Fuel Cutoff question

[k8crd]

Can you check with a Scan-gauge II if your vehicle has fuel cutoff?

If yes, what is the procedure?

Paul

[cfg83]

k8crd -

Here is one way that may work :

1 - Go to instant gauge section and set one of the gauges to be MPG.

2 - Drive around in gear.

3 - Take foot off accelerator pedal. If the instant MPG is 9999, then you probably have fuel cutoff.

CarloSW2

[k8crd]

CarloSW2:

Thank you for replying!

I did what you suggested with instaneous mpg gage, rpm gage, and tps gage set on the scan gauge and car in gear.

When the foot is removed and the tps drops to 19 at approximately 1600 rpm the instaneous mpg goes to 150 MPG instead of 9999.

My scan gauge was purchased in 12/06 so maybe only the lastest version of it reads 9999 ????


Paul

[cfg83]

k8crd -

Originally Posted by k8crd

CarloSW2:

Thank you for replying!

I did what you suggested with instaneous mpg gage, rpm gage, and tps gage set on the scan gauge and car in gear.

When the foot is removed and the tps drops to 19 at approximately 1600 rpm the instaneous mpg goes to 150 MPG instead of 9999.

My scan gauge was purchased in 12/06 so maybe only the lastest version of it reads 9999 ????

Paul

That sounds similar to what I see. The "9999" is most likely a compromise MPG. When there is fuel cutoff, there is essentially infinite MPG. This is a divide my zero condition ( "N" MPH / 0 GPH), so the Scangauge compensates by reporting maximum MPG that can be displayed on your screen, aka 9999.

In terms of which version reads 9999, I think this would be the same across firmware versions. I have an SGI, so I don't have the better version that you have. If you go to the ScanGauge website, you can download these manuals to see what version of the firmware you have :

Product Support Center
http://www.scangauge.com/support/

ScanGaugeII With XGauge
ScanGaugeII (probably yours)
ScanGauge I : Ver 2.51 (mine, )

If I had an SGII with the firmware version that supports XGauge, I would try to create an XGauge for the short term fuel trim. This would require you to get the specs on the "request id" (not the right name) for the short term fuel trim for your car. I think this is likely to be unique for different car ECU/PCMs.

Feel free to contact the Scangauge folks with your question :

Contact us by e-mail
http://www.scangauge.com/contactus.shtml

General information & Inquires scangauge@linear-logic.com

CarloSW2

[8307c4]

No, most engines do not cut off fuel to the engine, ever.
That's 99.999% of them, do NOT.
Thank you.

[GasSavers_Rotareneg]

Originally Posted by 8307c4

No, most engines do not cut off fuel to the engine, ever.
That's 99.999% of them, do NOT.
Thank you.

I guess I'm one of the lucky few to drive some of the 0.001% of cars that have deceleration fuel cut-off? My old '87 Cavalier and my current '07 Aveo both do it. Older Scangauges (including IIs with older firmware) don't show fuel cut-off in the MPG and GPH gauges with many vehicles, so look at the LP gauge to see if it goes into open-loop while decelerating. My Aveo won't enter DFCO below 40 mph, regardless of the gear it's in, and it stays in DFCO until around 1200 rpms.

[DracoFelis]

Originally Posted by 8307c4

No, most engines do not cut off fuel to the engine, ever.
That's 99.999% of them, do NOT.
Thank you.

WRONG!

These days MANY (the majority?) of normal gas (I am NOT talking about "hybrid", but rather regular fuel injected gas engines) will in fact cut fuel under some very specific circumstances.

Specifically, if you are in gear, and your engine is warmed up, and your foot is totally off the gas pedal, and your RPMs (from the wheels turning against the pavement) are "fast enough" (with many cars "fast enough" seems to be somewhere in the 900 to 1300 RPM range, depending upon the vehicle), THEN many (most?) engines will in fact cut the fuel completely (i.e. they use zero fuel in that case, unlike "idle" which will still use a minimal amount of fuel). They do this because the engine computer realizes that you don't currently need any power (caused by burning fuel) in such cases, and therefore cuts the (currently not needed for the car) fuel to the fuel injector(s). And as soon as you go out of this very specific situation, the engine computer automatically restores fuel to the car, without you having to take any actions to make this occur!

NOTE: You will get at least some slowdown ("engine braking") when this occurs (although factors such as well lubricating your engine, transmission, and drive train, can help to lower the slowdown when doing so), unless you are sufficiently going down hill to let gravity be your friend. However, there are still times when this is a good idea FE wise, such as "coasting" up to a red light you are approaching (or "coasting" up to the stop sign at the end of an off ramp). In such cases, you might not care that you are gradually slowing down (due to the natural "engine braking"), especially if/when it means you are getting the distance "free" (i.e. without fuel use)!

NOTE: DFCO (Deceleration Fuel Cut-Off, which is what they call this), was apparently originally designed to help the auto makers meet emission standards, not for fuel economy (the fuel economy savings, is just a nice "bonus", that those on this site like to take advantage of). It turns out that when you really don't need extra power in a car, dumping fuel in the engine (i.e. "wasting fuel", as old style carburetors used to do) will greatly increase the emissions (requiring extra emission control devices to compensate). But when you are going with computer controlled fuel injection (what most cars these days use), it's easy/trivial for the engine computer to detect such a situation and simply cut the fuel when it occurs (thereby not only saving fuel, which people on this site like, but also lowering the emissions that would otherwise occur in this situation).

[slurp812]

Originally Posted by 8307c4

No, most engines do not cut off fuel to the engine, ever.
That's 99.999% of them, do NOT.
Thank you.

1994 Honda Accord EX does, and so does my 2002 Honda Civic Si. That is a pretty good bet most, if not all Honda's since at least 1994 do. I also believe that Honda sells more than .001% of the autos in the US, so your math may be a bit off...

[hybriDatsun350]

Originally Posted by 8307c4

No, most engines do not cut off fuel to the engine, ever.
That's 99.999% of them, do NOT.
Thank you.

I'd like to know where you got your numbers? My Integra definitely cuts fuel on deceleration. It keeps the injectors off all the way down to about 1100 rpm.

[JanGeo]

The way I figured it out was going down hill when the engine was cold and I noticed that the engine didn't get warmer = no fuel injected.