Scangauge II fuel cut off seems to work very well

[Right Lane Cruiser]

Thanks -- I'm aware of its uses but my car does not have this feature. I mentioned the after pulse behavior because what I saw was an odd fluctuation in instantaneous consistent with the ScanGauge thinking I was in fuel cut. I adjusted the feature to never activate and it went away.

What I saw was a kick to 9999mpg right after finishing the pulse and dropping to neutral. This was at peak RPM. The instantaneous would then drop to something reasonable as the tachometer needle descended... until it got close to idle. At that point it would again kick to 9999mpg briefly before returning to what it should show at idle for the speed. With the feature turned off, I see the numbers blip up a bit at those points, but not all the way to 9999mpg.

Coasting down in gear nets me only a few more mpg over steady state cruising because I lack fuel cut.

[-mr. bill]

Disagree that fuel cut only works while in gear!

After a pulse to say 3000 RPM, totally remove foot from accelerator pedal, push in the clutch or put it in neutral you *WILL* get a brief fuel cutoff until RPM drops to ~1000 RPM. Your engine is using the momentum of the flywheel to keep turning.

In a manual transmission car, you save a wee bit of fuel with each upshift because of this!

-mr. bill

[mtbiker278]

True that the flywheel will keep the engine turning over for a short period of time that could give you the criteria needed for the fuel cutoff. However, the gains from such a short period are fairly minimal, but not to be over looked. The most fuel efficient method of using the fuel cut-off is to coast down in the highest gear possible for your speed.

[Shrek]

Originally Posted by -mr. bill

Disagree that fuel cut only works while in gear!

After a pulse to say 3000 RPM, totally remove foot from accelerator pedal, push in the clutch or put it in neutral you *WILL* get a brief fuel cutoff until RPM drops to ~1000 RPM. Your engine is using the momentum of the flywheel to keep turning.

In a manual transmission car, you save a wee bit of fuel with each upshift because of this!

-mr. bill

Interesting. I do see this behaviour on the SG, but not on the iFCD of the car. I think the iFCD has a filter to avoid showing this behaviour (probably so as to not worry the not-so-technical drivers and have them running to the dealer with questions)

[2way]

Does the Fuel Cutoff in the SGII effect its MPG calcs? I know that even in cutoff, my ICE uses a minimal amount of fuel.

[-mr. bill]

Well, I'm upgrading my SGII to the new firmware next week, but trust me, without fuel cutoff detection, you can get fairly high wrong GPH values at >7,000 RPM no throttle.

-mr. bill

[pumaman]

OK, I'm still trying to wrap my mind around this fuel cutoff idea. Since I've started hypermiling I've just been trying to be in neutral as often as possible because I thought that was the best way to save fuel. I was willing to sacrifice the additional wear on my brakes. This complicates things. So....

In a MT car with fuel cutoff, if you're gliding in gear and cutoff is activated, you aren't using fuel and the engine is still spinning and still powering the power steering/brakes etc. right? So then if you push in the clutch at this point without touching the gas, disconnecting the engine from the transmission and wheels, you're saying the engine automatically restarts so it can idle and provide power while you're in neutral? I would think you would notice that happening.

Looks like I might have to hook the SG back up and do some experimenting. Is fuel cutoff more prevalent in certain makes, models, or since a certain year?

[Bruce]

Originally Posted by pumaman

you're saying the engine automatically restarts so it can idle and provide power while you're in neutral? I would think you would notice that happening.

...Is fuel cutoff more prevalent in certain makes, models, or since a certain year?

You can definitely tell when fuel cutoff ends in my car when it's at fast idle. If you're coasting down in gear to an intersection in gear at fast idle (when the PCM only allows 2d gear max anyway), the car will slow down until it's below the fast idle speed. At that point, it jerks slightly and maintains the idle RPM closed-loop, which also maintains a certain minimum speed.

AFAIK Fuel cutoff doesn't exist in carbureted cars, so it wouldn't have existed at all before the mid-1980s, when fuel injection started becoming more common. My car's engine was in production in 1998, although the previous generation may have had it as well.

[Shrek]

Originally Posted by pumaman

Looks like I might have to hook the SG back up and do some experimenting. Is fuel cutoff more prevalent in certain makes, models, or since a certain year?

Toyota has been using it for many years now. I'll guess since 1986-1990 (?)

[pumaman]

Thanks. My car does act like it has it.