108 info here helpful

[showbizfcb]

This is my first posting here. I have been searching the archives for several weeks now trying to get my 72 280SE 6 cyl to run. I've done everything I could fine here. Fuel doesn't come out of the injection pump. The last thing I did was pull the side off of it, clean it with carb cleaner, and work the plungers manually up and down. It still doesn't run. It ran in the fall when I parked it. I have listed it for sale here before it goes to ebay.

Thanks for the help. This is a really cool site.

fcb

showbizfcb@hotmail.com

[wbain5280]

Does the fuel pump run? It's a low pressure electric one by the fuel tank.

Yes, the fuel pump by the tank, which can get stuck with gummy varnish from evaporated fuel. It's a low pressure and high volume pump. Sometimes you can very carefully take it apart and clean it out. First, I would put guage on the mfi pump and see if you get around 12-15 psi there.

I had the same thing happen to me once on the 220SE, I felt really stupid when I realized it was out of fuel even though the guage showed half a tank.

I think Carson356 knows quite a bit about the mfi, hopefully he can chime in.

[showbizfcb]

I've had the rear fuel pump apart a couple of times. Replaced the brushes in it and it jumped right to life. Not sure about the psi. I'm assuming it's in spec. If I don't tighten everything up it squirts gas everywhere. Since I'm selling the car I don't really want to buy a new one. As everyone knows, they're kinda pricey.

When I take the return or outlet from the injection pump off it squirts gas under pressure. I know I'm getting gas to the injection pump. I am getting spark on each plug. When I take off the metal lines coming out of the injection pump there is no gas.

If I spray a little bit of ether at the front of the air cleaner it starts to run. I have not filled the air cleaner up with ether though. Just enough to tell that if it had fuel it would run.

Thank you for your ideas. I'm real close.

fcb

The rack inside the pump might be stuck, and not allowing fuel to get to the delivery valves(plungers). IMHO, it's doubtfull all six plungers are stuck. I wish I knew how to tell you check the rack, though I think it invloves using a bolt screwd into the rack after reming a access plug. Surley, someone here knows how to do this? Anyone? Bueller???

[wbain5280]

There is a fine mesh steel fuel filter under the injection pump on the engine support arm. It may be blocked. There are also two fuel dampers, round things with fuel lines going to them, that smooth the fuel flow. They also need to be checked.

[showbizfcb]

Thanks for the help guys.

On the rack. I'm not really sure what it is. I bought a couple different sizes of M5 screws. I have a real MB blue manual that cost about $80. It said that there are two kinds of pumps. One with the screw to check the rack and one with out. I think I have the one with out the threads. At the front of the pump there was a black plastic cap that I pulled off. I think the rack is suppose to inside the end of this piece. I could not get it to move or turn in anyway. Am I in the right place?

I can check the screen under the pump. Not sure about that one. It's worth the try. The round unit you are talking about, it is outside the pump and bolted to the frame? It's got fitted hoses with metal ends in and out of it. If it's what I'm thinking about gas does flow through it.

Open to suggestions. Thank you.

fcb

I'm pretty sure the rack is behind the cover you removed. I think the rack has female threads you can srew the bolt into.

I stole this off the internet I hope it helps:
"......does the control rack move freely? Remove the plastic plug and the driven end of the pump, insert the blunt end of a biro and gently push into the pump and release pressure. The biro should move back to the original position. If not, a gummed up pump is what you have."

also:

"Pump seizure — MFI pumps which have been allowed to stand idle for long periods with oil and fuel in side them often suffer from binding or sticking control racks and gumming up of fuel galleries, as well as possible seizing of internal components of the pump and regulator. To overhaul such pumps, fill fuel inlet with carburetor cleaner (or methyl alcohol), Remove plastic plug above driving cog (back of pump housing) and insert the blunt end of a plastic biro or similar non-metallic object into the hole to contact the control rack. Using slight pressure, gently push against the control rack while turning the drive cog clockwise. This is best done if the MFI pump is clamped to a work bench. Push and release the biro as you rotate the cog. Repeat this procedure until the rack moves freely with the MFI camshaft using very little pressure on the biro. You may have to add more cleaning fluid and repeat the steps several times. If, after several attempts, the control rack is still stuck, it is time to send the pump off for a rebuild"

[showbizfcb]

John- Thanks for the advice. I'm guessing a biro is some kind of stick. Sounds like I just want to push on the end of the rack with something softer than a screw driver.

The manual I have sez that some pumps are threaded and some are not. I have one that is not threaded.

Thank you for your help. I try it later this week.

fcb

[Arthur Dalton]

Your pump is R24 , so no threads for test screw on rack.
[pre R22 have threaded racks]

Take line fitting off at Cold Start Valve on right side of intake. Hook rubber fuel hose to line and place end in container and turn on key.. you are looking for 1 litre flow in approx 15 secs.
If so, put line back on CSV and run a jumper wire from bat + to the CSV while energizing the starter. Car should start and continue to run from CSV fuel long enough for Injection pump to bleed itself and injector lines. When that happens , you remove jumper to CSV... basically the same as hand choking an old carb engine that has sat around for a while..
Give it a try and report back what you find.

Ah yes, I forgot about that old trick. I once saw a 250SE brought back life in that fashion. I wish my old 220SE has a csv. Though someone wired a toggle switch under the dash to pull the rack into a "choke" position to help with vapor lock. It has a early ZEA pump.