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Old 02-05-2007, 03:58 AM   #1
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idle in gear

odd but cool

i just found i can drive my car at 30km/h (18mph) in 4th gear without even having my foot on the trottle (look no feet... )the engine seems to run pretty smooth just like when it's idling , yet applying throttle will make produce rattling noises so when speeding up from this speed a downshift is generally required.

can some other cars do this or is this a bad sign?

perhaps idle should be a little lower? due to the cold weather my fast idle speed is set quite high because after a night in the freeze little kadettski is a little grumpy but once it's warmed up everything purrs like a cat slow idle feels normal. i generally turn the engine of at stoplights so perhaps this is not a big issue?
any thoughts on this?
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Old 02-05-2007, 06:00 AM   #2
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I can do this with my mom's car if the a/c is on, it creates enough drag to pull the car along with it, Dunno if it's any good or not though.
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Old 02-05-2007, 09:07 AM   #3
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My car is the same way when cold- my fast idle is about 2000 rpm and this is enough to get me 30 mph in 3rd gear without touching the gas pedal.

It just goes to show how much energy can be wasted when idling- especially when fast idling.
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Old 02-05-2007, 09:16 AM   #4
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lunarhighway -

My parking lot at work is big and flat. When I start the engine, I can slowly engage 1st, 2nd, and 3rd without touching the accelerator pedal before I reach the exit gate and have to join normal traffic. It's cool because each gear ever-so-slowly increases the speed of the car. This way I use the gas *and* am gentle on the engine.

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Old 02-05-2007, 09:35 AM   #5
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You can do this. The problem is that at low rpm's, when you apply a little throttle you get the rattling noises, which is known as lugging. You don't want to lug the engine, it put's tremendous stress on all of the elements of the engine and driveline. It's caused, I believe, by the effort to extract to much power from each piston stroke and the fact that each piston stroke is having more power applied than it can smoothly transfer to the crankshaft and driveline.

It is pretty hard on the engine when it get's lugged. However, with a very light touch on the throttle and some buttock sensitivity, it is possible to use a very light amount of throttle and run the engine at some unusually low speeds and still move the car down the road. Essentially you are up on the edge of extracting as much efficient power transfer as the engine can manage, with as low as possible engine friction losses, because the engine is going so slow.

What I've found is that as I have been making aerodynamic improvements to my car, the speed I can drive at in higher gears keeps coming down. I presume this is because the car is able to move down the road with less power, than previously and consequently if I am light on the gas pedal, I can utilize that to assist me in getting a higher level of mileage than I might, otherwise be able to get.

Neat stuff!
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Old 02-05-2007, 12:58 PM   #6
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I do that in my xB in 5th all the time at about 20 mph it gets about 70mpg on level road. I can also give it just a pinch of gas keeping the SGII reading 40-50mpg and not have the engine lugging rattle but that maybe from the VVT-i engine which runs really smoothly - you want to avoid big power pulses at that low an rpm because the torque springs in the clutch plate are probably bottoming out and is not good for the clutch plate or the gears in the tranny. When really cold like now the 5th gear is accelerating sometimes at 25mph and even at 30mph downhill it kicks in a little more gas to keep the engine emmissions clean.
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Old 02-06-2007, 04:49 PM   #7
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Quote:
Originally Posted by Gary Palmer View Post
You can do this. The problem is that at low rpm's, when you apply a little throttle you get the rattling noises, which is known as lugging.
"Lugging"? Yep, I'm nuts about it. My associates say I'm nuts to do it.

Throttle-by-wire vehicles have the accelerator pedal connected to the engine computer, which has final say on the fuel delivery requested by the driver. Your foot position may not always be the controlling factor. The engine management system may be providing more fuel (and air too for spark ignited gasoline engines) if it senses the rpm is dropping below a 'normal' minimum idle rpm setting.
My TDI has enough torque at 900 rpm idle that I can run through all five gears and 'idle' at 25 mph (40 kph) in 5th gear. Most hills can be crept up in 5th at this rpm since the ECU increases fuel in an attempt to maintain the 900 rpm. Pressing the clutch pedal and freeing the engine from this load allows the rpm to briefly rise until the ECU catches up and reduces fueling.
On the other end of the spectrum is the 'traction control' that takes over when the drive wheels are spinning faster than the non-driven wheels. Most traction controls use the ABS to slow the more freely spinning wheel to match the other drive wheel's rotation rate. Once drive wheels are closely matched the ABS sensors compare the pair's speed to the non-driven wheels. The ECU will frequently be used to reduce the fuel (and air) to limit the torque to a level that the tire's grip can handle.
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Old 02-06-2007, 05:33 PM   #8
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I've heard lugging can be a PITA because of oil pressure, it's usually pretty bad from after idle to the low 1k rpm range. So, for cars that have marginal oiling to begin with, lugging can destroy an engine. That being said, most newer vehicles have good oil pressure, and the minimum is more than enough to lube everything. I've lugged all the M/T vehicles I've owned with nary a problem... If a engine can't take a reasonable amount of max torque/low rpm operation, I'd rather not bother spending time on it's upkeep.
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I think if i could get that type of FE i would have no problem driving a dildo shaped car.
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Old 02-06-2007, 06:02 PM   #9
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Quote:
Originally Posted by omgwtfbyobbq View Post
I've heard lugging can be a PITA because of oil pressure, it's usually pretty bad from after idle to the low 1k rpm range. So, for cars that have marginal oiling to begin with, lugging can destroy an engine. That being said, most newer vehicles have good oil pressure, and the minimum is more than enough to lube everything. I've lugged all the M/T vehicles I've owned with nary a problem... If a engine can't take a reasonable amount of max torque/low rpm operation, I'd rather not bother spending time on it's upkeep.
Maybe the Lug Line is like the Mendoza Line for cars. Would it be safe to say that lugging is putting load on the car below the car's designed idle RPM?

I like to get as close to lug as possible without lugging. As Gary said, stay super light on the throttle.

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Old 02-06-2007, 06:42 PM   #10
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Could be. I've always had the notion that lugging was anywhere between idle and maybe ~1.5k rpm, and in that case, I've never lugged any of my vehicles, but then again, I've never gone down the street slow enough to lug any of 'em. Now that you mention super light throttle, I'll have my pickup buck like a mule under light load in fourth, but when I give it lots of gas going up an incline at ~25mph, it's surprisingly smooth, so that must have to do with my carb, and not lugging per say.
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