Better MPG coasting in Neutral or in Gear ?

[HTSS_TR]

Originally Posted By: HTSS_TR
According to Ultra Gauge instant MPG (similar to Scan Gauge), my '00 E430 consumes less gas while coasting in neutral than in gear. Existing highway at speed around 60-65 MPH coasting to red light ahead, my Ultra gauge shows 120-130+ MPG in neutral and 70-80+ MPG in gear. Also, I can start coasting in neutral about 1/8-1/4 miles farther than in gear. I thought that with OBD II equipped engines the fuel is cut off while coasting in gear. Remember that this particular exist lane near my house is about a mile long, it was safe for coasting down from 60-70 MPH to about 30-35 MPH at the end of the lane.

Can someone with Ultra gauge or Scan gauge confirm what I experienced ?
Originally Posted By: Vikas
You have to understand that UltraGauge "computes" fuel consumption. It is NOT reported to it. It does that based upon MAF reading and engine speed and engine load. When MAF is not available, it uses MAP reading and assumed volumetric efficiency. It does NOT know the fuel injection pulse width. If the engine is cutting out fuel during the engine braking and/or coasting, UltraGauge will NOT show it.

Coasting in "N" on an automatic is fully retarded, I can not emphasis that enough and I used the term "retarded" intentionally. Don't do that.

- Vikas


I have UltraGauge for few months, I liked to know how to drive more efficient without endanger myself and other drivers on the road. I know that at any given time, driving or cruising or coasting, it is safer to have the transmission in D not in N. Saving few ounces of fuel per trip is not worth the danger to have the transmission in N. I was interest in confirming the fuel cut off when coasting in D, versus some fuel use with transmission in N, and I thought that UltraGauge is the tool to confirm that.

From your post, I agree that UltraGauge could not calculate the instant MPG correctly when you take off the foot from gas pedal to let the car coasting to a stop. That is okay with me, knowing the deficiency of the tool will let me adjust my expectation of the result displayed on the gauge.

 

[d00df00d]

Originally Posted By: demarpaint
Maybe it is the older tech cars I drive, and the newer Jeep I never took note.

Power steering and power brakes are lost when my 88 Ford and 93 Ford are coasting in gear and the engines are off. The 88 is a MT, the 93 an AT. Coasting with the engine on all is fine. I never let the 08 Jeep coast with the engine off, so I have no idea what would happen to brakes, and steering. My guess would be I'd lose the power assist? I thought the term fuel is shut off while coasting might mean, there is just enough fuel to maintain, heat or A/C, and all needed power while coasting. When completely stopped in gear, park, or neutral, an engine is burning fuel to keep running.

Thanks for the patience of those responding to me who are trying to help this older mind learn!

Did you see my post above? All of those accessories don't depend on fuel. They depend on the engine turning.

 

[NHHEMI]

Originally Posted By: HTSS_TR
According to Ultra Gauge instant MPG (similar to Scan Gauge), my '00 E430 consumes less gas while coasting in neutral than in gear. Existing highway at speed around 60-65 MPH coasting to red light ahead, my Ultra gauge shows 120-130+ MPG in neutral and 70-80+ MPG in gear. Also, I can start coasting in neutral about 1/8-1/4 miles farther than in gear. I thought that with OBD II equipped engines the fuel is cut off while coasting in gear. Remember that this particular exist lane near my house is about a mile long, it was safe for coasting down from 60-70 MPH to about 30-35 MPH at the end of the lane.

Can someone with Ultra gauge or Scan gauge confirm what I experienced ?


be cautious doing a lot of coasting in N out on the highway. Not sure how they would prove it but it is a ticketable offense...

From CA DMV

V C Section 21710 Coasting Prohibited
Coasting Prohibited
21710. The driver of a motor vehicle when traveling on down grade upon any highway shall not coast with the gears of such vehicle in neutral.

 

[demarpaint]

Originally Posted By: d00df00d
Originally Posted By: demarpaint
Maybe it is the older tech cars I drive, and the newer Jeep I never took note.

Power steering and power brakes are lost when my 88 Ford and 93 Ford are coasting in gear and the engines are off. The 88 is a MT, the 93 an AT. Coasting with the engine on all is fine. I never let the 08 Jeep coast with the engine off, so I have no idea what would happen to brakes, and steering. My guess would be I'd lose the power assist? I thought the term fuel is shut off while coasting might mean, there is just enough fuel to maintain, heat or A/C, and all needed power while coasting. When completely stopped in gear, park, or neutral, an engine is burning fuel to keep running.

Thanks for the patience of those responding to me who are trying to help this older mind learn!

Did you see my post above? All of those accessories don't depend on fuel. They depend on the engine turning.


I did. In fact last night I shut my Aerostar off while coasting in drive, to satisfy my curiosity. The steering becomes more difficult, the brakes got rock hard after pumping them, and the lights dimmed a little.

Maybe cars newer than 1993 are different. BTW I'm not doubting you, but up until 2008 a 1995 Caprice was the newest car I owned. It did the same thing as the Aerostar if shut off in Drive and coasting.

Same thing happens coasting in N with the engine shut off. That's something I won't do with an AT even if it saves gas, risk/reward IMO is just not worth it.

 

[d00df00d]

Originally Posted By: demarpaint
I did. In fact last night I shut my Aerostar off while coasting in drive, to satisfy my curiosity. The steering becomes more difficult, the brakes got rock hard after pumping them, and the lights dimmed a little.

A few points here -- and I'm going to incorporate your '88 Ford here, which I missed earlier (sorry).

When you "coast" in an AT car, the torque converter is unlocked, which means the transmission is mostly disengaged from the engine. The engine will drop to idle speed (maybe a fast idle) and the ECU will use fuel to keep it alive. If you shut it off at that point, the RPMs might drop to zero even if the car is moving; if that happens, you will lose power assists.

As to your '88 Ford, when you tried coasting in gear with the engine off, was the clutch engaged or disengaged? If it was disengaged, then shutting the engine off would cause you to lose power assist just like in the AT scenario above. If it was engaged and you still lost power assist, then I would suspect that the brake and steering assist systems are governed by electronic components that shut off when the ignition is turned off.

 

[CharBaby]

My BIL always told me that by throwing the shifter into "N" while treveling at speeds(whatever speeds), what happens is: the transmissions' torque converter is now NOT turning as fast as the rest of the drive shaft/axel/wheels and, this is NOT GOOD!

I don't know if I explained this correctly but, you get my point!

 

[demarpaint]

Originally Posted By: d00df00d
Originally Posted By: demarpaint
I did. In fact last night I shut my Aerostar off while coasting in drive, to satisfy my curiosity. The steering becomes more difficult, the brakes got rock hard after pumping them, and the lights dimmed a little.

A few points here -- and I'm going to incorporate your '88 Ford here, which I missed earlier (sorry).

When you "coast" in an AT car, the torque converter is unlocked, which means the transmission is mostly disengaged from the engine. The engine will drop to idle speed (maybe a fast idle) and the ECU will use fuel to keep it alive. If you shut it off at that point, the RPMs might drop to zero even if the car is moving; if that happens, you will lose power assists.


As to your '88 Ford, when you tried coasting in gear with the engine off, was the clutch engaged or disengaged? If it was disengaged, then shutting the engine off would cause you to lose power assist just like in the AT scenario above. If it was engaged and you still lost power assist, then I would suspect that the brake and steering assist systems are governed by electronic components that shut off when the ignition is turned off.


I've never intentionally shut the 88 off while coasting, it has stalled in gear coasting, and in neutral. During a problem solving mission. Both times all power assist was lost. Honestly I have no intention of trying it in the 08 Jeep LOL. Thanks for your time explaining.

 

[Vikas]

I will tell you what will happen when you try to go between D to N. Once you will end up in reverse. DON'T ASK ME HOW I KNOW :-(

The way UltraGauge (or similar devices hooked up to OBD-II) compute the fuel consumption is interesting. What happens is that the device know that car ECM is trying to keep the engine at stoichometric (14.7:1) ratio. The UltraGauge *assumes* that the car is running at that ratio and computes the instantaneous gas consumption based upon the amount of air it is ingesting. On my UG, I keep MAF and instantaneous fuel consumption in gallon per hour on the gauge along with % throttle and MPG. You can notice the relationship of the MAF and GPH. They are pretty much linear.

Only the inbuilt MPG calculators would know the fuel injection pulse width and can compute true fuel consumption.

This is my understanding and experience with the circa 2000 model OBD-II cars. It is possible that newer models support lot more parameters and one of them could be true fuel consumption as reported by car ECM but I do not think so.

Sometimes I do coast in neutral if I see the red light ahead but only because I am driving a stick. Coasting in N on an automatic should be extremely rare and should be reserved when you are trying to debug e.g. trying find if the noise is related with the engine speed, car speed or transmission speed and even then do it extremely carefully.

- Vikas

 

[brianl703]

Originally Posted By: d00df00d

When you "coast" in an AT car, the torque converter is unlocked, which means the transmission is mostly disengaged from the engine. The engine will drop to idle speed (maybe a fast idle) and the ECU will use fuel to keep it alive.


This depends on the car and the transmission. The 4R70W (Ford) and the 4T40E (GM) do not exhibit this behavior.

 

[Hokiefyd]

Originally Posted By: d00df00d
When you "coast" in an AT car, the torque converter is unlocked, which means the transmission is mostly disengaged from the engine. The engine will drop to idle speed (maybe a fast idle) and the ECU will use fuel to keep it alive.


This really is dependent on design. Most GMs will keep the torque converter locked during coast. Every Chrysler I've owned does in fact unlock the converter during coast, which annoys the heck out of me.

My '11 Camry would keep the converter locked (and aggressively cut fuel in the engine). So much so, that it felt like driving a manual but without the clutch. Both of our current Honda products (08 CR-V and 05 MDX) also keep the converter engaged during coasting, but the fuel cut isn't as dramatic, and both will slip the converter for a second when you get back on the gas to make the transition smooth.

 

[IndyIan]

On my drive to work, in my car(neon), I get better mileage coasting in N down several hills. I don't know if it hurts the transmission but it can't be too bad as I've been doing it for about 30,000 miles about 15-20 times a day.
The trans is about as complicated as a hammer compared to some cars and doesn't seem to mind so I figure why not, and I can go from D to N to D again with zero chance of find R.
I can't really see any safety issue with being in N rolling a 55mph on a straight highway. I've got full brake boost available and hitting the gas to counter act oversteer is almost useless in an automatic car that has to downshift once or 3 times(with a new 6+ speed auto) to apply any really torque to the front wheels anyways.

 

[mechtech2]

The fuel cutoff from deaccelerating in gear varies from car to car.
But the engine braking is horrible for fuel economy because you are BRAKING.

 

[Mr_Incredible]

I get better mpgs in my 89 CRX DX by coasting in gear. The fuel shutoff feature seems to be fairly agressive. Coasting in neutral is not nearly as efficient. It's a stick.

The 98 Camaro gets the same mpgs on the scangauge coasting in gear or in neutral. But it's an automatic.

Daughter's 96 F150 (I-6) gets WAY better mpg by coasting in neutral than coasting down in gear. It is also a stick.

The 99 F250 SD V10 sucks gas turned off sitting in the driveway.