Scary Near Miss: Has anyone else experienced this? - Page 2 - Dodge Challenger Forum: Challenger & SRT8 Forums
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#11 (permalink) Old 11-26-2012, 12:18 AM
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Just FYI, coasting in neutral with an efi motor uses more fuel than letting the engine be driven by the drivetrain while going downhill.


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#12 (permalink) Old 11-26-2012, 09:43 AM
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I've done that and it's one of the reasons I hate autostick. I've been driving manual tarnsmissions for almost 30 years and once in awhile i try to "shift" my autostick. I'll be glad when i get this MDS turned off so i can drive my auto in peace.
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#13 (permalink) Old 11-26-2012, 09:52 AM
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Glad you, the wife, and the Challenger are OK.

When I'm on the highway and cruising at 80 sometimes I'll drop it into neutral and just glide for 1/2 - 1 mile or until I hit about 60.

When you put the car back into drive there is a 2-3 second delay from neutral.

When you are in auto-stick and want to get back into auto-drive just hold it to the right for 1 second and it will go back.
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#14 (permalink) Old 11-26-2012, 10:31 AM
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Originally Posted by Bradd_D View Post
I've done that and it's one of the reasons I hate autostick. I've been driving manual tarnsmissions for almost 30 years and once in awhile i try to "shift" my autostick. I'll be glad when i get this MDS turned off so i can drive my auto in peace.
I used to feel the same way. I was not explained what the +/- was all about on a Magnum loaner I had once so I just tried it and messed up a few times. I'd do the go to Neutral thing to get back in Drive. Felt like a gimmick and potential trouble for the tranny. So when I bought my Charger I told the salesman not to bother and that I wouldn't be using the feature. I've been getting into the old-dog-won't-learn-new-trick mode for a few years now.

Fast forward to reading up on it online and trying it out... and I really took to it (and I'm slow). No, it's not 100% control like a real manual, but the tranny just follows its programming instructions to save itself. And shifts are suggestions, not actuations, which rubs the control freak and computer-hater in me the wrong way. BUT, if your choice is an auto AND you miss the more spirited/connected driving that manuals give you (I did), on top of the invaluable ability to use engine braking... I really think that you should give yourself more time to learn it because you're missing out. A lot more rewarding (especially with a performance car) than hanging on to the steering wheel and waiting for the car to do things on its own.

Since moving on to a Challenger which, besides being new and in better shape, has the Sport Mode option (no upshifting at redline, a frequent gripe) and a quicker responding TCM it seems, AutoStick has become even more enjoyable and I couldn't do without it now. My current learning curve is about transitions between stick and paddles, but that's just another hurdle for the ol' dog...
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#15 (permalink) Old 11-27-2012, 09:44 AM
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Just FYI, coasting in neutral with an efi motor uses more fuel than letting the engine be driven by the drivetrain while going downhill.



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Not saying you're wrong or I am right but how does this compute when i take it out of gear and the engine rpm's "drop" from nearly 2000 to 750 for the duration of the downhill roll? Also, the truck (in my case) picks up considerable speed in "coast" going down the hill and subsequent inertia that carries it over minor hills after the first drop before I lose enough speed to put it back in "Drive" again. Ineed some serious convincing that an engine running at 2000rpm for 45 seconds uses less fuel than the same engine running at 750rpm for a full minute.

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#16 (permalink) Old 11-27-2012, 11:02 AM
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Not saying you're wrong or I am right but how does this compute when i take it out of gear and the engine rpm's "drop" from nearly 2000 to 750 for the duration of the downhill roll? Also, the truck (in my case) picks up considerable speed in "coast" going down the hill and subsequent inertia that carries it over minor hills after the first drop before I lose enough speed to put it back in "Drive" again. Ineed some serious convincing that an engine running at 2000rpm for 45 seconds uses less fuel than the same engine running at 750rpm for a full minute.
I didn't understand that logic either.

4k RPMS uses more fuel then 800 RPMS I would assume?
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#17 (permalink) Old 11-27-2012, 12:02 PM
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Originally Posted by Redliner View Post
Not saying you're wrong or I am right but how does this compute when i take it out of gear and the engine rpm's "drop" from nearly 2000 to 750 for the duration of the downhill roll? Also, the truck (in my case) picks up considerable speed in "coast" going down the hill and subsequent inertia that carries it over minor hills after the first drop before I lose enough speed to put it back in "Drive" again. Ineed some serious convincing that an engine running at 2000rpm for 45 seconds uses less fuel than the same engine running at 750rpm for a full minute.
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I didn't understand that logic either.

4k RPMS uses more fuel then 800 RPMS I would assume?
It has nothing to do with RPMs and everything to do with fuel need/demand. An engine that's idling takes gas to stay running while an engine going downhill in gear with zero throttle input, that is actually providing engine braking, has zero fuel demand and as a result the PCM doesn't fire the injectors. So, an engine idling in neutral while going downhill actually uses more fuel than an engine left in gear with zero throttle input while going dowhill (Which uses zero fuel in this case).
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#18 (permalink) Old 11-27-2012, 03:24 PM
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Another reason i love my 6speed. it goes to what ever gear i tell it to and cannot talk back. Glad to hear you are safe. i used to coast in N in my grand am all the time. i could put it back to D whenever and it was fine.

As far as the newer engines, in the new challengers when you are coasting in gear, the road drives the engine and not fuel. best way to recoupe those mpgs




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#19 (permalink) Old 11-28-2012, 08:27 AM
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It has nothing to do with RPMs and everything to do with fuel need/demand. An engine that's idling takes gas to stay running while an engine going downhill in gear with zero throttle input, that is actually providing engine braking, has zero fuel demand and as a result the PCM doesn't fire the injectors. So, an engine idling in neutral while going downhill actually uses more fuel than an engine left in gear with zero throttle input while going dowhill (Which uses zero fuel in this case).
so............does the engine (In my case a 1995 Toyota T-100 without the latest technological advances), "run" with ZERO fuel being ingested when left in gear and coasting down a hill? If that is the case, why doesn't it "die" and after the load is re-applied, you feel some sort of restart? Are you telling me that these cars that I "can" coast at 60mph+ in and then drop back in gear are essentially shutting off and then restarting?
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#20 (permalink) Old 11-28-2012, 10:21 AM
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Originally Posted by Redliner View Post
so............does the engine (In my case a 1995 Toyota T-100 without the latest technological advances), "run" with ZERO fuel being ingested when left in gear and coasting down a hill? If that is the case, why doesn't it "die" and after the load is re-applied, you feel some sort of restart? Are you telling me that these cars that I "can" coast at 60mph+ in and then drop back in gear are essentially shutting off and then restarting?
You sound a bit confused, so I'll just explain it in a way you might understand better.

When coasting downhill in gear with a modern EFI engine the engine is being "driven" by the road, which is turning the tires, which turns the driveshaft, transmission, and engine. The fuel demand is zero, no fuel is delivered, and the engine is putting out no power. The engine is actually "absorbing" power in the form of engine braking, which will slowly slow you down. In this state you are using no fuel because none is required. The engine doesn't die because it's not disconnected from the drivetrain or the road, all of the other systems are still functioning as well, there's just no fuel so the engine is acting like a big air pump.

When freewheeling downhill in neutral, the engine is disconnected from the road so in order to stay running in this state requires fuel, just as if you were sitting parked in your driveway. Take away the fuel here and the engine dies, you lose power steering, eventually you lose power brake assist, etc.

Maybe thinking about a bicycle will help?

Coasting downhill in gear is sort of like coasting downhill on a bike with your feet still in the pedals. Let's assume it's an older bike that can't freewheel, if the bike is moving then the pedals are moving. In this scenario your feet never leave the pedals, your legs are moving but you're not doing any work. Have you disconnected anything from the chain or tires by coasting? Nope. Are you able to transition to pedaling without changing anything else? Yup. Are you what's moving your legs? Nope, the movement of the wheels on the ground is moving them for you.

Now let's do the same scenario, only this time you take your feet off the pedals. If you want to move your legs now, what supplies the power/energy? Your body. Is it easy to transition back to pedaling now that your feet are removed from the pedals which continue to spin at a pretty fast rate? Nope.

Not the best example, but maybe it helps get the point across. Kinetic energy turns the engine and keeps it "running" when your foot is off the gas but it's still in gear. Kinetic energy requires no gasoline.
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