Fuel Injector shut-off while Coasting
 

I saw on a couple of threads that the fuel injectors on some autos shut down while caosting in gear. Does this apply to most newer cars? I've been coasting to stop lights and such in neutral cause my rpms stay at idle, but if the injectors shut-off while coasting in gear this would be pointless.

Anyone know more on this subject?

My understanding is that
 

My understanding is that some fuel injected cars at one time did shut off fuel on decel, BUT when OBDII came to be they discontinued this trick in order to keep fuel burning and the cat converter up to temp.

Re: My understanding is that
 

what no way! maybe that's why the scangauge doesn't report 0 L/100km when your foot is off the accelerator and revs are above at least 1000 (should say in your manual). But some reported that it is a scangauge bug and the answer is still not clear...

all i know is, at least the instanteous gauge says im' getting kick *** mileage than if my foot is on the accelerator, so if you do have to slow down, do it in gear, neutral just forces you to use more brakes.

Re: My understanding is that
 

I think you are right on. I think only those TBI OBDI vehicles did this due to the fuel vapors remaining in the intake manifold(harder to control those loose vapors(and of course they did it for emissions). And maybe even the DPFI, MPFI and SFI vehicles too...but on those it would amount to such a small cutoff that it might be immeasurable. I'll have access to a scanner to find out whether my engine does this upon decel in june.

Re: Fuel Injector shut-off while Coasting
 

your garage shows your car as a "5AT" - is it an automatic?

i know that helga does it.
 

i know that helga does it. just my $.02 :D

Re: My understanding is that
 

it's clear to me: my car's factory service manual says injection shuts off under deceleration. the scangauge never showed this, so i'd call that a bug in the scangauge.

my car is ODBII.

I love my OBDI. The
 

I love my OBDI. The SuperMID shows 0.0 pulse width and pags out at 99.9 km/L (235 MPG) in any gear over 1200 rpm with the throttle closed.

Re: My understanding is that
 

Both my VW and BMW do it. My experience is that if the catalyst is hot and the engine speed is high enough, the ECU decides to shut down unnecesary idle fuel. Atleast in the BMW with an analog mpg gauge, I can see exactly when the shutoff happens. Assuming the cat is hot, if the RPMs are above about 1500 while coasting in gear, it usually takes about 2-3 seconds of normal idle flow but then shuts off. It keeps it off until the RPMs fall below about 1000 (idle is about 650). If I'm on a long hill and I have to keep the speed from increasing (either for traffic or to avoid speeding), I can sometimes do this for a long way. It really pushes up the average mpg.

It's an interesting game to play because it's often better to 'spend' the momentum I've already invested in, and coast farther with the clutch in letting the engine idle. In these cases I also consider how far I am likely to coast. If it's pretty far, sometimes it's better to speed up slightly (as in a pulse) and then glide at a higher speed. Since the idle fuel flow is constant, my higher speed in these cases turns into mpg numbers.

And then there are times when I need to slow down and surrender my precious momentum, such as for traffic, stop signs, lights, sharp corners, etc. Rather than just squander it on merely heating and wearing my brakes, I try to take advantage of the shutoff function. In these cases, vehicle speed is irrelevant and RPM is all important. I have to choose the right gear and then brake only when I finally have to stop. :)

Now if only there was a way I could derive the defining algorithim. Of course then I'd want to add automatic shutdown/bump starts, then automatic FAS and restarts when stopped, regenerative braking, not to mention aero, A/C and P/S mods, and... :P

yes, suddenly driving has
 

yes, suddenly driving has become complex enough that even the radio is a distraction! never mind cell phones, sightseeing, daydreaming...

Re: yes, suddenly driving has
 

yeah, that's all I'm sayin'... ;)

Well said.

Re: Fuel Injector shut-off while Coasting
 

my car is an auto with five gears. A first on the civic. I do notice that it likes to hold the gear while deccelerating. It'll get down to about 800 rpms before down shifting when coasting.

So are you guys saying that it is more likely that OBD1 cars do this and not so much newer ones? I know metro said his was OBDII. Is there a way to find this out without having to call a honda engineer?

Re: Fuel Injector shut-off while Coasting
 

i think it's likely that most, if not all OBDII cars do this once they've reached operating temperature.

but... i believe only cars with *manual* transmissions do it.

if the injectors shut down in an automatic, there's nothing to keep the engine turning (no direct connection to the wheels). the engine will stop when the fuel stops.

Re: Fuel Injector shut-off while Coasting
 

I was actually wondering about that. I do experience engine braking when deccelerating, but probably not to the point where if the fuel cut off the car would keep going. I keep thinking I should have bought a manual, but the 5th gear ratio at 0.525 is the only thing saving the automatic. I can cruise at 50mph turning over at 1600 rpms.

Re: Fuel Injector shut-off while Coasting
 

Unless the lockup solenoid is activated... I wonder if this is the case?

Lock-up solenoid?
 

No clue. The inner workings of an auto tranny are still a mystery to me. I could tell you all about genes, DNA, and complex molecular reactions, but auto trannies .... it's like pandora's box

I doubt there is a service manual I could get my hands on at this point in time since the car is so new. I suppose I could bombard Honda with e-mails, but I have a feeling they'd be reluctant to share the specifics.

So if the injectors don't shut off completely, do you think that the fuel input would be reduced since there is no load (however I'm not sure if engine braking would be considered a load by the ECU) on the engine as opposed to being at idle?

Re: Lock-up solenoid?
 

My intuition would tell me that if any fuel at all is injected, it is very little. My knowledge is solely based off of OBD-1 technology, but I do know that MAP, TP, and RPM all play key roles in the amount of fuel injected, and deceleration is 0% throttle, so that has to count for something.

I've noticed something
 

Via the ScanGauge, I noticed something. I figured that coasting in Drive would be more efficient because of the FI cutoff, but that doesn't seem to be the case. When forced to idle in Neutral and coast, the FE goes up considerably, even at slower speeds. So anymore, I just pop it into N and coast just about anywhere possible, and the results have yielded at least a 1-2 mpg increase, not including more FE with engine-off coasting.

Something to consider...

Quote:Via the ScanGauge, I
 

When I noticed that my cel was coming on as a result of decelerating in D (WTF?) I went back to neutral and so far this tank has netted many more miles halfway through, :p

Re: I've noticed something
 

are you sure your automatic has a cutoff? i'd be surprised.

i noticed teh same thing in my mom's camry automatic when i borrowed it to find its EPA highway speed. while driving through town, the coasting in N beat coasting in D.

Re: I've noticed something
 

i keep telling people, sure you won't have the power of a manual transmission but you can still save gas. Just abuse N and don't use your brakes.... but NOOOOOOOOOOOOOOOOOOOOOOOO people think I'm rubbish....


enjoy paying for the gas sucker. If you haven't noticed, in D there's a potenial truth that somehow the gasoline engine is still feeding power to the torque converter which in turns go to the wheels. With it in N all power to the torque converter is now CUT and enough gas is pumped into the engine to prevent stalling.

By putting it in N you elminate the middle man, doesn't matter if D coasts as well as N, there's still resistance from the torque converter!.

Re: I've noticed something
 

From what I've read, I heard that the fuel injectors give slight pulses of fuel on decel instead of complete cutoff, but I didn't consider it to be a significant amount of fuel. As far as know, it pulses until around 800-900 rpm, then it kicks-into full injection mode to maintain idle, even in gear. Neutral coasting has yielded huge benefits, believe you me.

back to N
 

Looks like I'm going to have to do some more testing on my car. Without the immediate feedback of a scangauge I have to wait through about half a tank to get any kind of estimation. Even then the trfiic around here is so fickle that I could very well see nothing.

coast speed limit
 

Did anyone ever figure out if there was a limit to the speed you can coast an automatic in neutral? There's a hill on the highway that I could coast down but my speed would be around 55-60mph

What do you mean by limit to
 

What do you mean by limit to the speed?

is there a limit to the
 

is there a limit to the point where it wouldn't be good for the tranny to shift from N to D. I remember seeing a thread from Compaq about this but I think they only resolved the "DO not N-bomb" for an auto.

That's only for revving high
 

That's only for revving high in neutral. You're transmission should be seamless anywhere if you're not revving it up. My friend's 02 civic will slip in and out of gear at any speed. Lucky him, mine does the whole grinding, jerking, N to D ****, :(

that's what I thought and
 

that's what I thought and hoped for. I've tried it a couple times and it seemed to work ok. I'm just paranoid cause it's still new. I'm starting to think that buying a new car wasn't such a good idea. My 01 civic coupr was awesome cause it was too old to void the warranty but still new enough that you didn't have to worry about it. Still pissed at that bastard that rear-ended me and drove off.

Re: Fuel Injector shut-off while Coasting
 

If you want to be sure you're car is shutting off the fuel injectors when coasting try this. Put a on/off switch on your fuel pump relay and shut the fuel pump off when coasting or slowing. If you do see an increase in mileage then maybe it's not and if it is, it's not doing it very efficiently. If you don't see a difference then it's working as stated and you need not change anything. Also, check this out. (my invention) https://www.youtube.com/watch?v=kpw_7eTelxg

Re: Fuel Injector shut-off while Coasting
 

This thread has been dead for 5 years.

Anyway, better to hook it up to your fuel injectors. Shutting off your fuel pump will allow your injectors to continue operating until pressure runs out. Not only will that use fuel but it may throw a code for running lean, and it also delays restarting the engine if your fuel pump doesn't build pressure fast enough.

Hooking it up to the fuel injectors is as easy as interrupting the common ground wire used by them all. I don't know if all designs include a ground wire or if some just allow the injectors to ground naturally.

Re: Fuel Injector shut-off while Coasting
 

THC is correct- cutting fuel pump power is not the best method.

When I pull my fuel pump fuse (to depressurize the fuel system so I can safely change my fuel filter) my car will start and run for 2-4 seconds. It will even "try" to start with the next 2-3 attempts of cranking.

Re: Fuel Injector shut-off while Coasting
 

Shutting off your fuel pump is an awful idea. Don't do it.

Re: Fuel Injector shut-off while Coasting
 

There may be a few cars that don't disable the injectors when coasting in gear above 1000-1100 rpm's but that's not the case with most.

Re: Fuel Injector shut-off while Coasting
 

My Accord has a 5-speed automatic and what I've noticed is that while deccelerating the lock-up is still engaged through 5:ft to 3:rd gear down to about 15mph and 900-1000rpm before releasing the lock-up. You can feel the engine locked to and braking the wheels constantly and through every downshift at low rev as you describe at about 900rpm. At the same time I have monitored through an OBD2 interface that the fuel system is in open-loop mode which tells me that the fuel is cut off. I'm very excited to find out if the scangaugee I have ordered will read 999mpg during decceleration. This is when lock-up is engaged to start with. If the engine is cold or you have throttled yourself out of lock-up just before coasting this will probably not work.

Maybe we have similar transmissions.

Re: Fuel Injector shut-off while Coasting
 

It sounds like the current software on the scangauge does report DFCO. Otherwise you have to go by the loop reading with older ones.

Re: Fuel Injector shut-off while Coasting
 

I received the scangauge^e today and installed it. It works just as i hoped it would. The instant L/km shows 0.0 when I let the foot of the throttle from high speed all the way down to 13mph (22km/h). If I coast in N the fuel consuption depends on the speed. The higher the speed the better the fueleconomy is:p .

I haven't done the fill up calibration yet, it will take som more driving for that, but the values I'm getting seem reasonable.

Re: I've noticed something
 

Fixed.

A torque converter is bolted to the flexplate (in a manual car, called the flywheel), bolted to the back side of the crankshaft. You have the rotating mass of the TC spinning which gives momentum unless you turn the ignition off and let the engine stop. You have to imagine a torque converter as a giant fluid filled metal doughnut. Spin the fluid inside, the metal fan-like vanes direct the fluid towards the input shaft and that is what spins the transmission and eventually, the wheels. It's a fluid coupling, not a physical connection. Now then you have lockup torque converters which can physically grab the input shaft and these are very close in efficiency to a regular manual transmission. Feels like letting out the clutch, if driving an automatic normally feels like driving with your foot resting on the clutch pedal.

That is how it's always felt for me since 1994, when I taught myself to drive standard, by myself, in the dead of winter, by buying an '86 Lynx with a 4-speed for $60 at an abandoned car auction. I rode my bike to the auction, wasn't planning to buy a car. I actually bought two, but the '80 Civic 1300DX I got had a thrown timing belt. I did actually drive that Civic. I would leave the clutch out, and crank it in gear long enough to get up to 4-5mph and then I'd jam on the clutch and coast 40-50 feet at a time. That's how I got it out of the impound lot and across the street to a mechanic shop to have it checked out. You can't do that in modern cars. Thought it was something simple, it wasn't. Fix was $700 on a $40 very rusty car, I scrapped it. But I kept the Lynx, sold it later for $350 still with no brakes and no muffler.

I do want a manual shift car for my next car. It's hard to do that though, with the wife demanding a family type vehicle, and I prefer cars with enough metal around me to not die when I get broadsided by Escalades and Land Cruisers. I may have found a solution in Mexico. They made the Chevy Celebrity down there like they did up here in the USA. But the ones in Mexico ALL have a manual transmission. 4-speed through 1986, 5-speed through 1989. Not a single automatic unless it was imported from the USA. Only downside is they're all V6 models, but at least it's only the 2.8L and with that overdrive 5-speed in a lightweight non-AC Celebrity coupe, it should do quite well. Coupes thru 88 only though so I'm torn between the 87-early 88 speed density and the late 88-89 MAF version as they didn't make the coupes in 89 and those late 88 coupes with the MAF system might be hard to find. Then again I like four doors, I have been called a four door ***** before and it won't be the last time.

Re: Fuel Injector shut-off while Coasting
 

I have a 2009 Ford Focus five speed and when I coast, the rpm bounces around between 1000 and 2000. This happens most of the time under all weather conditions. A Ford tech took it for a ride with his computer and his determination was that the catylitic converter was telling the engine that it needed more oxygen to burn off pollutants, so the engine was speeding up and running very lean to pump more oxygen. I'm not satisfied with that answer. If that is true, it still ticks me off that it does that. So, if I never coasted, the pollutants would never get burned off? And what would keep the converter from telling the engine to speed when the car is in gear? Anyone else experience this?

Re: Fuel Injector shut-off while Coasting
 

I agree, that doesn't sound right. It sounds like the tech didn't want to get involved in a very difficult troubleshooting process that won't make much money.

Can you test-drive a similarly equipped 2009 Focus to show him that most don't do that?

Re: Fuel Injector shut-off while Coasting
 

I haven't found a stick to test, yet. I'll probably have to try an automatic.