MDS at Idle?

[11B4X4]

As I was sitting at a railroad crossing watching my MPG drop and thumping away on all 8 cylinders I couldn't help but wonder why the truck couldn't drop to 4 cylinders while idling. If I can stay in ECO at 75mph with 35" tires and all electronics going, i'm sure 4 cylinders could get the job done at idle. In theory that would cut fuel consumption in half at idle.

Any Idea's why the Ram wasn't engineered to have this function? Maybe something that can be programmed using a tuner?

 

[Dusty1948]

Except for the valve portion of the MDS system, you could simulate what the idle would be like by removing power to four of the cylinders. I don't think you'd like it.

In the simplest terms, most engines require all that all cylinders fire at extremely low RPMs (idle speeds) in order to keep the engine running. That's because there wouldn't be enough power to over come the friction losses produced by the cylinders that wouldn't be firing. There would be other technical reasons as well.

Best regards,
Dusty

2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, factory dual exhaust, 18” wheels. Now at: 013322 miles.

 

[RedRocketZ28]

You wouldn't even notice the fuel savings at idle.

 

[silverbullet]

1. Can't see it saving much fuel
2. Would sound terrible and not too many want a four popper sound
3. Personally I wouldn't want to lose a bit of the luxury car refinement that this powertrain offers at idle. Silky smooth.

I'm embarassed to admit it but I actually left my truck running a couple of weeks ago, got out, locked the door and walked right on away to pick up my son from school. I remember thinking I heard an engine running and that it must be the dumbass parked beside me just burning fuel in a parking spot; there was a dumbass involved but it was me, haha. I got back to the truck and could not believe I actually did it and had no clue at the time. I should have been tipped off when the 15 year old Eclipse that I 'thought' I heard running was quiet and refined....

 

[11B4X4]

Except for the valve portion of the MDS system, you could simulate what the idle would be like by removing power to four of the cylinders. I don't think you'd like it.

In the simplest terms, most engines require all that all cylinders fire at extremely low RPMs (idle speeds) in order to keep the engine running. That's because there wouldn't be enough power to over come the friction losses produced by the cylinders that wouldn't be firing. There would be other technical reasons as well.

Best regards,
Dusty

2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, factory dual exhaust, 18” wheels. Now at: 013322 miles.

Good information! thanks. Makes sense though.

You wouldn't even notice the fuel savings at idle.

True, but do you really think the motorized air dam or grill flaps really make a huge difference by themselves? probably not. Fuel efficiency is cumulative with all these new technologies and supplementary features.

 

[Reduxalicious]

I think even with the Etorque you have to be stopped for at a minimum of 7-10 seconds before you'll use less fuel for starting than having just idled.

 

[SacRebel]

I was recently wondering this too, makes no sense to run all 8 cylinders when idling.

 

[11B4X4]

I think even with the Etorque you have to be stopped for at a minimum of 7-10 seconds before you'll use less fuel for starting than having just idled.

I don't have Etorque, but i'm pretty sure the auxiliary battery is used for starting the truck, so no fuel should used for that process.

 

[silver billet]

I think even with the Etorque you have to be stopped for at a minimum of 7-10 seconds before you'll use less fuel for starting than having just idled.

Really? You think a truck uses 7 to 10 seconds worth of fuel while idling, simply to start a truck in < half a second?

 

[SacRebel]

I read somewhere the Hemi uses about 1.5 ounces of fuel while idling for 90-seconds. So yes, it adds up.

 

[JJRamTX]

My e-torque is I believe, set at 2 seconds for all shutdowns while the Transmission is in drive. I am seeing the MPG keep moving up and the average is now about 17.1 MPG. The only thing I have found annoying with this so far is when traffic comes to a stop for 2 seconds using the Adaptive Cruise. When the car in front of me starts moving away the engine restarts but it doesn't start the vehicle moving until you hit the resume or the gas pedal.

 

[Dusty1948]

Really? You think a truck uses 7 to 10 seconds worth of fuel while idling, simply to start a truck in < half a second?

Depends on the engine total displacement and the temperature. Reciprocating gasoline engines in general like a richer fuel mixture to start, - even when ambient temperatures are high - the extent is variable by conditions. If an engine is immediately restarted after shut down, it won't need a rich mixture. That's because surface temperatures of all the contact metal (piston, cylinder walls, cylinder head, valves, intake) will cause fuel droplets to atomize quickly and combustion will start easily. Engine computers nowadays adjust the amount of fuel needed for start-ups by reading air, fuel, and coolant temps, and adjust mixture accordingly.

Best regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, factory dual exhaust, 18” wheels. Now at: 013346 miles.

 

[silver billet]

Depends on the engine total displacement and the temperature. Reciprocating gasoline engines in general like a richer fuel mixture to start, - even when ambient temperatures are high - the extent is variable by conditions. If an engine is immediately restarted after shut down, it won't need a rich mixture. That's because surface temperatures of all the contact metal (piston, cylinder walls, cylinder head, valves, intake) will cause fuel droplets to atomize quickly and combustion will start easily. Engine computers nowadays adjust the amount of fuel needed for start-ups by reading air, fuel, and coolant temps, and adjust mixture accordingly.

Best regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, factory dual exhaust, 18” wheels. Now at: 013346 miles.

That's all fine and dandy; but no way does it use 7 seconds worth of idling fuel to start a truck during "start stop". That just doesn't pass the sniffer test, sorry. Reminds me of the myth that was circling when I was growing up, that it used more electricity to turn on a lightbulb then it took to run it for a minute or whatever yada yada. All nonsense.

 

[Reduxalicious]

That's all fine and dandy; but no way does it use 7 seconds worth of idling fuel to start a truck during "start stop". That just doesn't pass the sniffer test, sorry. Reminds me of the myth that was circling when I was growing up, that it used more electricity to turn on a lightbulb then it took to run it for a minute or whatever yada yada. All nonsense.

SAE Journal,

2004-06-08
Fuel Consumption Improvement of Vehicles by Idling Stop 2004-01-1896


They took two identical 4 cylinder vehicles one with start/stop another without, and found after 6.4-7.0 seconds you waste more fuel idling than shutting off and starting, I imagine a 5.7L V8 is going to consume more idling than a 1.5L I4 so the seconds maybe + or -, I would imagine less time on a Hemi

 

[392DCGC]

I think even with the Etorque you have to be stopped for at a minimum of 7-10 seconds before you'll use less fuel for starting than having just idled.

No, you're thinking of traditional start/stop systems that use fuel and the starter to spin up the engine... eTorque uses the eletric motor with stored electricity, not fuel, to spin up the engine.

Really? You think a truck uses 7 to 10 seconds worth of fuel while idling, simply to start a truck in < half a second?

That's all fine and dandy; but no way does it use 7 seconds worth of idling fuel to start a truck during "start stop". That just doesn't pass the sniffer test, sorry. Reminds me of the myth that was circling when I was growing up, that it used more electricity to turn on a lightbulb then it took to run it for a minute or whatever yada yada. All nonsense.

It takes more fuel to start an engine than it does to idle for the equivalent start time. Your "sniffer test" is wrong, sorry bud. Do some research, as the post above mine has sourced for you.

 

[Dusty1948]

That's all fine and dandy; but no way does it use 7 seconds worth of idling fuel to start a truck during "start stop". That just doesn't pass the sniffer test, sorry. Reminds me of the myth that was circling when I was growing up, that it used more electricity to turn on a lightbulb then it took to run it for a minute or whatever yada yada. All nonsense.

I assume you're not going to like this response, either.

There's this thing called in-rush current. When you first apply electrical power to a load there is a peak electron transfer (inrush) that can be many times the normal current draw (current=electrical speed). Depending on the load device, this could represent a large amount of current. So, it is true that the device will consume a higher amount of electrical energy at initial start than is required to run the device for X period of time. This would be true for a light bulb (especially true for florescence lamps) and any load.

I don't know where the 7 seconds came from, or your 1 minute light bulb, so I'm not defending the numbers. But the principles are solid.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, factory dual exhaust, 18” wheels. Now at: 013355 miles.

 

[Reduxalicious]

No, you're thinking of traditional start/stop systems that use fuel and the starter to spin up the engine... eTorque uses the eletric motor with stored electricity, not fuel, to spin up the engine.

That makes sense!

Thanks, my bad.

 

[silver billet]

I assume you're not going to like this response, either.

There's this thing called in-rush current. When you first apply electrical power to a load there is a peak electron transfer (inrush) that can be many times the normal current draw (current=electrical speed). Depending on the load device, this could represent a large amount of current. So, it is true that the device will consume a higher amount of electrical energy at initial start than is required to run the device for X period of time. This would be true for a light bulb (especially true for florescence lamps) and any load.

I don't know where the 7 seconds came from, or your 1 minute light bulb, so I'm not defending the numbers. But the principles are solid.

Regards,
Dusty
2019 Ram 1500 Billet Silver Laramie Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33 gallon fuel tank, factory dual exhaust, 18” wheels. Now at: 013355 miles.

I don't have any trouble believing the idea, just the details. 7 to 10 seconds sounds way too longer, regardless of what that journal says, but I'm not an engineer so ... ¯\_(ツ)_/¯

 

[stevj]

According to my Scangauge, my 5.7L uses 0.3 gallons per hour while idling, once engine and transmission are at operating temperature.
That's 42.6 fl oz or just about 2.5 pints of gas.

Steve

 

[knightro84]

Chevy thought of this concept already and took it a step further so that you could be in 4-cylinder mode all the time. Yes, thats right, all the time. They achieved this feat not by updating the cylinder deactivation software for the 5.3 or 6.2, but just went ahead and put a 2.7L 4 banger in the Silverado. Never have to worry about running on all 8 cylinders if half of them aren't there!