Sticking Pressure Valve? In Injection Pump

[vp1122]

Hey guys, I have a 1967 250 SL, I have just finished a restoration on the car. The engine has not been rebuilt, here is my issue. I have no fuel going to my number 1 cylinder. I pulled the line off at the pump and still no fuel. After pulling the side cover off of the pump, (the pressure valve? the spring mechanism with a collar at the top and a sleeve at the bottom)(sorry I am new to the old Mercs!) for number 1 seems to be being raised by the internal cam but will not return down, I can push the sleeve down with a little screw driver, but it will not return by itself. The rest of the units function as they should. I assumed, since the engine sat for 3 years that there was gunk and varnish built up. After soaking in cleaner and then with diesel fuel the sleeve will still not return on its own. My question is, could it be more complicated then just varnish and gunk? is there another return type coil spring I am overlooking? Has anyone encountered this problem before? Thanks so much for your help.

[ted280sl]

On the East Coast we have Hans at H&R Fuel injection, (631) 589-1600. He really knows these pumps and he is a friend of the group. I would suggest contacting him before going any further. There is also someone on the west coast but, I do not know who it is.
Good luck,
Ted 1969 280SL
PS: I visited Hans. He is a former Bosch employee. He has some very expensive looking equipment which he uses to rebuild Bosch pumps.

[glennard]

vp, Is the rack(rotates all pistons) jambed someway on 1?  Each piston has a coil(pretty strong) spring.  Is it jambed on 1?  Pistons/cylinders are very close tolerances.  Doesn't take much crud to hang them up.  PB Blaster and a lot of rotations and cam turns!

[vp1122]

Hey Glennard, good point, and another question, I did put a bolt in the end of the rack, and it moves slightly 16th of an inch or so, how much movement should the rack have? The piston is driven up from the bottom? it looks like there is a cam type unit that moves the springs up and down with the timing of the engine, correct?

[glennard]

vp, The knee bone is connected to the.... The pump cam shaft is driven in sync with crank/valves and drives the pump pistons up.  Springs drive them down.  Pistons have helical groove on them.  As the rack rotates the pistons, more or less helix is exposed to vary the fuel volume.  The rack teeth do the rotation from the throttle/etc. demand.  As I remember9?) the rack moves about 3/4 inch and rotates the pistons 120 or so degrees.  M5(?) bolt in the end of the rack should move it freely with no resistance.  Sounds like your's is still gummed up.

[ja17]

Hello Vp,

If one piston is stuck the entire rack will bind.  Your numper one piston (plunger) in the injection pump is stuck. Remove the injection line remove the 19mm fitting on the pump which is over the stuck plunger. Below it you will find a check valve. The outer circumference is threaded so you can screw a fitting on it and pull it straight out. Below it you will be able to view the plunger and the cylinder. Soak the assembly with your favorite penetrant. Rotate the engine and verify that the plunger does not return. You can take a wooden golf tee and tap the plunger downward to make it return. Exercise the rack and the plunger by turning the engine and tapping the plunger down. You should be able to free things up.  When the plunger is free, the rack will also free at the same time. Not a big deal, I have unstuck many of these.
It is critical to re-torque the 19mm fitting to 18 ft. lbs. during re-assembly. I will post some photos shortly. Keep us up to date.

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Joe Alexander
Blacklick, Ohio

[glennard]

vp, From memory- with cover plate off and assembly in PB Blaster/Mystery Oil, gently wiggle the rack while rotating the cam shaft.  You don't want to jump a tooth or loosen the piston clamps(rotate the helix).   Helping the spring return the piston each stroke is probably needed until it frees up.  Each stroke of the piston delivers only a few hundred of a milliliter of gasoline to the spray nozzle in the cylinder head.

[vp1122]

Hey guys, so I got the plunger free and moving well. Now it won't start, I have fuel at the lines at the pump, and just a little at the injector.. Spark is good. Do I need to bleed the lines? or is there some way to re pressureise the system?

[ja17]

Hello,

You might try jumping a hot wire to the intake starting valve while someone else is cranking the engine. A few seconds should tell  you what you want to know. Do not connect too long or you will flood the engine.


Joe Alexander
Blacklick, Ohio

[vp1122]

She is going strong, purring like a kitten, Thanks guys so much, I really appreciate the help.

[hands_aus]

quote:Originally posted by vp1122

She is going strong, purring like a kitten, Thanks guys so much, I really appreciate the help.

Yeah, but what did you do to get it going, finally?

Bob Smith (Brisbane,Australia)
RHD,1967 early 250 SL, auto