I am new to the forum, Mercedes and diesel. I just got a 1980 MB 300SD turbo diesel with 95000 original miles. It runs fine on the road, its getting it started that has me stumped. I have to pump the pedal and sometimes floor it just to get it started and idling. I can let it run for 10 minutes, then shut it off and try to start it again and have to floor it. It has been in storage for a couple years and has new fuel put in. What should I look for? Also, did these models come with a second fuel tank in the trunk with a transfer switch on the dash or is this custom made? Thanks

 

From what I was told by the guy I got it from was that he was the second owner. The first owner bought it new and babied it until his passing when he willed it to his granddaughter. She wanted something more sporty so the second owner bought it from her in 2008 and has been stored until a few months ago. No one actually knows why the second tank was put in, but speculation was that he drove from Oregon to Arizona a few times and wanted to drive longer between fuel ups. Could be B.S also! So I might have fuel vapor leaks somewhere and that is what is causing the hard starting? Not injectors or glow plugs? Thanks

 

Back in the day there were a lot of extra tanks installed in vehicles for just that reason, also to be able to buy where it was cheaper, and last 'till it was cheaper again. You don't know that it had "alternative fuels" run in it. Check your glow plugs that is the common cause of hard starting.
Look to see if it has any extra filters, heat exchangers, or extra solenoid valves in the fuel system, that is a telltale of ''alternative" fuels. Don't spend a lot of money on it, but don't just give up on it either, until it becomes apparent that is has internal problems.

 

Diesel does not Vapor Lock like Gasoline does. I think the only way that could happen is if someone ran the Fuel Supply Tubing up against something hot like an Exhaust Manifold or Tail Pump.

You did not say if you were seeing any particles in the Clear Plastic Fuel Inlet Filter?

Is the idle speed set fast enough? On one of the Emission Stickers it has that and the timing information.

If only for test purposes I would disconnect the 2nd tank and return everything to the Stock configuration.

You could get a length of 5/16" Fuel Hose and a Container of clean Diesel Fuel and run that Hose from the Fuel Inlet filter to the Container of Diesel Fuel. Pump on the Hand Primer till you hear a squishing of buzzing sound coming from the Fuel Injection Pump and then pump some more.
If the Hand Primer Pump leaks replace it with a Bosch New style one. The old Style Hand Primer with the Hard Plastic **** and shiny Aluminum body are a noted cause of Air Leaks.

If the Hand Primer is good and the Car will start like that and start again OK after you wait I would suspect you have a Fuel Supply problem.
That could be the Fuel Supply/Lift Pump (it can be rebuilt) that the Hand Primer screws into or the Fuel Pressure Relief/Overflow Valve is not holding pressure at idle.

Doing a Valve Adjustment also helps starting.
Are you using the Glow Plugs before you Start? Have you checked the Glow Plugs to see if they are all working?

 

17 mm socket or wrench. couple rags and some rubber gloves. Loosen the injection pump manual pump ****. 4 - 5 full turns to the left. then pull up on the ****, now crack the 17 mm bolt on top of the filter housing. 1/2 turn approx. Now pump the manual pump **** / handle while looking at the 17 mm bolt for signs of air bubbles. Keep pumping until there are no bubbles. Now tighten the 17 mm bolt and then tighten the pump ****, again 4 - 5 turns to the right. This will help you determine if there was air in the system which was causing rough idling.

 

Diesel surge cleared my hard start symptoms... Any air bubbles in the clear filter under the hood??? If you search diesel surge I'm sure there is a tutorial of sorts... It's part of Maintainance now... And kinda fun to watch!!! Kids love it!!!

 

Are you sure you did not mean; Diesel Purge?