So I've got a vague problem I'm hoping for help with.

I have a 1984 Mercedes 300TD wagon with ~250k miles that runs really well and is overall in good shape. I change my fluids regularly and take care of it, but problems are inevitable.

When the car is cold, it starts every time with no problem. However, if I turn the car off and want to turn it back on with 15 minutes or so, it cranks but won't start. I usually have to crank about 4 times, waiting about 5-10 seconds between cranks, and then it'll catch. If I'm starting and stopping a lot, the engine sometimes loses power and I have to repeat the process.

Money's tight, and I don't mind getting my hands dirty, but do you have any advice as far as where to start troubleshooting this problem?

Thanks for the help.

From your description it's pretty obvious your starter is working fine, so it's not a starter problem.

Diesels need compression and fuel within a tight timing range to run. Since you provide no other data, I'd begin by assessing the basic system data. In no particular order

- Do a compression test
- Check for air leaks
- Do a diesel purge
- Check your fuel spring length
- Adjust your valves
- Replace your fuel filters
- Clean your fuel strainer
- Replace the timing chain, if not already done
- Pop test your injectors
- Check your lift pump

If everything checks out and the problem persists it might be something with the IP or timing.

My best guess is that it's air getting into the system....

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Current Stable

• 380SL (diesel)
• Corvette C5
• Manx
• Baja Bug
• F350 Powerstroke
• Auburn Boattail Speedster replica

Put a temporary clear 1/4" i.d. 3/8 o.d. PVC tubing in place of the return to tank line (aka cigar hose). Chances are you will see air with engine running and engine off. Find and fix the air intrusion and that will likely fix your starting problem. That is the cheapest and easiest thing to try first. Report back what you find.

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85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

On your engine, the most notorious part that introduces air into the fuel system is the white primer pump. It is the type that you have to unscrew and pump several times to prime the fuel system. If you still have this older type primer, there is a new style replacement that resolves this issue.

1984 Mercedes-Benz 300SD Base Sedan - Fuel System - Page 3

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Sam

84 300SD 350K+ miles ( Blue Belle )

After you duplicate the no start situation disconnect the vacuum line from the Vacuum Shutoff on the fuel injection Pump and see if it will start. If it does it is likely the other Vacuum Shutoff Switch that is on the Steering Colum Lock.

Or as previously said the valve need adjusting.

Try starting with the Fuel Tank Fill Cap off. If it starts it is likely your Fuel Tank Vent is obstructed.

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84 300D, 82 Volvo 244Gl Diesel

So it's been a while, but I figured I'd follow up. I brought the car in to a mechanic for some other issues and he went ahead and took care of the ignition problem too. The problem was with my vacuum system. He rerouted and plugged some hoses and I haven't had a problem since. Thanks for all of your help.

Thanks for the follow up.

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84 300D, 82 Volvo 244Gl Diesel