Subject: Mercedes 300D turbo, 1984, 40mph tops, diagnosis?


I will do my best here. Please ask if I have been vague anywhere. Feedback welcome, desperate. Will attempt fast reply. Chilton's manual coming in mail,
will be working on car end of the week.

Car has gradually lost power over 2 ys time, used to reach 80mph, now only 40 on a hot day. Had a compression test 8 ys ago, (400, 380, 380, 340, 340, , 280). What can I draw from this data? Looks bad to me. Car starts great, engine sounds fairly good, revs good, 3.5k rpms when not in gear except: surges some times when in gear when maxed out, missing some I think, won't get over 20mph on cold morning for at least 20 minutes, dead on hills. Does NOT smoke! Engines sounds pretty good when it has no load on it, but hills, load etc and it is a slug.

I have 2 injectors off, all hoses off, modified 27mm wrenches to fit. Seems quite rusty in both injectors, discolored redish with flakes of material floating about. Metal jets look clean enough.
Blowby test seems strong. Someone suggestion strongly that it was a vacuum leak?

Main issue - Seems vastly underpowered, though accelerates up to 20 fairly well, but when cold, will not go above 20.

Should I go forward with, ( AND in what order?) replace fuel filter (s), (air filter seems good), injectors, Fuel pump (cringe, $400 to test if I remove, $900 to rebuild).

My stance - Had car 2 years as project, now may sell. Previous owner had minimal records of work. paid $1900, love these models to drive, had two now but student loans require I be shrewd, not romantic with cars at this point. I will unload it if it means high inputs over $1500. New injectors $150 each x7=$750. will be working on car end of the week.

Thank you sincerely for any help.

- Lev

ph# 7072289554

- "No car is as expensive as a cheap Mercedes"

I'd do the fuel filters first. They are cheap and would give many of the symptoms you describe.

Does the transmission shift properly, i.e. at the correct rpms, not too soon?

I just drove an 83 240d auto from Vermont to Ontario and the previous owner said it had no power and would only 25mph up hills. Turns out the engine is sweet, but the auto box gets into top gear by 20mph and therefor has no "get up and go". Manually shifting my car makes it go full speed up hills.

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I choose to be happy, even when the Mercedes is being awkward, lol

Make sure all the linkage is operating properly, esp. the rubber bushing on the fire wall.
Sounds you're not getting the fuel you need and the turbo is not kicking in. Make sure the filters have been replaced. How old is the fuel? You say this has taken a long time to gradually get to where you are.
Have your injectors tested, usually the nozzles fail first, not the whole thing, so no need to replace good parts.
Check the ALDA lines, http://www.dieselgiant.com/mercedesaldaboostsystemservi.htm
Keep the fuel (Injection) Pump as a last resort. You'll want to make sure it is timed correctly, as in timing chain stretch.
There are many avenues to go down before you do that, try a search or two.
Good luck and keep us informed.

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83 SD

84 CD

definately replace the fuel filters, this sounds like a fuel starvation problem. also check the tank screen, and all fuel lines for leaks. you may have an air leaking into your fuel lines which would cause the same problem.


another thing to check is the PCV system (positive crancase ventilation). if one of the lines for this clogs up or kinks, you will have serious problems with power, and could build up enough pressure in the crankcase to blow seals..


this seems like an easy fix problem. i don't want to get your hopes way up (just in case) but i'd start with the small, and most importantly, cheap fixes first.

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http://i106.photobucket.com/albums/m...73378_30-1.jpg

Vacuum problem on a diesel? Hardly. Have you adjusted the valves?

If this is the case, the engine will stop or blow one of those hoses.

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83 SD

84 CD

I'll third or fourth fuel filters or tank screen.

Lev,
Welcome to the forum!!
Looks like the general consensus is (& I agree), Replace the filters, Both the secondary canister & the plastic primary. If your tank is nearly empty, it would be worth cleaning the tank strainer.
After you have done that, please message us back on here with what change occurred (if any).

For now I would put injector & IP work on hold, its very unusual to have what you are seeing caused by bad injectors unless some one has had them in pieces & then all bets are off, IP problems are most likely to be not getting full throttle, linkage adjustment, not IP rebuild.

Is your turbo working? Can you hear it wind up? Just a thought, if its jammed, it will stop the motor revving much.

Looking forward to hearing how you go with the filters.

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Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

You have 6 compression numbers... in an 84 300D...

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Could that be described as too much compression perhaps?

Linkage problems are all too common. Have someone press the fuel pedal and observe if the stop on the injection pump is reached by the pump arm.

Air in fuel lines, fuel filter, etc all seem like good, relatively cheap fixes. When is the last time you checked your air filter/ connections? Nick said it sounds like a either fuel starvation or air in fuel lines, i would say it could also be not enough air. Good luck, let us know how it turns out!

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In the Garage:
'84 300SD, 85K "The Princess"
2011 BMW 328I XDrive, DD

Thanks folks ~

I'm working all week, but all over it on weekend, and will report back. Lots of good advice here, and a few things to neg of the list, so my sincere thanks. I have don't very little work on the car, and so I can't say about when things were replaced, few records kept from previous owner. Oops! Yeah, I doubled up listing the 340 reading.

Ok, I got more attention than perhaps I deserved, and definitely expected, so again, my thanks. Lets see what I can do with it...

Fuel filters
Clogged screen in fuel tank
Fuel tank vent
Throttle linkages
Throttle End-Of-Travel adjustment backing out so as to restrict full throttle

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Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

Replace your air and both fuel filters. Clean the banjo bolt that has the line coming out of the intake. Check all your linkages. Make sure you are getting full movement when you press the pedal. When you press the pedal to the floor you should max out the linkages. There is a throttle stop on the rear of the injection pump. Make sure that is hitting when you press the pedal to the floor. Make sure the all ball sockets on the linkages are clean and lubed, as well as all the pivot points. Check the throttle bushing on the fire wall. It's what translates the pedal movement to the linkages. Valve clearences aren't going to hinder you that much. While is should still be done, especially if it hasn't been done in a long time, I wouldn't expect it to limit you to 40mph. Also make sure you shift points aren't too low. If the car is shifting through the gears way too fast it will make it extremely hard to excelerate. You can adjust this with the bowden cable which is attached to the linkages on the valve cover.

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Ok, big help ya'll. Car is running cherry, and I'm an idiot with very clean cylinders. Took them all out, cleaned, replaced hoses, fuel filters, and she has full power. Must have been the filters. My warmest thanks to all who commented.