How would you start this car that sat 20 years?

[Fonzi]

2.5 m129 250se.  The clutch didn't pop back out when we pushed it to the floor.  So it's not like we are going to be cruising this thing around tomorrow.  I know I should drain the tank and get fresh fuel up to the engine bay.  But what do I do about the injection pump and fuel injectors?  Does anyone have a procedure they like to follow for "barn finds"? 

This car was well cared for and has fresh looking oil, and even still has some residue of oil on the cam lobes visible from the filler in the valve cover.  All was polished and cleaned, and I'm still in contact with the seller that says he last started/cranked it in the mid nineties, about 20 years ago. 

Thoughts?

Thank you!!

[scoot]

Go through the Kent Bergma "bringing the 6.3 back to life" video series.  Basically exactly the same thing.  Took me a long time on my M189 engine.

[Shvegel]

The first thing to not do is to put a battery in it and turn the key. The electric fuel pump may very well be frozen with varnish and if it fries it will cost you $1600 for a new one.  Having resuscitated a car that sat for 20 years I can tell you the fuel system will be your biggest most expensive roadblock provided the engine turns.  If I had to do it again I would source a new fuel tank and lines and start from scratch.  Even if you are able to get it running with the parts you have any microscopic rust particles will tear up on your injection pump and cold start injector. 

Step by step:
Verify that the engine turns by turning it by hand at the big nut on the crank.

Change engine fluids

Replace tank and lines

connect battery, disconnect ignition coil positive wire

Turn key on and listen for the electric fuel pump.  If you don't hear it turn the key immediately off and have the electric pump rebuilt. I don't suggest you try opening the pump yourself because the screws on the cover tend to corrode and can be impossible to get out.  Much better to have it done by someone who has been down that road before unless your idea of fun is drilling and tapping out tiny little steel screws in very expensive aluminum.
loosen the fuel lines at the injection pump being careful not to loosen the fitting on top of the injection pump. and verify the each one is squirting a little fuel when the engine cranks.  When you loosen and re-tighten the lines I would strongly suggest holding the fittings on the top of the pump to keep them from turning.  If you loosen them when removing the lines you run the risk of creating an internal fuel leak in your injection pump and if you overtighten them you can strip the fittings out of the aluminum housing.  As a workaround there is a Carter fuel pump that will take the place of the Mercedes / Bosch one for a fraction of the cost (Search this site for Carter fuel pump).

If all that checks out re-connect the coil and give it a try.  If it starts and runs perfectly great. Let it run for 15 minutes or so.  Change the oil again and do a full tuneup including ignition points, valve adjustment etc.  Don't throw spark plug wires at it "Just because"  the original wires seem to work fine even after years of sitting and most of the aftermarket wires are junk.

Change coolant again after a few hours of running.

It all sounds easy enough but there are a number of things in there that can be challenging to repair the biggest being the injection pump.  If you do not get fuel from all the fittings on to top of the injection pump it usually means that one or more of the pistons in the pump are stuck up with varnish. Joe Alexander has explained how to fix this a few times on the forum so I suggest a search of the site.

 

[Benz Dr.]

Forget about the fuel pump and pull fuse number 4.  Remove the spark plugs and spin engine until you get oil pressure.