Fuel Pump Check Valve

[glcg123]

MY 1965 230 SL is hard starting when cold. The CSV appears to be functioning correctly. I don't think it is getting enough fuel at the beginning when it has been sitting overnight. A mechanic suggests that the check valve just at the feed line from the pump by the tank could be allowing fuel to evacuate the lines causing the condition and the long crank time. Has anyone had this issue? The valve from MB is $92 but I likely will have to run the tank down to change it out. Ideas?

George

[Jordan]

George, if you are talking about the one on the electric fuel pump at the back end you can just clamp off the fuel lines going into and out of the pump, remove the lines from the pump, remove the pump and check the valve.  You don't need to run the tank down.  I use cardboard between the clamp and rubber fuel lines so they don't cut into the rubber.  I've done this several times so i could remove the pump to work on it.

[twistedtree]

It would also be pretty easy to tell if this is happening.  When you turn on the ignition, the fuel pump will start running.  Just listen to it, and in particular listen to how long it takes for its sound to stabilize.  When it's pumping but not making pressure you will get one sound, then once the lines are full and pressurized, it will make a different sounds and it will stabilize and stay that way.  If it takes a few seconds for the sound to stabilize then you've got leak down somewhere.  If it becomes steady within a second or so then there isn't any leak down.  You will obviously need to let the car sit long enough for any leak down to occur before running this test, but it's pretty simple.

[glcg123]

Thanks to you both for your insight and help. I left it sit for about 5 hours and it took a few seconds for the sound to stabilize so it is the check valve. Once the sound stabilized it fired right up.  Does anyone have a Bosch cross reference number to MB part # 000 091 0710? It's $92.50 at the dealer and I have seen them online for around $20.00. However, I have an original tall pump so it is tough to know the correct number. Ideas? I don't mind paying for proprietary parts but this is a little pricey.

George

[Naj ✝︎]

Bosch 1 446 412 010

Naj

[George Des]

The check valve is a simple device built into the output fitting. It is the same on both new and old style pumps. You may be able to get yours to work by removing the fitting and spraying some solvent like WD 1 into it and working the rubber diaphragm back and forth with a match stick. Once it looks like it is working correctly blow into the fitting first from one side then the other. Air should only flow in  one direction if it fails this, get another from a donor pump. $92 for this is highway robbery.

George

[glcg123]

Thanks for the P/N reference. I will attempt to free it up first.

George

[glcg123]

Well, I finally had my mechanic change the check valve on the fuel pump near the tank. I played with it a few times and was able to get the valve to bypass on occasion. It was the source of the hard start. With the new check valve my car starts perfectly within a couple of seconds. While the new valve was pricey $92.50 my mechanic only charged $37.50 to replace it. It will save the starter motor.