280sl injection pump 1970

[Markbrock]

I have a new reconditioned injection pump with fuel going into the pump but not returning causing fuse too blow and fuel pump too my a horrible noise.both fuel line hoses and tank and fuel pump are new.im thinking maybe shut off b
Valve on back of injection pump is holding the fuel in pump.....can anyone help on this subject......great site by the way....

[jeffc280sl]

Hi Mark,

what fuse is blowing?

if you think the shut off valve is the problem i suggest you remove and tape up the power wire to the solenoid.   its part of an early emissions control system in late model 280sl's that shuts off fuel when coasting to reduce unspent fuel in the exhaust.

[behnamlaw]

does you Mechanical Injection Pump MIP have 1 or 2 rear solenoids? Disconnect both and try again

[Shvegel]

Shut off solenoid doesn't turn off fuel recirculation. guaranteed.  there are 2 fuel hoses on the pump the aft one is the return.  I have a feeling the check valve at the return fitting is probably stuck. Remove the return line from the fuel damper then put the end in a bucket. Turn the key on and see if you have fuel there?  If not remove the fitting where the line exits the FI pump and gently push the valve open from the pump side to the hose side.  A piece of wood like a chopstick would be ideal.

[Markbrock]

Do you mean the valve on the pump.just too add both return line are all ok on the damper side all new.there is no fuel coming out of the return valve at the pump return.so are you say that must be stuck.....thank you for your reply’s this is a problem i have not come up against before,

[Shvegel]

Not sure if this is possible but are the inlet and outlet fittings swapped?  The front fitting should be wide open and the rear fitting should have a brown or white plastic check valve in it.  If they are not swapped the rear fitting might be stuck.  Basically the primary fuel system.(Electric pump, filter, damper and lines exists to just keep the fuel chamber on the Injection pump filled.  Pressure into the pump that over pressures the outlet fitting then the fuel returns to the tank.   If there is no demand for fuel then it just flows through the fuel chamber and out the back of the pump.