280sl check valve issue

[Travis71280]

Hi all,

I've been having some fuel issues with my 71 280sl lately and i believe its a fuel check valve issue on the return side of the injection pump. The car will run fine, but after ten minutes of driving, the car starts loosing power and eventually stalls out. I check the injection pump and it is hot so i believe it has to be a return line issue. With only the ignition on, fuel barely trickles out the return side of the fuel pump, but when i take the check valve off, fuel gushes out. At what psi is the check valve suppose to open? I tried locating a new check valve online but was unable to do so. Has anyone had any experience in replacing these or retrofitting another type of check valve? Any help is appreciated.

[ja17]

Hello Travis,

You must have the correct pressure and volume from the electric fuel pump in the system first. You can hook a pressure guage somewhere between the electric fuel pump and check valve on the IP.  I use the metal fuel line at the intake cold start valve for the test.

The spec is 0.8 to 1.1 atmosheres pressure in the system before the check valve. Next the volume should be checked.

[Travis71280]

Well, right now i dont have the tools to test the fuel pressure, but I know after I cleaned out the fuel pump I checked the flow and it was flowing about a liter per 15 seconds I believe just before i reinstalled it. It was previously filled with varnish before I cleaned it out.

[ja17]

Hello Travis,

You do not need anything special for the test.  The system is relatively low pressure compared to modern fuel injection systems of today. A standard water or air pressure gauge from a hardware store and some low pressure fuel line along with some clamps will work fine. You can remove the metal fuel line from your intake cold start solenoid and clamp the pressure gauge to it. Try to find a gauge with 60 to 90 psi max so the lower reading will be easy to read.

Most likely your system is ok, but you must rule it out before you can continue looking elsewhere. You may want to leave the gauge hooked up so you can see what the reading is when the engine faulters next time.

[Travis71280]

Thanks ja17, ill let you know when i perform the test on it.

[Travis71280]

Hey ja17, thanks for the advice about checkin the pressure. I'm happy to say I finally got the fuel system sorted out. I was unable to work on the car for tt he past couple months due to college classes goin on, but I was finally able to work on it the past couple of weeks. It started out with my fuel pump leaking. I ended up replacing every O-ring in it (its the new style). The large O-rings were really hard to find because I didn't think it was worth payin $40 for a single oring from the MB dealer. Finally got some from a hydraulic shop and popped them in and now no more leaks. So after I rebuilt the whole fuel pump again, I knew it was producing the right pressure even though I was unable to stop by Ace and get a pressure guage. After examining the check valve I realized the plunger inside it was getting in a bind restricting flow severely, so I took it out, drilled out the check valve so it flowed freely, then went down to Advanced Auto and put a Mr. Gasket pressure regulator right where the T connector is by the gas tank. I'm happy to say the car runs great now and the fuel injector pump is running real cool to the touch even with the water temp running around 200 (i let the car idle a while). Now all I got to do is perform the Pagoda CO test on it since the car still seems to be underpowered slightly and eventually get an electric fan to fix the overheating issue at a long sustained idle which the car always had since my grandpa bought it back in 82.