Fuel Cutoff question
 

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

If yes, what is the procedure?

Paul

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

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.

Shadetree method... ziptie a plastic tube near your injectors.... feed the other end (gotta be 6ft long or so) through the firewall with the speedo or throttle cable, bring it inside the car.... and listen to the end of it while you're driving.

downhill=no load with high airflow thus no warming up. unless it's a 5 miles downhill, no dice. plus, engine temp change over the length of an average hill is negligeable anyway.

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

k8crd -

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
https://www.scangauge.com/support/
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
https://www.scangauge.com/contactus.shtml
CarloSW2

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.

Ford implemented it in some EEC-III and all EEC-IV and up, so most Fords from about 1990 up should do it. I've heard it's down to 1800RPM but don't know if that's universal or application specific, I believe the EEC-IV reference I got that from was on a Mustang tuner site. Some Mazda's, Jaguars and anything else with Ford engine management should do it. Chrysler's SMEC and SBEC in V6 engine applications is believed to do it from about '87 but don't know RPM or other conditions, may have been more aggressive from '92 up when they changed some stuff. Not sure about chrysler 4 cyl and turbo applications. Don't know about DSM and mitsubishi sourced chryslers. (avenger, stealth, colt etc)

Anyway, since that covers a lot of cars topping the best seller lists since the early 90's, dodge minivans, ford escorts, tauruses, F-150s.... I'd figure that's rather more than 0.001%

In the 1990-1999 Eclipse/Talon/Laser the fuel cutoff threshold is at 1188rpm, with 3/4 seconds delay from when the throttle is closed to when the ecu cuts off fuel. This is done to smooth the transition and to 'enhance a pleasureable driving experience.' The fuel cutoff rpm is raised when engine coolant temps are low, which is also when idle speed is higher.

anyone know when does a 97 civic coupe dx cuts the fuel?

Best way to tell is to shift into 3rd gear at 30 MPH and let your foot off the gas. Wait until you feel the engine start to produce power. The transition is very noticeable for me.

860 RPM with no accessories on, I mean nothing that would kick up idle speed. If I turn the AC on it goes uo to close to 1300 RPM.

Manual transmissions are easy.

Automatics are a lot harder to determine unless you have a scan guage.

When you close the throttle and the manifold vacuum goes very high, there is always some significant reduction in fuel delivery, or you would have high unburned hydrocarbons in the exhaust.

Exceptions would be automatics that dont have a lot of engine braking force when you let completely off the gas. If your foot is touching the gas pedal there is no DFCO.



regards
gary

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).

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...

Is this true? If a car is in DFCO mode, it is in open-loop? I have software that can monitor this status, but haven't had much time to play with it. I'm still not sure if my 98 Corolla has DFCO.

My VW goes open loop during DFCO.

How could it not go into open loop. There is no exhaust to measure the oxygen content relative to the atmosphere, since the atmosphere is both inside and outside, it can only be in open loop.

Sensor reading is 0.

regards
gary

My 96 Civic DX does, so the 97 probably does, too. In gear, above 1200 rpm.

Look for Open Loop on the scangauge. That's a dead giveaway.

Confirmed my 98 Corolla does go into open loop if I shift down into 2 and let off the gas. It won't seem to do it if I'm coasting down in D though. This begs the question whether fuel cutoff is worth doing for engine braking to a stop at a light, where you can achieve DFCO for maybe 5 seconds. That must be a minuscule amount of fuel saved compared to just coasting in D or neutral. Must be weighed against transmission wear and a slight increased risk of hitting reverse!

On a long downhill where you have to stop at the bottom, I'll definitely try to get into DFCO now. Thanks.

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.

It does help enough to be worthwhile. How does it increase your risk of hitting reverse? Don't you have PRND21?

Make sure you confirm the behavior at all speeds where you might use it.

Don't use it in place of neutral coasting when you don't intend to stop or slow down...the total amount of energy saved is more in N in that case.

As I come to a stop, I'll want to be in neutral to either idle or shut off the engine. But going from 2 to N - if I just push the shifter without using the button, it makes a loud clicking noise which I don't like. So I will more often push the button in to shift, which will disengage the lock-out to reverse. Hasn't happened yet, but from what people say here, it's bound to happen once you start shifting automatics more.

My 1994 Grand Am with Quad 4 does DFCO when the mph starts above 55, the TCC is locked, and the gas pedal is off. DFCO never occurs when the TCC is disabled which is any speed 44 mph or less.

DFCO is not hard to detect in an automatic without any instruments. It just happens less often. With DFCO the car will have two different deceleration rates. It will start with idle deceleration then when the ECM determines that all the right conditions are met is the fuel is cut off which will be a stronger deceleration and the engine noise may change.

I use the DFCO ICE-on with my 2002 Honda Civic (auto) all the time. Without it, I'd get around 40-42mpg at about 55 mph trying to minimize the LOD engine load factor (so slowing down going uphill, speeding up going downhill, more or less dead-pedal).

With DFCO ICE-on, I "porpoise" 10 seconds on (75-85% engine load factor per Scan Gauge II), and try and maximize the glide (although it is usually about 5-7 seconds, in moderate to heavy traffic). In spite of the lob-sided 10-on, only 7-glide numbers, I get around 48 mpg that way on the highway, cycling between a low of 55 mph to 60 mph. There's nothing magic about 10 on and 6 off --- just seems easier to do and keep up with traffic.

The porpoising also encourages tailgaters to get around you, cause their cruise control doesn't match with your "porpoising" (p & g).

While there IS a bit more drag with DFCO ICE-on than coasting in N with ICE-off, the difference is not THAT noticible. Most passengers don't even realize that I am porpoising --- the accelleration and decelleration are blended that smoothly, most of the blending work done by the auto tranny, not me.

DFCO ICE-on is wasted in town, below about 35 mph in my case. At low speeds you get about 15-20% further glide with ICE-off in neutral, as the 9999 readings disappear at lower speeds (sub 30 mph in my case, regardless of the tach reading --- that probably is different with different cars, though).

I recently changed the tires from 185/65 R15's to 205/65 R15's (so increasing the rolling diameter by 4.5%) and this adds another 2 mpg over the numbers I've reported above. Whoopie --- over 50 mpg with an auto Civic!

Hope this helps

What kind of car are you driving? I would be relatively certain if it's a Ford that has been make in the last 20 years the answer is yes, because my '88 Escorts both have DFCO. On my '97 Escort when I first installed the Scan Gauge I would get readings of 9999 sometimes, but then for some reason it started reporting high mileage figures varying with speed when I'm not on the accelerator. I've heard of this happening to others too. So I know it does have DFCO.

With an automatic, that technique (which I call "Pulse & DFCO") could work, assuming that the torque converter is unlocked during the DFCO phase. I believe that it would still be more efficient to coast in neutral with the engine on (which I call "Pulse & Glide"). I'm glad to hear that is does work for you. :thumbup:

You should not coast in neutral with the engine off (which I call "Engine Off Coasting", "EOC", or "Pulse & EOC") with an automatic transmission. Most automatic transmissions are designed in such a way that doing so could cause damage.

"You should not coast in neutral with the engine off (which I call "Engine Off Coasting", "EOC", or "Pulse & EOC") with an automatic transmission. Most automatic transmissions are designed in such a way that doing so could cause damage."

Thanks for your caution, however the 2002 Honda Civic autos are fine for coasting with the engine off, and the tranny in neutral. (I can't speak for other years or other models). I've done it for years, and haven't had any problems with my Civics. The most common way of verifying this is to make sure the brand and model of car can itself be towed. In this case see:

https://www.irv2.com/forums/f85/03-ho...wing-7962.html

The more serious concern is that EOC with most cars kills the power steering (the civic is pretty light, but you have to horse it around curves), and the brake pedal has enough umph for about 2 minutes of constant light braking, and then you better turn the engine on, quick! Again, I've had a lot of experience with both phenomena.

Using an automatic, I'm not happy with cycling between EOC pulse, and then going to neutral, and back --- that works great on a 5 speed MT, but that's much tougher on the torque converter in the AT tranny, which has to match higher rotational speeds. So for an automatic the porpoising seems to be a reasonable compromise that gives 50 mpg results at 50-60 mph.

You are correct, checking to see if it can be flat-towed is how you find out if it can EOC. That's good to know about the Civic's transmission. How were you restarting from your EOC? I've heard of bump-starting automatics but I imagine that's a quick way to break stuff.

If you're electric starting or if you're leaving the engine on, there's no reason that the torque converter or the transmissions's clutches need to match any rotational speed at all; you can simply rev-match it with the gas pedal before shifting into D. That's what I do in my automatic, just like in a manual.

Also, as far as higher rotational speeds - the Civic's automatic is geared lower than its manual? Most cars have a taller high gear in their automatic than their manual.

"How were you restarting from your EOC? "

I use extended EOC around town, often on Rat Runs (side roads that are lightly travelled), where I go for LONG coasts in neutral, ICE-off, and short bursts at 80% LOD (engine load factor). Typically 10 second bursts and 30 second plus EOC (where I can get away with it --- the wife's patience usually being the limiting factor).

For low speeds, I just key the motor off to the Run-I detent (and don't bother going back to the Run-II detent --- so, no gauges active, and limited Scan Gauge even on hybrid setting, but I don't have the headlights draining the battery either --- remember we have automatic headlight on in the Great White North). Restart under 15 mph is no problem.

For interest, I do have a 15 watt solar panel in the back window, plugged into the cigarette lighter. Seems to work well at keeping the battery topped off.

I can feel when mine goes into DFCO but that could just be do to the high stall torque converter, not conducive to fuel mileage by the way. I also feel like it changes sound a little bit.

My scangauge will read all 9's in DFCO on the mpg gauge.

So, were you turning the key to "Start" to restart the engine?

"So, were you turning the key to "Start" to restart the engine?"

Yes, I restart using the normal key-on with the Honda Civic (auto) in neutral. Doesn't seem to be any extra wear and tear so far (1 year). It just takes a short 1 second burst when the engine is warmed up, although I hold it for a tad longer, to the point where I hear the starter pick up speed. I don't know of any way of bump-starting this model (although I used to do that a lot with the 71 240z).

For the hard-core Civic user, occasionally my 2002 Civic auto doesn't want to start in neutral; have to stop, put it in park, reverse the key in the lock, and try again. It's always done that, about 1 time in 50 starts, since day 1. Once it decides to be obstinate, you can try starting (with the key in the same orientation) 20-30 times and it just won't go. Mule stubborn. Something to do with the 2002 model and recognizing the "chip" in the key according to my Honda mechanic. (Beats me, but when it won't start worth squat one way, then it starts first time when the key is reversed --- no rhyme nor reason as to which side should be up, or which of 3 keys, either. One time its side A, next time its side B, which I had to mark). Stopping "in gear" can give you some fun trying to start it in neutral, too --- you need to always shift into neutral before you stop. May be just peculiarities of MY car --- who knows, but there is some mention of the automatic gear selection process in that towing link above. I just mention it for other Honda Civic automatic users that try EOC or ICE-off at the lights with puzzling results. None of this is worrisome --- just ... well ... peculiar.

Ok, I see.

With electric starting, you shouldn't have to worry about your torque converter or the transmission in the N->D shift, as long as you rev-match.