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300D turbo idle shake- end of my rope

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I have owned my 1984 300d for 11 years. I bought it at 120,000 miles and it currently has 160,000 miles

I change the oil every 1,500 miles and it is my daily driver. I’d say it’s a 9/10 condition, never run on biodiesel etc. it gets everything it needs.

about a month ago I started to notice a shake at idle when the engine is hot.

I don’t know what to do anymore. I replaced a bunch of stuff but still shaking. Power delivery is good and engine smooths out off idle

I have replaced:
  • Fuel filters
  • Fuel primer pump
  • Diesel purge
  • Rack dampener pin replaced and adjusted
  • Motor mounts
  • Rebuilt injectors (2x and pop tested)
  • Adjusted valves-camshaft is pristine
  • Timing chain feels tight on sprocket
  • Very little to no “cap dance” on blowby test
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· Registered
1976 450SL, 1992 190e 2.3, 1984 300D turbo, 1966 VW bus
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1,819 Posts
Discussion Starter · #2 ·
The above items helped but the shake is still there. What else is left?
I’m out of ideas and don’t know what to do.
 

· Registered
W123 300CD, W123 300TD, W202 C250D Turbo
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991 Posts
Wow - That was a lot of shake before doing the injectors. What happens if you undo each line while running ? Is the impact equal ? Just thinking about the delivery valves on the IP.
 

· Registered
1976 450SL, 1992 190e 2.3, 1984 300D turbo, 1966 VW bus
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1,819 Posts
Discussion Starter · #5 ·
Wow - That was a lot of shake before doing the injectors. What happens if you undo each line while running ? Is the impact equal ? Just thinking about the delivery valves on the IP.
Yes, when you unscrew each injector one at a time it seems pretty equal.
Each cylinder is definitely firing
 

· Registered
1982 300D Turbodiesel (US Spec)
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483 Posts
I had (still have, but not to that degree) a similar issue in my 82 and did all you did without much change.

In the end the vibrations improved after installing new vibration shocks and mounts and letting the new engine mounts settle. The shake is still there although you really have to focus on it to notice it.

After doing all that work and talking to a few diesel owners, I concluded the problem is the injection pump itself. After so many miles and especially hours of idling, the pump has worn out enough to cause that idle shake and that means overhaul time.

If you want to get rid of it, you will have to take the pump to a GOOD diesel injection shop and have that thing overhauled, calibrated and timed correctly.

At this point in time most of the idle shake issues in these cars will require overhauling the pump or at the very least recalibrating and that means taking it off the car.
 

· Registered
1976 450SL, 1992 190e 2.3, 1984 300D turbo, 1966 VW bus
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1,819 Posts
Discussion Starter · #8 ·

· Registered
1984 300D
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5 Posts

· Registered
1976 450SL, 1992 190e 2.3, 1984 300D turbo, 1966 VW bus
Joined
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1,819 Posts
Discussion Starter · #13 ·
Here are compression readings. Verified by multiple different gauges. I tried both glowplug and injector hole. How is this possible at such low mileage? It defies all logic.

Font Number Screenshot Rectangle Parallel


I even tried soaking the cylinders in marvel mystery oil for 4 days and didn't help.
 

· Registered
1984 300D
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5,798 Posts
Here are compression readings. Verified by multiple different gauges. I tried both glowplug and injector hole. How is this possible at such low mileage? It defies all logic.

View attachment 2793055

I even tried soaking the cylinders in marvel mystery oil for 4 days and didn't help.
The uneven compression you are having can cause the idle shake issue.
The transmission mount is also part of the suspension issue concerning shaking.

Areas that effect compression:
Pistons, rings, cylinder walls

Valve seating

Head gasket

Sealing of the prechamer and injector

Cylinder head cracks.

I think that is all of it.
 

· Registered
1984 300D
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5,798 Posts
When I had sticking piston rings on my Volvo diesel, I did the marvel mystery oil soak for a whole 7 day week and rotated the engine did it again with the intentions of another whole 7 day week but only got 3 more days till I needed the car. But it worked. And I was surprised it did.

Others have said running synthetic oil also frees up sticking piston rings, but it takes 200-300 miles of driving.

Concerning the uneven compression and milage who knows what happened during that time. Did a past owner have the water pump leak and the engine overheat to the extent it glazed the cylinders or softened the springy ness of the piston rings?

Did the former owner ever take the Car out on the freeway or was in only run around town?

Valve adjustments are typically not done after warranties are over with. Owner often cannot do it themselves and won't pay to have it done. Some owners don't know the valves need adjustment and even more so as the car is sold to multiple owners.
So valves and seats may not be in good condition or coated with deposits.

Anway that can have an effect on compression.
 

· Registered
1976 450SL, 1992 190e 2.3, 1984 300D turbo, 1966 VW bus
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1,819 Posts
Discussion Starter · #17 ·
My pistons are melted! I removed the pre chambers and used a endoscope camera.

what a load of bullshit, what would cause this?


Liquid Flash photography Fluid Gas Circle


Liquid Flash photography Astronomical object Spiral galaxy Automotive lighting


Atmosphere Sky Astronomical object Galaxy Science


Liquid Water Automotive lighting Fluid Flash photography


Liquid Sky Fluid Flash photography Astronomical object


Spiral galaxy Flash photography Astronomical object Galaxy Circle
 

· Registered
1976 450SL, 1992 190e 2.3, 1984 300D turbo, 1966 VW bus
Joined
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1,819 Posts
Discussion Starter · #20 ·
Gutted. How did this happen then?
It really is a big mystery. This car was pristine with 120k miles when I bought it 10 yrs ago. 20k in dealer maintenance receipts from new, the full package. I take good care of it.

I’ve never messed with the injectors as the car always ran perfectly, never any symptoms.

The injectors I removed had been replaced before, they were bosh India factory rebuilt.

All I can assume is 2 of the injectors failed or my injection timing is off.

these engines will destroy themselves silently. They don’t show symptoms of a problem until it is too late.
 
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