Pressure Check Valves / 280SL

[mtoomey]

Anybody have any around?  Mercedes 000 074 1715, Bosch 417 412 001.

Let me know, and thank you!

[Fonzi]

I just today tried to clean the number 4 cyl check valve in my 1969 280se injector pump and failed.  It doesn’t hold pressure either way it seems.  When the pump turns on, the fuel flows out of this cylinder only.  Then when the injector is on, it does not flow.  Now that I see that these are over $250 at ECS Tuning, the only place I’ve found one, and not even sure they really have them.  I’m not sure my IP is even any good.  This is a parts car I was trying to make run before tearing it apart.  The IP and check valve is different than that in my 1967 250se.

[mtoomey]

Still looking for these!

[Pawel66]

Found them on ebay a year or so ago. $100 a piece already at that time...

[Fonzi]

Is there a testing method for the check valves?  My belief if that one of mine is bad in my r20y IP because the pump will flow fuel when no injector is attached but won’t flow with an injector.  The only test I can think of is to swap the check valve with another cylinder. 

[Pawel66]

There is.
1. Undo the fuel lines.
2. Push rack in.
3. Switch on the ignition (fuel pump)
Fuel coming out - bad valve, not coming out - good valve.

This is from BBB, I hope I did not mess up anything... may want to check...

[Fonzi]

Thanks for that.  I didn’t know they weren’t supposed to flow in either direction.  I thought they were just supposed to stop backwards flow, allowing pressure to build in the fuel lines while pressure on the pump side might decrease. Interesting that they should prevent forward flow at low pressures too. 

On the “push rack in” part, should this be done with the rack motion thing under the black cap, or can we just do it with the throttle linkage?

[Pawel66]

I think they open in "from the pump out" direction at higher pressure, when FIP is working. If the white seals are leaking, you will see it too.

Push the rack from the front of the pump, from the side of the black cap.

I can get you exact wording from BBB on Friday, when I am home. Hope I did not mixed up anything.

[Pawel66]

I checked with BBB. The steps I omitted were:
1. Clean the pressure fuel lines at FIP before unscrewing.
2. Blow the connectors after unscrewing the fuel lines with compressed air - I understand to get rid of potential dirt that might have dropped into the connectors during unscrewing and to blow out remains of fuel that may be there so that you can see fuel level raising inside the connectors in case the check valve is faulty.

Maybe also: push the rack to "stop".

The rest is as I stated before.