suddenly sluggish 1985 300td - Mercedes-Benz Forum

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post #1 of 11 (permalink) Old 10-15-2010, 08:00 PM Thread Starter
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Date registered: Oct 2010
Vehicle: 1983 300tdt
Location: western edge of sacramento valley
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suddenly sluggish 1985 300td

hello there !

im new to forums in general and to diesel ownership - but after doing some research here and elsewhere online, im confused.

i bought this car less than a month ago - have filled the tank three times maybe - and never put in any additive.

last night while i was driving home, all of a sudden, i lost all power at the low end.

the car shifted through 1,2,3 gears prematurely and the rpms stayed low

on a long straight away, i could get it to normal rpm and about 50 mph, but not much above that

my 17% grade driveway posed the biggest issue

i finally made it up - no smoke, just real sluggish movement

i bought a secondary fuel filter - but can figure out how to replace it - i cant even find it in the engine and could not find anything online to point me in the right direction

the clear plastic fuel filter looks clean - but there is an air bubble in it about .5 inches x appx 1 inch -

i pumped the white thingy (primer pump) and tiny air bubbles formed, but did not add to the volume of the "larger" air bubble described above

i have read about algae - i live in a very warm climate though - don't think that is the issue if the clear fuel filter is clean of debris

so, i guess im asking if anyone can direct me to the location of the current secondary fuel filter - i plan to fill the new one with diesel fuel from the tank - siphon it from the tank and fill that filter before screwing it on to minimize the amount of pumping necessary to avoid air lock

can anyone help me?

thanks - glad to be able to post these questions

any help is appreciated.
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post #2 of 11 (permalink) Old 10-18-2010, 01:16 PM Thread Starter
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im not sure if its allowable to reply to one's own post - but ive done a little more reading and feel like the issue might be air. ive also come to understand that the vacuum transmission system is very confusing

does anyone have a clue how i should get started?

again, thanks for any help
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post #3 of 11 (permalink) Old 10-18-2010, 01:56 PM
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Date registered: Sep 2010
Vehicle: 1985 300SD, 1985 300D, 1981 300TD
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Well, I'm no expert, but I think I can help with finding the secondary fuel filter. In the photo, you can see the silver Bosch fuel filter. I forget what size it is, but you will need to loosen the nut on top of the unit and the filter will then drop down. I don't recommend using an adjustable wrench. Put some rags under there to catch any fuel that spills when removing the filter.
You can see mine has fuel leaking on top where the nut is.
Hope this helps!

Mike
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post #4 of 11 (permalink) Old 10-18-2010, 02:26 PM
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YEAH. Change the main fuel filter to start with. Don't fill it with contaminated fuel like lot of owners do. The injectors might not like it.
Put it on dry and there should be a bleeding screw, or connector on the top. (its been few years since I sold my W123). With the bleeder open, pump the hand pump till all the bubbles clear. The engine might still require lot of turning before it will clear the line, so have battery charger ready.
If the new filter will not fix the low performance, next thing I would check is turbo.
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post #5 of 11 (permalink) Old 10-18-2010, 02:34 PM Thread Starter
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thanks very much - i will change the secondary fuel filter first - found some diy sites that describe the vacuum system, things to look at -

i really didnt want a project car, but i guess that is what ive got


as far as hand pumping, im afraid of air locking the engine

what if i purchased some diesel fuel specifically for the purpose of filling the new filter before installing it to reduce the amount of pumping necessary and the chance of airlocking??
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post #6 of 11 (permalink) Old 10-18-2010, 03:18 PM
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Originally Posted by pcalt View Post
what if i purchased some diesel fuel specifically for the purpose of filling the new filter before installing it to reduce the amount of pumping necessary and the chance of airlocking??
DON'T.
Check the prices of new injectors if you still want to consider it.
The hand pump is there for a reason. Newer diesel don't have it, but than the priming pump is more advanced and will bleed the air with some cranking. I found pushing the car nose down on my driveway very helpful in bleeding the air from the system. On your diesel you have easy access to injector lines, so cranking couple of them 1/2 turn will help in getting rid of air.
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post #7 of 11 (permalink) Old 10-18-2010, 04:02 PM Thread Starter
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Originally Posted by Kajtek1 View Post
DON'T.
Check the prices of new injectors if you still want to consider it.
The hand pump is there for a reason. Newer diesel don't have it, but than the priming pump is more advanced and will bleed the air with some cranking. I found pushing the car nose down on my driveway very helpful in bleeding the air from the system. On your diesel you have easy access to injector lines, so cranking couple of them 1/2 turn will help in getting rid of air.
thanks for that suggestion - any way you could post a picture of the injector line is?

im sure i can find it with a little help


NOTE: ***** new clue *****

i just got home, started the car up before doing anything. i had never tried to "revv" the engine while at idle - so i did that

i inoticed that the rpm's did not rise above 1000

does this indicate more of a fuel flow problem? and if so, does anyone have an opinion as to whether this is a secondary fuel pump issue or a tank mesh/screen issue? maybe the manifold (is that the right term??) isnt opening when i depress the accelerator??

thanks again for your interest here, i appreciate any and all help
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post #8 of 11 (permalink) Old 10-21-2010, 09:38 AM Thread Starter
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bump :)

seems as though i self diagnosed the problem - related to the accelerator pedal

i only fixed it last night but then it got dark so i didnt test drive

ill peek in here and see if anyone is interested in the solution to my problem

fingers crossed - home by four today - looking forward to confirmation of the solution

thanks to those who had input.

-pcalt

im sure ill be back to ask more questions in the future
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post #9 of 11 (permalink) Old 10-21-2010, 09:49 AM
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So you are saying that the carpet stopped gas pedal?
Where did I hear this one before?
Still replacing main filter if you don't know its status is good idea.
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post #10 of 11 (permalink) Old 10-21-2010, 12:11 PM Thread Starter
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Originally Posted by Kajtek1 View Post
So you are saying that the carpet stopped gas pedal?
Where did I hear this one before?
Still replacing main filter if you don't know its status is good idea.
no sir, the carpet had no involvement
i did not replace the plastic filter - it seemed new and the fuel clean - though i should have one on hand

i replaced the secondary filter before doing anything else - took a while as i am tool and time deficient

what happened is i sat in the car with the hood open and noted the movement of the steel rods - i stopped the car, played with those rods manually - noted that they move much further when i did it by hand than by foot in the cabin

so i traced them back and noted that the "turbo diesel accelerator linkage firewall mount" seemed to have delaminated - i.e. the rubber (?) bit between the two steel plates was spreading rather than staying together as a unit - so i figured the range of motion was limited by that - wrapped wire around it, started the car and pressed the accelerator with a decent range of motion and appropriate rpm response on the tach

i did not put it in drive or reverse as it was getting dark and i had an exam scheduled today - my fifth exam in a matter of 9 days

when i get home, i will drive it around my property to note if the transmission is shifting gears properly - my fingers are crossed

if the problem seems rectified, i will replace the turbo diesel accelerator linkage firewall mount

thanks for your interest

-pcalt
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