What is Engine Lugging?

Fix_Until_Broke

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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?
 

MrErlo

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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.

Fix_Until_Broke said:
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.
 

wjdell

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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. :)
 

Bob_Fout

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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.
 

MrErlo

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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.
 

Brock_from_WI

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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?
 

Bob_Fout

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MrErlo said:
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?
 

TurboBenz

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Bob_Fout said:
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).
 

Bob_Fout

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TurboBenz said:
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.
 

wjdell

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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.
 

40X40

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Lugging an Engine......

http://www.cartalk.com/content/columns/Archive/2005/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
 

Fix_Until_Broke

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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.
 

Bob_Fout

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Fix_Until_Broke said:
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=what+is+lugging+an+engine&btnG=Google+Search
 

nicklockard

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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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Lug_Nut

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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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gdr703

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Lugging is a condition where the power required is more than the power available from the engine.

Typically in a gasser this is stated as “keep the revs above 2000” Most 2litre gassers have 30hp available at 2000 rpm. The TDI has 30hp available at 1300rpm. Therefore the equivalent statement for the TDI is “keep the revs above 1300 rpm” to avoid lugging.
When slowing down keep the car in 5th until the rpm’s are less than 1000 rpm, then change down, as this will minimize the engine braking effects. When driving on a flat road, with only the driver in the car it will pull in 5th from 1100 rpm without lugging, and on a downhill even at lower rpm. Get to know your cars capability in this rpm range. If your engine is not running smoothly at these rpm's and power demands, then its most likely your fuel, try some fuel additive.
But, don’t forget to exercise the car from time to time through the whole rev range. Say once a week, when accelerating on a highway on ramp, hold second gear and stomp on the go faster pedal and let the rpm go through to the top. It blows out a whole bunch of crud, and keeps the engine sweet. The engine responds well to a touch of variety.

By the way, the 90HP TDI can produce 19HP at 1000 rpm, 30HP at 1300, 41HP at 1500, 56HP at 1900, 71HP at 2500, 82HP at 3000, 87HP at 3500. - thats very different when comparing to a gasser, and makes the diesel very difficult to lug.

hth
 

TurboBenz

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Bob_Fout said:
1500 RPM, 5th gear. Try and accelerate at a reasonble speed. Feel and listen to the motor.
I go around town at 1500rpm in 5th all the time (80kph). Obviously if you really need to get on it you should downshift, but other than that you can accelerate with the flow of traffic just fine. In real world driving you can be at 1500 and accelerate (on relatively flat ground) with the flow of traffic just fine IMO.
 

Bob_Fout

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TurboBenz said:
I go around town at 1500rpm in 5th all the time (80kph). Obviously if you really need to get on it you should downshift, but other than that you can accelerate with the flow of traffic just fine. In real world driving you can be at 1500 and accelerate (on relatively flat ground) with the flow of traffic just fine IMO.
Yes, maybe in slow traffic, but not around here where there is not much traffic (and folks then go faster)...if you don't go you get run over :D
 

Fix_Until_Broke

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Lug_Nut said:
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).
I looked (breifly) to see if the speed of combustion increased with cylinder pressure - Don't know I guess either way - similar occurance. With a fixed rate of combustion, additional fuel would provide a higher pressure over the same duration at a constant RPM - which would create the noise/vibration. It does not happen at higher RPM's because the pressure expansion is spread out over more degrees of crank rotation. I'll need to think it through a couple (dozen) times. Maybe if one could slow down the burn rate (lots of EGR? or multiple injection events?) the conditions where lugging occurs could be at a lower RPM.

I think your times actually should be 0.025 and 0.010 seconds respectively

1200 rev/min = 2400 strokes/min divide by 60 sec/min = 40 strokes/sec = 0.025 seconds/stroke. Minor detail in regards to this topic

I'm not sure I agree with the thoughts relating to power required vs power delivered, if that's the case then we are all always "lugging" as the the power requested versus the power delivered is always crossing from positive to neutral to negative at all sorts of rpm's

Good discussion, this is what I was looking for - Thanks

Lets keep it coming - any more thoughts on this?

Oh I wish I had a cylinder pressure measurement sensor and an oscilliscope, although I'd definately be a traffic hazzard.
 

MrErlo

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Fix_Until_Broke said:
With a fixed rate of combustion, additional fuel would provide a higher pressure over the same duration at a constant RPM - which would create the noise/vibration. It does not happen at higher RPM's because the pressure expansion is spread out over more degrees of crank rotation.
so with my Sprints and NOT having any chip tuning done, would i experience lugging at higher RPM? i had my IQ adjusted up to 3.4, but as people have pointed out in other threads, for some reason people have been unable to adjust it up high enough to completely eliminate the idle shudder. would this help explain why i seem to be noticing lugging at higher RPM than other people? and as a solution... would RC2 (or any chip tuning) help to eliminate both the idle shudder and the higher RPM lugging?

i'm not worried that i'm damaging my engine, i know when my car will lug and i simply avoid it. i'm just thinking of another way to justify RC2 besides the WHEEEE!!!1
 

gdr703

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Fix_Until_Broke said:
I'm not sure I agree with the thoughts relating to power required vs power delivered, if that's the case then we are all always "lugging" as the the power requested versus the power delivered is always crossing from positive to neutral to negative at all sorts of rpm's
What I meant was that the engine is not capable of delivering adequate power to maintain rpm.
If the engine is capable of pulling away, ie increasing rpm, no matter how slowly, then it is not lugging, simply working hard.

hth.
 

Fix_Until_Broke

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gdr703 said:
What I meant was that the engine is not capable of delivering adequate power to maintain rpm.
If the engine is capable of pulling away, ie increasing rpm, no matter how slowly, then it is not lugging, simply working hard.

hth.
So when I'm at 3000 RPM in 4th (~65 mph) at 5000 lbs up a 8% grade and dropping rpm's because I only have 90 HP, Is that lugging? It's not making the same vibrations/sounds that it does at <1500 rpm in 5th (or any other higher gear) when you lean into it too much.
 

Mike_M

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MrErlo said:
so with my Sprints and NOT having any chip tuning done, would i experience lugging at higher RPM? i had my IQ adjusted up to 3.4, but as people have pointed out in other threads, for some reason people have been unable to adjust it up high enough to completely eliminate the idle shudder. would this help explain why i seem to be noticing lugging at higher RPM than other people? and as a solution... would RC2 (or any chip tuning) help to eliminate both the idle shudder and the higher RPM lugging?

i'm not worried that i'm damaging my engine, i know when my car will lug and i simply avoid it. i'm just thinking of another way to justify RC2 besides the WHEEEE!!!1
I think low-speed "shudder" and "lugging" are probably two distinct phenomena. People who have installed the PD lift pumps in their VEs have reported better low-speed performance and a lack of shudder.

In your case, it may be nothing more than the "sucking" side of the injection pump being unable to keep up with the fueling demands at low RPMs with the bigger nozzles.

If you want to eliminate the shudder, try installing a PD lift pump. It won't help answer questions or settle the debate about lugging, but it should make the shudder go away. :D

Mike
 

Mike_M

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gdr703 said:
What I meant was that the engine is not capable of delivering adequate power to maintain rpm.
If the engine is capable of pulling away, ie increasing rpm, no matter how slowly, then it is not lugging, simply working hard.

hth.
That, too, is the definition I've seen in various places. It's not "power requested" but "power required" vs power delivered.

As the theory goes, if you can't make the power required to accelerate, you're lugging.

Fairly unscientific and unsexy definition, but if that's what it really means...*shrug*

Mike
 

MrErlo

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PD lift pump

Mike_M said:
If you want to eliminate the shudder, try installing a PD lift pump. It won't help answer questions or settle the debate about lugging, but it should make the shudder go away. :D
this is kind of a rush post, but i found this
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=190028610452&ssPageName=ADME:B:WNARL:UK:12

form this thread
http://forums.tdiclub.com/showthread.php?t=151214&highlight=pd+lift+pump

is that what i'm looking for? or, has anyone got a link to a How To or a link to someone who sells the part?

also, will this provide any other benefits besides eliminating shudder? i've been told that will go away when i get RC2 done. hope this isn't too bad of a hijack, thanks.
 

CaJones

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Lugging is pretty well described by lugnut and GDR... It is the inability of a combustion engine to do the work/ pull the load requested of it without enough margin between actual load and peak load the engine is capable of.
It's usually observed when asking the engine to do too much work/acceleration at a low rpm in a higher gear, where change or increase in rpms is low, nil, or decreasing, at medium to high throttle settings.

You are asking the engine to do too much work in a low rpm range that it makes a definite oscillation / sound in the process that it does not make in almost all other normal operating conditions.
 

Mike_M

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MrErlo said:
this is kind of a rush post, but i found this
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=190028610452&ssPageName=ADME:B:WNARL:UK:12

form this thread
http://forums.tdiclub.com/showthread.php?t=151214&highlight=pd+lift+pump

is that what i'm looking for? or, has anyone got a link to a How To or a link to someone who sells the part?

also, will this provide any other benefits besides eliminating shudder? i've been told that will go away when i get RC2 done. hope this isn't too bad of a hijack, thanks.
Looks like that might be the right one. I dunno if I'd buy one off eBay, though.

Here's the original thread. I don't have time to check right now, but it might have the part number for the correct one somewhere in there.

http://forums.tdiclub.com/showthread.php?t=93212

...and here's a link to it on Kerma's site:

http://www.kermatdi.com/servlet/-strse-42/In-dsh-tank-lift-pump/Detail

Mike
 

nicklockard

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Fix_Until_Broke said:
So when I'm at 3000 RPM in 4th (~65 mph) at 5000 lbs up a 8% grade and dropping rpm's because I only have 90 HP, Is that lugging? It's not making the same vibrations/sounds that it does at <1500 rpm in 5th (or any other higher gear) when you lean into it too much.
No, that means you have a bad MAF! If you can't maintain 65 mph up a grade in fourth at 3000 rpm, your MAF is totally shot. I can zip up that same grade in fifth at 2650 rpm's on cruise control easily.
 

Fix_Until_Broke

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nicklockard said:
No, that means you have a bad MAF! If you can't maintain 65 mph up a grade in fourth at 3000 rpm, your MAF is totally shot. I can zip up that same grade in fifth at 2650 rpm's on cruise control easily.
Attach a 2000 lb 7 foot tall trailer and let me know how that goes for you:rolleyes:
 

nicklockard

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What does this mean:confused:

Clarify...you've got me confused: how does that last comment relate?
 
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