done this several times.

Also: Why is RPM a negative # during first minute warm up?

What am I looking to achieve for a LOD value?

I have been reading a lot of posts but don't yet have a full understanding of how each value is related. For example I know that RPM is most efficient between 1500-2300, then why does IGN 14 appear when RPM is <1500?

Please forgive me if these are dumb questions - I must be missing some basic concepts that I need to learn. Where is the hypermiling for dummies book?:D

Hi Neicy:

___The MFD is wrong in some instances unfortunately :( Especially during warm-up or if you have not performed that darn idle check after S4 is reached :angry:

___I do not remember seeing a negative RPM during warm-up???

___LOD … The Prius apparently tries to run the 1.5 loaded up in the 70 – 90% range w/ the variable valve timing tricks most of the time so I let that parameter fall off my radar screen when behind a Prius’ windscreen.

___About RPM’s … I do not believe that the Prius is most efficient between 1700 and 2300 RPM. My best highway numbers came about between 1150 and 1380 RPM albeit at speeds below 57 mph.

___Do not worry about the questions as they are good for both you and others that follow.

___Good Luck

___Wayne

Hi, Neicy. Piggybacking onto Wayne's comments.

One common scenario when SG shows an RPM value in ICE-off conditions is during coasting or "warp stealth" above 40 MPH. The engine actually is spinning around 980 RPM or so, but with no fuel flow.

I am just about convinced that what he says about efficient RPM values is true. I have recently reduced my RPM to sub-1500 numbers whenever possible, both during pulses and sustained speeds. I'm getting MPG results now as good or better than any I've ever achieved. For sustained driving on flat or downhill terrain, I'm keeping them as low as I possibly can with the ICE still running, generally about 1175-1200.

I think you'll find that RPM is the most valuable SG parameter to measure. You could try some of the others like IGN, LOD, or TPS, but I would learn their relationship to RPM and use them mainly as RPM surrogates. You might find them a tad easier to monitor than RPM, as their values don't bounce around as much.

I too question negative RPM numbers. Never seen that, never heard it reported, and it shouldn't happen. The ICE spins only one way. :confused:

I don't know about negative rpm's but the IGN will usually run from -10* to -11* during warm-up. I think this is to help warm the cat up since firing the plug that far after TDC would almost have to mean that raw fuel would be getting to the cat to help warm it up faster.

So in other words the MFD sometimes lies - which makes sense because I could have sworn I heard the ICE running with no arrows coming from it on the MFD. Thanks for the feedback. Maybe what I am interpreting as negative RPM is not really negative RPM. It appears , for example, as "1280RPM- " when I first start the car, and later it may be " 1280RPM " I think maybe I will replace LOD with MPG so I have that in the same place. I was reading that it is easier to hold IGN than RPM in the other posts, so I will keep that for a while and watch it more.

JimboK, that's what I thought since it was paired with an IGN value of 5. I did notice that maintaining speed on the HWY today was easy around 1180 RPM or so, and with good MPG.

The good news is I am sitting at 58.x mpg - but just filled the tank so that can change in a heartbeat right now. That's compared to 52.2 on my last tank. My short weekday commutes kill it.

Thanks Wayne, Jim, and diamondlarry.