my 300D is very slow off the start

Guest (MBNZ) · May 6, 2001

I just purchased a 1984 300D. The car is VERY slow from a standing stop but is fine on the highway. Does this tell me that the engine is losing compression? Does losing compression NOT compromise highway driving? Everyone tells me that the cars are slow but this seems ridiculous from a standing stop particularly on an incline. I have to foor it and patiently wait for the turbo-charger to take effect!

Guest (MBNZ) · May 8, 2001

Welcome to the world of diesels. Yes they are slow off the line. I get a good chuckle when I get in my pick up after driving my Benz for a few days. I start to accelerate at a light and lite the tires up. (I have padded the engine in the pick up a bit) At any rate, yes they are slow on start. It is just something you get used to. Good luck. Rick

Guest (MBNZ) · May 8, 2001

You don't have to floor the car, just be patient. For the last four years, all I have owned is a diesel, and you become a much better driver for owning one, but if you floor the car you will tear it appart. Try to find a happy median somewhere in there. Happy driving.

Guest (MBNZ) · May 12, 2001

Re: Re: my 300D is very slow off the start

dont floor it the car will hate u and make u pay check the fuel filters (pre and main) keep the fuel above half full dont let sludge get into the system warm the car up for 5 mins my exp. if that hasnt worked its going to cost deisels are made to burn down thw hwy not for dragging V8's louis

Guest (MBNZ) · Jun 1, 2001

Please ignore the first couple replies to your message! A 1984 300D should NOT be a slug off the line. That is often indicative of low compression or an injection pump that needs help. I believe a good running car of your year should go 0-60 in roughly 13-14 seconds. Find a flat stretch of road and check it with a stopwatch. If you are slower than 15-16 seconds, something is definitely wrong. I have driven many MB turbodiesels and it's amazing how poorly some run (low power) with the owner's weak excuse being, 'well, it's a diesel, it's supposed to be slow!' Nuh-uh, my friend, not true. Slow compared to a gas Benz, yes, but not a total dog. Try the stopwatch test and let me know what you find! One last caveat - if you live at high elevation, such as Reno or Denver, you're screwed: it will always be a dog. I live at sea level and it amazes me how much power loss there is off idle past about 4000 feet...

Dave M. 1987 300D - 226kmi 1983 240D - 201kmi

Guest (MBNZ) · Jun 18, 2001

Re: Re: my 300D is very slow off the start

 Having just read the last post; I felt it would be prudent to reread the original post as well as the subsequent to posts following. Having completed said task, I fail to observe where the second or third posts fail in the data they present. Perhaps Dave you would be so kind as to utilize your infinite wisdom and point out my failings in the following thought process: Original post: 'I just purchased a 1984 300D. The car is VERY slow from a standing stop but is fine on the highway. Does this tell me that the engine is losing compression? Does losing compression NOT compromise highway driving? Everyone tells me that the cars are slow but this seems ridiculous from a standing stop particularly on an incline. I have to foor it and patiently wait for the turbo-charger to take effect! Facts mentioned here: 1. Owner of car feels it is slow from a standing stop. 2. Car is new to owner 3. Owner feels car operates 'fine' at highway speeds. 4. Owner has to patiently wait for turbo-charger to take effect. Facts known to diesel operators: 1. Normally aspirated diesel engines do not increase rpms rapidly as in their gasoline counterparts. 2. Turbo-charged engines exhibit great increases in both horsepower and torque once the turbo-charger has progressed sufficiently through its boost band. 3. Amount of 'boosted' engine performance is directly proportional to the amount of boost applied to said engine. 4. Amount of boost developed is directly proportional to the velocity of the turbine in the turbo-charger. 5. Energy utilized to increase turbine velocity is drawn from increased amounts of exhaust gasses passing through the turbo turbine blades. 6. Increases in exhaust gas production are directly proportional to the increases in engine rpms. 7. Gear shifts made by a transmission directly affect the rpms of an engine. 8. Working (effectual) turbo boost attained in upwards of 2000rpms on engine. Based on the above data I believe the owner is describing an apparent lack of performance from his engine while they 'wait for the turbo-charger to take effect'. Lets see how this goes: 0 mph up to 2nd gear shift: 1. Engine starts ad idle 2. accelerator pressure applied 3. engine rpms increase 4. exhaust gas production increases 5. turbo turbine velocity increases 6. amount of turbo boost available increases 7. steps 2-6 repeat until up shift 2nd gear shift up to 3rd gear shift 8. transmission shifts to second gear 9. engine rpms decrease under load of second gear 10. exhaust gas production reduces proportionately due to decrease in engine rpms 11. energy utilized by turbo turbine reduced proportionately due to reduction of exhaust gasses 12. turbine velocity decreases proportionately due to decrease in available energy 13. boost decreases proportionately due to reduction of turbine velocity 14. 'boosted' horsepower decreases proportionately due to reduction of boost 15. engine rpms increase at a rate proportional to the current usable horsepower/torque.( inherent + current boosted horsepower/torque) 16. exhaust gas production increases 17. turbo turbine velocity increases 18. amount of turbo boost available increases 19. steps 15-18 repeat until up shift 3rd gear shift up to 4th gear shift: 20. transmission shifts to third gear 21. engine rpms decrease under load of third gear 22. exhaust gas production reduces proportionately due to decrease in engine rpms 23. energy utilized by turbo turbine reduced proportionately due to reduction of exhaust gasses 24. turbine velocity decreases proportionately due to decrease in available energy 25. boost decreases proportionately due to reduction of turbine velocity 26. 'boosted' horsepower decreases proportionately due to reduction of boost 27. engine rpms increase at a rate proportional to the current usable horsepower/torque.( inherent+current boosted horsepower/torque) 28. exhaust gas production increases 29. turbo turbine velocity increases 30. amount of turbo boost available increases 31. steps 27-30 repeat until up shift 4th gear shift on: 32. transmission shifts to fourth gear 33. engine rpms decrease under load of fourth gear 34. exhaust gas production reduces proportionately due to decrease in engine rpms 35. energy utilized by turbo turbine reduced proportionately due to reduction of exhaust gasses 36. turbine velocity decreases proportionately due to decrease in available energy 37. boost decreases proportionately due to reduction of turbine velocity 38. 'boosted' horsepower decreases proportionately due to reduction of boost 39. engine rpms increase at a rate proportional to the current usable horsepower/torque.( inherent+current boosted horsepower/torque) 40. exhaust gas production increases 41. turbo turbine velocity increases 42. amount of turbo boost available increases 43. steps 39-42 repeat until a change is made to accelerator setting Based on this data: A.) If one is able to maintain engine rpms at or above 2000 rpm through out ALL of the above steps, one can appreciate the full potential of a boosted engine without any lag in performance. B.) If one is not able to maintain 2000 rpm of their engine through out all of the above steps they will experience any and all reductions proportional to the time/distance out of the 2000 rpm range. Note: While driving my car, in anything other than sustained 50 mph cruising, I seldom stay in the 2000+ rpm range and as such have to operate with the energy available; which is of course dictated by the properties stated above and has no bearing on what I 'think' they should be. Seems like physics 101 Dave. Oh, by the way, Physics 101 also states 'you can't push on a rope'. Rick

Guest (MBNZ) · Jun 19, 2001

I stand by the original comments. The car should not be 'ridiculously' slow off the line (exact word used by original poster.) I can't tell you how many turbodiesel MB's I've test driven that were underpowered due to a mechanical problem of some sort, that the owner blew off as 'oh, they're all slow... just get used to it.' Not true. You figure this out only after driving one that is operating properly, and realize that the others had problems. Like I said before, the stopwatch test is the only accurate test. If the 0-60 time is close to MB factory specs (as stated in the TDM) then the car is running as it should. If not, something is wrong. Simple as that... BTW, if you never exceed 2000rpm except on the highway, you need to squeeze the pedal a little more! Normal acceleration on my turbo is watching the rpm's pop to ~1800 off idle, and then sweeping from 1800-3000 and staying in that range through each gear at part throttle, which results in healthy forward propulsion. There should not be a 'kick in the rear' from a turbo 'spooling up'. It should be relatively linear. But, it's all relative and subjective, which puts me right back to the stopwatch test. Oh, one last thing - you never mentioned what year, make, model you have... Best regards, Dave M. Physics 101 1987 300D - 226kmi

Guest (MBNZ) · Jun 19, 2001

Re: Re: my 300D is very slow off the start

David, 1. If you check I did not say I 'never exceed 2000rpm except on the highway'. 2. I do not argue your statement 'I believe a good running car of your year should go 0-60 in roughly 13-14 seconds.' I merely presented the factual progression of properties these engines undergo while operating so as to explain why a 300D with a turbo, or any turbo equipped motor, does not act 'boosted' whenever the engine is operating. As I stated; 'A.) If one is able to maintain engine rpms at or above 2000 rpm through out ALL of the above steps, one can appreciate the full potential of a boosted engine without any lag in performance.' To explain what one can expect when the engine is not maintained as stated above I also stated; 'B.) If one is not able to maintain 2000 rpm of their engine through out all of the above steps they will experience any and all reductions proportional to the time/distance out of the 2000 rpm range.' Your driving habits are just that and are of no concern to me. My driving habits are mine and I choose to allow the engine to operate under the 2000 to 3000 rpm range while accelerating when it is warranted. BTW Yes turbo boost is as linear as the inputs affecting are. Regards Rick 1985 GMC Pick-up 383 Stroker powered 1982 300D turbo 1966 TR4A IRS 1966 TR4A LA

Guest (MBNZ) · Jun 20, 2001

I think where we are miscommunicating (the most, anyway) is on your 2000 rpm statement. My point was basically this: When driving a turbodiesel Benz, the RPM's are almost NEVER below 2000rpm when accelerating (light OR heavy acceleration.) At idle, yes. At low speed cruising, yes. But when accelerating? Due to the function of the transmission's torque converter, it rarely lets the engine go below 2000rpm under anything but extremely light throttle application when accelerating. Which, if you consider this, keeps the engine into 'boosted' territory when accelerating nearly all the time, except perhaps the *very* first part of first gear, and even then the engine will have enough normally aspirated power to motivate the car off the line without twiddling it's proverbial thumbs. And I understand perfectly the operation of a turbodiesel engine, btw... I *do* own one! One point to consider: The engine does not pick up power from the turbo based only on RPM. Throttle position has a LOT to do with it. You have to be at or over ~2000rpm AND have your foot into the throttle. If you have never done so, attach a boost gauge (a cheap fuel pressure gauge that reads to 10-15psi works OK) to the ALDA boost line and run the hose out the hood seam and through the window. Go drive the car while observing the boost pressure. You'd be surprised at how and when the needle moves. This also serves to tell you if your car is reaching max boost, which is adjustable at the turbo. It should be just under 1 bar (~14.5psi) at max load, high RPM. If it's below this you can adjust it and pick up some 'free' horsepower!

Regards, Dave M.

Guest (MBNZ) · Jun 21, 2001

Re: Re: my 300D is very slow off the start

Dave, You might try this: Drive in city and suburban traffic and maintain the pace the traffic sets, ie don't set the pace. While driving this way monitor your tach. You may be surprised at the amount of time you spend below 2000rpm and therefore below full boost. I simply wanted to state the reason why these autos do not act boosted all the time and seem sluggish even though they are turbo equipped.

Regards Rick

Guest (MBNZ) · Oct 26, 2001

I know EXACTLY what you mean. I just bought an '84 300D a week ago. I KNOW diesels are slow (eh hemmm Rick-n-Seth), I also own an '81 Jetta diesel, but this situation is like letting your food off the brake of a gas car at high idle and letting it creep up to speed. Once I get to about 2300 rpm, she performs just fine. I rode around in a 300CD for a few days several years ago, and it wasn't like this. At least we were able to run in city traffic. I will change the fuel filters as Dave recommended, but I hope it isn't anything serious. This engine was said to have been rebuilt some 100kmi ago.kew1-ch50.geneseo.net

Guest (MBNZ) · Mar 4, 2002

Completely new idea (hopefully helpful)

I'm an 18-year-old who has only owned one car in his life, and that one car he's only owned for about 8 months. It's a 1985 300D, (turbocharged), and it's almost as old as I am. Recently, I changed the oil in the car (it was overdue) and found to my dismay that the car was literally a DOG out on the road. When it was on the highway, it would cruise at 75, but I feared every hill I approached!! As it hit a hill, it would start to slow down, and all sense of pull would simply cease. The engine just CREPT when it had to accelerate against an uphill OR its own weight. Turns out I overfilled the crankcase by about a half-quart when I added the new oil. As a result, my 0-60 time (which is usually about 13 seconds) was up around 18 seconds, and it wouldn't even GET to 60 if I were on a slight incline. I understand it's really dangerous to have too much oil in your car, and I felt REALLY stupid once I was alerted as to what the problem was. Check your oil. If it's even slightly overfilled, climb under your car and let a little out. Make sure to keep the dipstick between half-marker and full-marker, but don't let it drop below and most CERTAINLY don't let it go over, or you'll be dealing with a turbocharged slug, and be vulnerable to transmission and engine damage. -Jerrold 18 years old -Mercedes 300d 17 years old just trying to help.

Guest (MBNZ) · Mar 5, 2002

Re: my 300D is very slow off the start - update

This is an update since my last post in June 2000. Since then, I bought a fixer-upper '87 300D (which I still have), a 1983 300D (which was totaled), and a 1984 300D to replace the wrecked one (wife's car). From what I've learned, the problem is VERY likely to be the ALDA adjsutment. My 'project' 87 is a rocket off the line. The 83 was so-so, but not bad. The 84 had the ALDA adjusted by the PO and it also gets off the line quickly. 
 
Now, my other 87 was so-so off the line, not nearly as snappy as the fixer-upper I got with the same engine. While doing the head replacement job (long story), I pulled the injection pump to have it calibrated. The shop said it was off from specs, a little low on fuel delivery - which was why the power was down. They got it set properly. I asked about the ALDA and they said the proper way to adjust it is internally on the I/P, but you can remove the 'tamper seal' on top of the ALDA and do it there. The car isn't yet reassembled so it hasn't been test driven since the I/P calibration. 
 
WARNING: I have heard that there is a slight (10-20%) chance that by adjusting the ALDA, it may break internally. It's not available separately. Just FYI. Anyway, the URL below shows a photo of the ALDA with the tamper cap removed with pliers. I did this on my sister's 87 300D (yeah, we like them W124 diesels!) I loosened the locknut and turned the setscrew 1 turn counterclockwise. It made a very noticeable difference in off-idle power! I actually need to adjust it a bit more, haven't had time though. Basically you adjust it until the power is good. If the car smokes, you went too far (too rich), back it off a little. I've been told that most require 1-1.5 turns CCW. 
 
Now, the PROPER way to fix this is to remove the I/P and take it to a Bosch shop for a bench recalibration (~$150-$200). But, if you're feeling lucky this trick may do the same thing for free. On a W123 it's simple, on a W124 you have to remove the intake manifold to access the ALDA - very annoying. Also, there is a little-known procedure in Mercedes dealers Workshop Information System that documents this, although they recommend a 1/4 turn, and that just isn't enough. 
 
Note: This applies if your car runs good otherwise, and has 'normal' power above ~2000rpm, when the turbo is producing boost. The ALDA adjustment basically is setting the fuel quantity minimum setting. If you have other problems, this won't cure them. 
 
 
Hope this helps some of you out there!

Dave M. 
Sacramento, CA 
1987 300D - 229kmi (recalibrated I/P, new head) 
1987 300D - 237kmi (project, needs new head) 
1984 300D - 207kmi (wife's car) 
1981 VW Dasher diesel - 170kmi (beater) 
 
1983 300D - 30xkmi (totaled) 
1983 240D - 204kmi (sold) 
1990 300E - 75kmi (sold) 
Plus four previous Dasher diesels and other misc...

Guest (MBNZ) · Apr 3, 2002

Err, I'm having a different problem here. My 1985 300D has, over the winter, gotten SEVERELY underpowered in the 2500+rpm range. The turbo kicks in, and pulls for the next 500rpm, but if you try to go any higher than about 3000rpm, power is GONE. When I floor it, and it downshifts, the car tends to DECELERATE in the 3500-4500rpm range, which I KNOW is wrong because it didn't do this last fall, before winter. I realize that winter starting and driving can be tough on a diesel, and I hope that something just got knocked out of adjustment or clogged or SOMETHING that doesn't mean that I lost compression or something terrible with my engine. Any ideas would be appreciated. I want to get my 0-60 back down to 14 seconds, because right now it's closer to 18. -Jerrold

Guest (MBNZ) · Apr 3, 2002

Re: Some one had to day it

Dude, your car has 230K on it, coupled w/ the fact that it is a 617 engine. It's not supposed to be fast on or off the line.

Braingears · Aug 13, 2002

Diesel run better when run HARD!

Diesel run better when run HARD! This is a common mistake people make. By running the engines harder, it keeps the cylinders and injectors cleaner. YOU WILL NOT HURT THAT DIESEL! Something that will help is add a quart of ATF to the fuel ever 3 to 4 tanks. You will notice a diference immediately. This helps loosen up the seals again and breaks free additional carbon. This will not hurt the engine at all.

Also read the posting on bypassing the Turbo to Injection Pump emmisions valve. This is probably broken or clogged.

Chuck

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Chuck Fowler
"You can't kill em"
'74 240D - 359,000 Miles
'76 300D - 350,000 Miles
'84 300CD - 280,000+
'85 300D - 380,000 Miles
'87 300D - 225,000+ Miles

dave1shere · Nov 2, 2002

How do you ADJUST TURBO BOOST

Hello Everyone,

I am new to this site. Have a 1985 300D. I seem to have the same problem.

How do you adjust the Turbo Boost to maximize performance?

Thank You,

Dave E.[?]

zekey · May 17, 2003

I had this problem too ...

I have a 300TD Wagon that would not go. I found the filter (screen) in the gas take was stopped up. I pulled the tank and had it cleaned and replaced the filter. That solved the problem! Good Luck.

dfwdiesel · May 23, 2003

I bought a 1984 300D Turbo, It is much faster then my
78 300D and 83 300D non Turbo. The ...

I bought a 1984 300D Turbo, It is much faster then my
78 300D and 83 300D non Turbo. The engine is quite strong, starts easy even at 20 degrees. But what helped acceleration. I put a transmission in and carefully adjusted the cable that determines how long
the car stays in gear until the next shift, and when it kicks down. I have it set at a little more the 4,000 rpms floored. Not sure if this is correct, but I like it enough to pland a paint job for the low mile
faded paint California car. Even the non turbos are not that bad with clean filters, good oil, valves adjusted etc, even differential oil fresh makes a difference.

There can be a big difference in the same model diesel, I run mine hard, it loosens them up and gets better performance.

I bought a sluggish high miles 85 190D, daughter has
a low miles 85 190D. After a few months she was shocked to see which one was smoother and faster.

Maintain it well and drive it like you just stole something!
John Gregg

my 300D is very slow off the start

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