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TDI Fuel Economy Discussions about increasing the fuel economy of your TDI engine. Non TDI related postings will be moved or removed.

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Old September 11th, 2006, 11:35   #1
Fix_Until_Broke
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Default What is Engine Lugging?

I've searched my reference material, but have found very little/no information about lugging.

Does anyone have a defined set of conditions where lugging occurs?
I assume it has something to do with the ratio of power stroke cylinder pressure to compression stroke cylinder pressure at any given point in the stroke, and as that ratio approaches 1:1 lugging occurs, the farther away from 1:1 it is, the smoother it will run.

This is just my guessing here - Does anyone know?
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Old September 11th, 2006, 12:28   #2
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i'm sure someone has a set of theoretical numbers for when lugging will occur, my advice is only from personal experience.

[quote=Fix_Until_Broke]MrErlo

So if I'm in 1st or 2nd idling along a flat road (in traffic for example), that's lugging?

I don't suspect that it is quite this clear cut.[/qutoe]

if the car is traveling slower than the engine, then you're lugging. if you're rolling to a stop sign in 2nd at 25 mph, you're clearly not lugging, but if you were trying to do that at 5mph, you'd be able to feel the engine trying to pull you forward and not being able to do so b/c it does not have enough fuel. like i said in all gears this happens for me as i drop below 1200RPM, slightly lower if i'm decelerating by using the breaks heavily.
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Old September 11th, 2006, 12:41   #3
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A good way to look at lugging is to remember riding your bike. When you first took off in a high gear. Going up hill and in high gear you feel the load on your legs. To running smoothly and not pedaling to fast but not working so hard that they ached.
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Old September 11th, 2006, 12:47   #4
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From my experiences, lugging happens most (based on feel and engine sound) at less than 1500 RPM in 4th or 5th and trying to accelerate. 1st through 3rd don't exhibit the same feel/sound.

Trying to accelerate at less than 1500 RPM in 4th or 5th I might out well use my feet to try and help it along.
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Old September 11th, 2006, 14:28   #5
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WJ and Bob are right. i guess i might have been describing a different engine condition, perhaps it's just a different type of lugging. when i roll down a hill in 5th then try to accelerate up the next hill at 35mph in 5th i have the same problem they're describing. gotta down shift, and heck... it's more fun that way.
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Old September 11th, 2006, 15:07   #6
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I know it's got to be the torque, but in all the gassers I used to drive I lugged them a lot, or at least I knew when I was doing it. Take our nice 1988 Mazda 323 hatchback. If I was in 5th and going up a 3% or better grade at 35mpg my speed would drop off and the car would slow and the engine would "chug". That is what I have always considered lugging.

The thing is I can do the same thing with the TDI and it doesn't seem to bog down and can even increase speed if I want to on that same hill in 5th.

My only guess would be when the engine can't produce enough power to accelerate in a given gear. My drive to and from work is all at 35 mph and I am in 5th once I hit 35 and cruise at 40 the whole way, even up that small hill, some might think I am lugging it, but the car doesn't seem to mind.

I am seriously considering the 5th gear swap for highway driving, but since have this drive I am a bit concerned the lower 5th might be to close to lugging on that hill or maybe even 40 mph with the lower gear?
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Old September 11th, 2006, 15:13   #7
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Quote:
Originally Posted by MrErlo
WJ and Bob are right. i guess i might have been describing a different engine condition, perhaps it's just a different type of lugging. when i roll down a hill in 5th then try to accelerate up the next hill at 35mph in 5th i have the same problem they're describing. gotta down shift, and heck... it's more fun that way.
What we described sounds what you're describing too.

What are your RPMS at 35 MPH in 5th?
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Old September 11th, 2006, 15:17   #8
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Quote:
Originally Posted by Bob_Fout
From my experiences, lugging happens most (based on feel and engine sound) at less than 1500 RPM in 4th or 5th and trying to accelerate. 1st through 3rd don't exhibit the same feel/sound.

Trying to accelerate at less than 1500 RPM in 4th or 5th I might out well use my feet to try and help it along.
i wanna know how you can possibly be lugging the engine at 1500 rpm lol

Usually you feel it at around 1250 ish rpm (on flat ground and crusing of course).
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Old September 11th, 2006, 16:30   #9
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Quote:
Originally Posted by TurboBenz
i wanna know how you can possibly be lugging the engine at 1500 rpm lol

Usually you feel it at around 1250 ish rpm (on flat ground and crusing of course).
1500 RPM, 5th gear. Try and accelerate at a reasonble speed. Feel and listen to the motor.
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Old September 11th, 2006, 17:01   #10
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Bob is telling you correct - if you get caught with your RPM's low you must accelerate very gradual. If it groans at all you needed to shift gears. Some areas I can roll along at 1500 in town with no grade. The minute you start to encounter that grade either you anticipated and starting getting those RPM's up or you better shift. You can feel it the seat of your pants when that crankshaft is lugging. If you are real sensative you feel the vibration, thats the clutch load on the crank.
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Old September 11th, 2006, 17:48   #11
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Lugging an Engine......

http://www.cartalk.com/content/colum...August/07.html

Kinda geared toward a gasser but the basic theory still holds...Symptoms
may differ for a diesel. (above link)



Lugging an engine is laboring an engine in too high a gear.
If an engine cannot accelerate smoothly when requested then it
is being lugged.
The solution is to downshift, then accelerate.

HTH.

Bill
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Old September 11th, 2006, 20:04   #12
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All good responses/descriptions of what is felt/conditions during lugging. Having the 0.681 5th and a lot of 40-45 mph driving during my commute, I'm familiar with the feeling.

Why does the engine do this? What causes the excess vibration, shuttering, noise, etc? What is happening in the cylinder(s)? Why is what happens more pronounced at lower engine speeds? Why when pulling a trailer up a hill at ~2000 RPM in 5th at 100% throttle and loosing RPM does this not happen (or I don't feel it) and with no trailer at 1400 rpm and 15% throttle it "lugs"?

Sorry for all the questions, I appreciate all your replies, but am looking for something a bit more detailed/theoretical/conceptual.
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Old September 11th, 2006, 20:07   #13
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Quote:
Originally Posted by Fix_Until_Broke
All good responses/descriptions of what is felt/conditions during lugging. Having the 0.681 5th and a lot of 40-45 mph driving during my commute, I'm familiar with the feeling.

Why does the engine do this? What causes the excess vibration, shuttering, noise, etc? What is happening in the cylinder(s)? Why is what happens more pronounced at lower engine speeds? Why when pulling a trailer up a hill at ~2000 RPM in 5th at 100% throttle and loosing RPM does this not happen (or I don't feel it) and with no trailer at 1400 rpm and 15% throttle it "lugs"?

Sorry for all the questions, I appreciate all your replies, but am looking for something a bit more detailed/theoretical/conceptual.
No that this helps...but I think lugging is bad for the motor mounts too.

Google might have some answers
http://www.google.com/search?hl=en&q...=Google+Search
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Old September 11th, 2006, 20:08   #14
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Default Engine lugging

Is when the car bucks and the engine shakes. Short of that, it's not lugging, but still, it is not advised to request lots of power where the potential to lug is great.

As to what is happening inside the cylinders to cause the motor to shake? Hmmm...good question.

Guess: the maximum amount of fuel that can be *safely* combusted depends on how much air is ingested. At slow engine speeds, there isn't much air. At light cruising this is perfectly fine since you are burning less than maximum fuel. As you reach that limit where load is greater than the amount of power you can generate (based on that fueling limit), the motor protests because it is basically being asked to run in reverse. The load (say, a steep hill) is acting to bring your motor to a stop...if you let it, it would bring your motor to a complete stop and then turn it in reverse (ignoring gearing and the physical possibility for this particular engine...some engines can run in reverse) as you rolled haplessly downhill, backwards, screaming in your rearview mirror. And, since you are not injecting enough fuel to argue sucessfully with the hill, it wins.

Think of arm wrestling...if you are not as strong or stronger than your opponent, he wins and your arm hurts from exerting effort but being overwhelmed by load.
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Old September 12th, 2006, 06:28   #15
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My opinion is that the condition is related to the duration of the combustion process within the cylinder and the amount of piston stroke possible in that amount of time at some given engine rpm.
At 1200 rpm the piston moves from TDC to BDC in .05 seconds. At 3000 rpm the time becomes .02 seconds. I believe the volume of fuel injected per stroke is related to the accelerator pedal command less than it is to the rpm signal. A foot on the floor acceleration request will have nearly the same fuel injected per stroke at 1200 as as 3000.
If that is true, then the pressure of the combustion is higher in the more slowly moving piston than in the faster one. The combustion event is in effect occuring in a more restricted volume. I believe the description of "lugging" is related to the relatively large combustion events in a more limited volume or in a shorter percentage of the piston's down stroke.
There are two quick resolutions to the condition: More piston speed (down shift for higher rpm) or less chamber pressure (reduce the volume of fuel injected by adjusting the accelerator pedal position).
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