Isn't it more efficient coasting in gear/engine on?
 

From what I understand, Almost all modern car engines shut off the injectors when the engine is down revving, foot off the gas in gear.

Sure, I won't coast as far a the proponents on here who coast in neutral, engine off...which is very dangerous, and in most jurisdictions, very illegal.

Even coasting in neutral with the engine idling will waste more gas than engine even braking, as is see it.

Thoughts?

1. topic is addressed in other threads.
2. 'all modern engines??????? 1984 and up? 1999 and up?
3. Majority of posters here have 'older' cars.
4. the issue of engine on/ neutral coasting has been determined to be manufacturer specific. Alos addressed in other threads.

for example, the last year of the ford taurus (mayby older ones also) DOES NOT gain any advantages. the rpms DO NOT drop
My 02 (02-06) Infiniti Q45 DOES benefit from engine on/ nuetral coasting DOES make a difference.

My car at 40 MPH, in neutral: ~245 MPG
My car at 40 MPH, engine braking (3rd gear) ~130 MPG

Conclusion: The Toyota Yaris manual transmission DOES NOT DFCO. Approximately twice as many MPG's in neutral.

Cheers.

As mr M says this has been covered - the simple answer is "it depends". Firstly are you looking to maintain as much momentum as possible to coast as long as you can (on the flat) - in which case out of gear wins. Or are you going downhill or slowing to a stop then if your ECU cuts off the injectors in gear wins.

If your car can handle it, and it is legal where you are and you are in full control engine-off wins - the Prius turns the engine off when it can.

You also need to know your car - for example in my Aygo it won't go into fuel shut off mode unless the engine rpm is over ~1400. In a low gear this results in a lot of engine braking, in a high gear less.

So as I tapped it depends - on the scenario, your car and what you feel comfortable with.

Does yours have the same rule as mine - i.e. > 1400 rpm ? These results could be due to the fuel required to maintain idle (~900 rpm) out of gear vs what the ECU thinks is needed at whatever rpm in 3rd at 40 MPH is - I would google this last factor but your US Yaris might be different from our UK one.

Until you have done tests, you haven't seen anything.

With deceleration fuel cut-off (aka engine braking) you have no fuel used but the engine is slowing the car down a lot faster than in engine-on neutral coasting, where you have the engine idling but not slowing the car down.
DFCO will obviously save fuel if you were slowing down anyway.

Even if your engine has DFCO, it is still losing some energy from friction (pistons going up & down, &c) and from pumping losses, so obviously it is not more efficient.

The danger/illegality issues have been addressed elsewhere, so I'll just point out that what you believe - coasting is unsafe, big SUVs are safer than small cars, all your kids are above average - may not match reality :-)

Where are you getting your information for this? If you are using your Ultragauge you have to tell it if you have DFCO it won't tell you.

1 outa 3... :eek: .......My daughter is above average!!!!!!! ;) :D

We call it engine braking, and as it's braking, it's inefficient - unless you need to brake of course.
I've been doing that all my driving life, and it give fairly good mileage.

But if you want to do better than fairly good, you'll also need to drive differently ...
The legal issues that remain here and there, will have to go as all priusses coast ...
They exist from days when brakes were nearly useless and unreliable, so engine braking was almost mandatory to slow down.

You're seeing it wrong ;)
Coasting with the engine on instead of engine braking is what has helped bring down my fuel consumption from already "fairly good" ;)

If youre driving and all of a sudden you need to stop then leave it in gear but if you have a chance to coast to a light from a half mile away then put it in neutral because if you dont you will need to keep your foot on the gas pedal longer to get to that light

I guess the next eco evolution in engines might be a compression release when your engine goes into DFCO...?

Ok, engines newer than 1965!!
I was obviously referring to my car, as I have no idea what model cars other users are driving or what year they were manufactured or whether or not they employ this technique...

My MPG goes to 999.

So does mine but I had to tell the Ultra gauge that I had DFCO.

Aha, see I didn't know that, I figured it would detect it automatically. Currently, my instantaneous MPG drops quite suddenly when shifting from neutral, to in-gear, even if my RPM's are around 3k.

I will research it; I will say that in my pre-Ultragauge days, I noticed a distinct jump from the engine when slowing in-gear and my RPM's dropped below around 1500. I assumed at that time I was experiencing DFCO, and later assumed my car was not doing it because of the Ultragauge's apparent lack of DFCO recognition.

Hm, learn something new every day, eh?

cool. You may be able to "see" what is going on by adding the O2 voltage gauge to your front page for a bit. Once your car is warmed up it will bounce around a bit as the computer corrects the fueling. When you decelerate you will see it go into open loop (little circle thingie on the top right) and the o2 will go lean (0 volts I think).

A side note that I should probably post in instrumentation as well. If you do little to no EOC or P&G where the car's computer is going back and forth from open and closed loop what follows really does not matter. If you are operating in open loop more frequently (such as after restart from EOC or P&G) you may get some odd readings.

I tinkered with Injector Cutoff (what Ultra Gauge calls DFCO) for a while and verified what I was seeing on the ultra gauge with my mpguino just tapped into the injector signal. Ultra Gauge can not "see" what the injectors are doing. It can see open loop and throttle position. So by knowing that your foot is off the throttle and the engine is in open loop it knows you are in Injector Cutoff but only after it has gone into close loop once. If you pulse and glide or EOC on the restart the computer is in open loop mode but Ultra Gauge did not power cycle. UG still thinks the car is being driven "normaly" it sees open loop, with little to no throttle position and "thinks" Injector Cutoff. End result is after an EOC to a stop sign, bump start, get going again shift to 5th and light load cruse to the next coast the UG though I was in Injector Cutoff the whole time (other than the acceleration)

The directions say

I would suggest if you are seeing this effect, set the value as low as possible with the Ultra Gauge still seeing Injector Cutoff when you lift off. By the directions I should set the value to 14 (2l engine x7) Mine is set to around 4 or 5 now. Ultra Gauge is only falsely detecting Injector Cutoff after EOC restart and idle or very low power settings right after restart. Once the car goes back into closed loop mode all is well.

My old-school SG2 just shows the MPG jump. I don't think you have to tell it about DFCO but its been a while since I read the manual.

Pondering asking for an Ultragauge for Christmas - I have been good all year :D

I'd be extremely surprised if it didn't have DFCO - every Toyota I've driven in the last 20 years had it.

Sounds like the idle fuel regulator is kicking in to keep the engine running after using DFCO - though around 1500 seems a bit high for it to kick in.

Euromodder thanks for the responses!

That's exactly what I was implying, I think I just worded it badly. I was replying to my older comment, saying my Ultragauge doesn't display DFCO by default, and that my Seat-of-the-pants gauge made it seem like DFCO was happening, which disagreed with the electronics.
Bestclimb explained how to get the Ultragauge to register it, so all is well!

Anyway, it is neat to learn my car does indeed DFCO. And I could be hazy on the exact RPM's :P

Coasting on neutral with the engine idling is often quoted to increase fuel-efficiency only in vehicles fitted with carburettor. No wonder those start-stop/automatic engine off-coasting systems are getting trendy in the European market.

I guess this fits in this discussion, how can i add some adjustable aero braking for when i coast , so i dont overheat or wear out my brakes, ford escort sedan 1998, maybe sone ideas?

Absolute nonsense - no car is on sale in Europe with a carb - emissions tests here pretty much match the US and are close to Japan.

Start-stop is available on a load of cars here, including some really cheap ones - for FE. Google the Hyundai i10 Blue for the cheapest one.

Start-stop-"cruise" is a new idea punted by VAG. The Prius already does this - Mrs A's turns it's engine off at 90+ if I'm going downhill.

If you're coasting with the engine running, shift into gear and use DFCO. It works with my vehicles. And it gets infinite MPG and causes NO brake wear.

if you are coasting down you are already putting less strain on the braking system than a normal driving. if you need just a little braking DFCO works great if you need less than that a feather touch on the brakes won't heat or wear them much at all.

I monitor open loop/closed loop on my SG2 at all times. When DFCO is active it shows "OPEN LOOP".

You misunderstood me. I was pointing that coasting on neutral is often quoted to be effective only in vehicles fitted with carburettor, and the engine off-coasting emerges as an alternative for EFI vehicles.

Apologies - maybe I misunderstood but still confused - engine off coasting seems a reasonable idea for carb-fed cars. They won't have DFCO so that would be more efficient in all cases, would it not ?

1500 is high? My 1ZZ's injectors turn on at 1500rpm... Idle air control starts letting in extra air at about 1000-1200, I never really watched the load gauge carefully enough to see the load jump, but I know it's there. Fully closed throttle at 1500rpm is in the single digits for load, but idle load is like 18-25%.

English is not my native language. So, what's that DFCO?

And engine off-coasting would really increase efficiency in all cases, but the more accurate management from an EFI increases the savings.

DFCO in my part of the world is Deceleration Fuel Cut Off - basically the FI system determines that the driver has the throttle closed and the engine is being turned over by the car's travel and it shuts off the fuel injection and ignition.

There may be a lower RPM limit - e.g. my engine won't go into it under 1400 RPM (from my experiments - it may be different) but once in that mode I can go slower and the engine won't add fuel until the engine speed us under the idle speed ~ 870 rpm.

Carbs don't - they just spray in whatever based on the air flow - SU carbs are the most efficient for FE as far as I know due to the rising piston design - not perfect by any means though.

EDIT - to answer your question better - assume you are descending a hill and in top gear you can coast even with engine braking. The engine is being turned by the car so the Fi system shuts off fuel and you get infinity MPG and your car's systems (PAS, ABS, EBD etc.) are still powered.

How about shutting off the ignition thus shutting off the fuel supply and opening the throttle full to reduce engine braking, , leave in gear so in emergency you just back off throttle to slow down, admittedly sounds complex but just in theory , ?

I have tried this when I had a kill switch on my Honda, I felt no change in declaration as I opened or closed the throttle. (In a car with a carb you would still be pumping fuel).

5th gear (or what ever the highest gear is) does not provide much braking if you need more down shift or touch the brakes. If you need less coast engine off or engine idling (is still better than any form of braking). If you need some where between top gear engine braking and coasting down just feather the brakes it is not that hard to figure out.

The Fuel cut off that may happen from coasting in gear would occur so infrequently :turtle: in my car that that technique would waste gobs of fuel every time i drove. I live in a mountainous region and yet my car never will coast downhill in 5th gear above 2000 rpm, Most of the time i drive at 1000 rpm meaning the fuel cut off will rarely happen in a unlimited amount of miles of driving, for me in my car.
In gear coasting sucks the distance out of the coast, My estimate is 10-15% less coast distance with the car in gear, meaning the throttle needs to be engaged that much earlier.

I suspect the technique works best in automatic transmission cars, what choice do you have with a auto,in most cases.

I have been unable to detect the RPM at which the fuel cut off occurs on my car.

In my Fabia (1.9 130 PD ASZ engine) the engine would go to "infinity mpg" on the overrun at any RPM over 1000. Under 900 or so it would sometimes jerk because the ECU would switch to the idle setting.

As for the answer to the PO - I still say it depends on the cicumstances - road, car, temp, traffic etc. Don't stick to one technique rigidly. On steep declines use DFCO, on lower declines or the flat use neutral to coast further. If its wildly busy traffic maybe neither is a good idea.

That's good news! There is a good chance my AGR is similar. I like the sounds of that !

The techneque works best when you need to slow down, it's engine braking, that conveniently shuts down fuel while decelerating. If used as braking it helps, unnecessary braking (of any form) is detrimental to good economy.

You might know engine-braking is not so great in Diesels. No wonder trucks are usually fitted with those exhaust-brakes...

Depends on the gearing - 6th in the Fabia is about 34 mph / 1000 rpm so slowing in that gear made very little difference and was enough to go to 199 MPG on the on board and 999.99 on the SG2.