280SE fuel injection pump overhaul

[jbiordga]

After letting my '69 280SE cab sit up for over a year (I know, bad, bad) it will not run. The fuel injection pump is only delivering a bit of fuel from #4 and #5 spigots. I've verified the fuel supply pump is delivering an adequate volume and we got the car to sputter by jumping the cold start solenoid. A few years ago I had the fuel injection pump overhauled by a gentleman in the Northeast somewhere. He was recommended as some as good as Gus at Pacific. Anyway, can anyone recommend a course of action I might take or can anyone supply me with the possible name of the guy who did the overhaul (I know there are just a few of them left out there) so that I can go back to him on it?

[ja17]

Hello,

You have stuck plungers in the injection pump. It is more commonly known as a "stuck rack". In actuallity most often the plungers are stuck causing the rack not to move. This is caused by long periods of inactivity (storage). Varnish from dried out fuel and rust from moisture in the fuel will cause the plungers to stick over time. At times these plungers can be freed with the pump still on the car. The lines on the injection pump are removed, the 19mm fittings and the check valves below are removed and the exposed plungers and cylinders in the injection pump can be doused with penetrant, exercised and freed. When re-installing the check valves and fittings, the fittings must be torqued to 18 ft/lbs.

[kmukherjee]

There is an inspection plate you can remove to access the rack. Give Hans Utke a call from H&R Fuel Injection in Bohemia, NY. He is the person you were referring to. Very knowledgeable and capable.

[tinypanzer]

Hans Utke in Bohemia, NY. Now THAT is a proper name and location for an MB mechanic!!

-tp

[Arthur Dalton]

To add to JA post on exercising the rack as the penetrant cleanses .
....there is a Rack access port with a 10mm plug in the front of the pump. Take that cap off and you can thread a 4 x .8mm machine screw [ about 2" long] into the threaded end of the rack..this is actually a test bolt used for tuning , but we also use it with stuck racks to slide the rack foward/back as the penetrant does it's job...don't force it, just use it to help the freeing process. When you can finally move this test bolt freely , you know the rack is free...if you pull or push the rack , when you let go of the screw , the rack will return to self center itself. That is when you are sure all is free. You can also use a standard 10-32 screw in place of the the metric test bolt b/c the threads and diameter of the two are that close in spec and interchangeable.......

[Chas H]

Originally Posted by tinypanzer

Hans Utke in Bohemia, NY. Now THAT is a proper name and location for an MB mechanic!!

-tp

Tha last time I sent a set of diesel injectors to Hans, he lied to me about shipping them back. When I finally got them with a COD for $85, they had only been wire brushed and not re-built. He charged me exactly what they were worth as cores for re-building.

[tram]

Originally Posted by Arthur Dalton

To add to JA post on exercising the rack as the penetrant cleanses .
....there is a Rack access port with a 10mm plug in the front of the pump. Take that cap off and you can thread a 4 x .8mm machine screw [ about 2" long] into the threaded end of the rack..this is actually a test bolt used for tuning , but we also use it with stuck racks to slide the rack foward/back as the penetrant does it's job...don't force it, just use it to help the freeing process. When you can finally move this test bolt freely , you know the rack is free...if you pull or push the rack , when you let go of the screw , the rack will return to self center itself. That is when you are sure all is free. You can also use a standard 10-32 screw in place of the the metric test bolt b/c the threads and diameter of the two are that close in spec and interchangeable.......

I'm battling a 230SL that has sat since 2000. I have fuel pressure to the IP, but none out of it.

How much movement should the rack have with the machine screw? This one pulls forward and springs back- but only by what seems to be less than a millimeter. If I recall, it should be about 13mm or so. Of course, no spec in the book.

I'm thinking that I need to pull the top of the pump apart and free up plungers. I'll probably soak the injectors also. Right track?

[ja17]

Yes the rack will normally move more than yours. You should be able to push and pull on it and make it move. Stuck plungers (pistons), cause the rack to be stuck in most cases. If you remove the fittings on the IP and remove the check valves, you will be able to see the top of th IP pistons moving up and down as you rotate the engine. If any pistons fail to move downward, they are stuck. Use penetrant for rust, alcohol works best to desolve fuel varnish. Try both. Keep working on them util they all move up and down on their own as the engine is turned. When this happens the rack will normally be free.

The injection pump fittings MUST be re-torqued back in place at 18 ft. lb psi. The latter pumps a bit more. Too little torque and you will get no fuel. Too much torque can damage the pump.

[tram]

Thanks!

[tram]

OK, back to square one. I wound up having to take the IP off and as far apart as I dare. I soaked it first in alcohol, then penetrant, then diesel fuel. I got all of the plungers freed up nicely and everything cleaned and flushed out now.

BUT- the rack still doesn't move more than 2 or 3 mm. Barely at all. Everything seems freed up other than that, and I release the rack and it "clicks" back. The plunger pieces that the rack moves all move freely, but just perceptibly with the bolt in the rack.

Does ANYONE know about how much this rack should move? I'm fairly sure this just isn't right, but I can't find a spec.

Thanks in advance for any help/ info/ insight.

[ja17]

Hello,

Some racks have a threaded hole in its front end. You can thread a screw into it through the front access and the rack should be able to move in and out about an inch if you push and pull on it.

If you use only the accelerator linkage to move the rack, it will move only a few mm . The centrifical governor inside the pump actually moves the rack the most when the engine is running at different rpms.

[tram]

Originally Posted by ja17

Hello,

Some racks have a threaded hole in its front end. You can thread a screw into it through the front access and the rack should be able to move in and out about an inch if you push and pull on it.

If you use only the accelerator linkage to move the rack, it will move only a few mm . The centrifical governor inside the pump actually moves the rack the most when the engine is running at different rpms.

Yep, I have the pump out and the cover plates off, and the bolt threaded into the hole under the plug at the front of the pump. Nowhere near that amount of movement... Like I said, MAYBE 3mm.

Electric starting valve is off and not frozen. All the plungers move. the camshaft spins fine. But the rack barely moves, and it feels like a hard mechanical part limiting the movement.

Any ideas?

[tram]

Update: Got it. Wound up having to tap the bolt side in, then tap the rod back the other way from inside the back with a light brass punch and a light hammer.

Couple more hours cleaning, moving the rack, soaking, and oiling and I got the rack to move about 25mm both ways, and snap back to center, as it should be.

Everything in the IP seems to be in order now. We'll see what happens when I put all the cover plates back on and put it in.