My 81 300D seems to have air in fuel. (My teenage son may have ran the tank too low and got air in, if that's possible, or may have run out of fuel.) Hard to start. Filled tank and primed over and over and finally started with pushing accelerator down to floor. After driving about 150 miles and tank gauge at about 2/3 full, car started idling poorly, sputtering, especially up hills, and now will not start again, just like before. I have read a lot of posts about finding leaks in the fuel system. But my main question is about the fuel primer hand pump. Mine does not seem to act right. My owner's manual says to rotate the primer handle counterclockwise to activate it, but mine will turn either direction indefinitely and it doesn't seem to make any difference. (The top on my primer pump that I grab to pump it is black plastic.) I'm thinking I'm not doing something right or the primer pump is not working because it never gets any more difficult to push down no matter how long I do it. What does it mean to "activate" the primer pump? Any experience with this or any advice? Thanks.

A primer pump in good shape is used by turning the knob counterclockwise to UNLOCK it. You then pump it up and down to pump fuel. Once pumped, you push it back down and turn clockwise to lock in place.

They are inexpensive and easy to change.

Good luck,

OK, thanks. If the pump is working and no leaks then it should be fairly hard to push down, right?

If your primer pump is black, and can be pushed down, then springs back up, you have the new much improved primer pump (Image below if it works). if you loosen the bleed bolt on the fuel filter housing it should squirt out air and fuel while you pump. Another way to see if the primer pump is functioning is to watch the bubbles in your prefilter, if they move a bit you have fuel moving. If your prefilter is empty then you've got other problems.

__________________
83 240D four bagger stick diesel 276K

To Maxwell: That's what my primer pump looks like. I'lll check it out per your advice. Thanks.

The newer pump, like you have, is easy to pump.... hard to tell that you're doing anything when you pump it. You don't have to turn it to "activate" it either.

__________________
1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k

To Wasuchi: OK, that's good to know about the primer. I used the primer last night while opening the bleed valve on the main fuel filter, as Maxwell suggested. I replaced the rubber fuel hose from filter to #1 injector as it was leaking badly. That was definitely a big problem, if not the only problem. Finally got engine started after several cycles of turning ignition with accelerator floored and then getting out and pumping primer. So far so good today. Thanks for info and advice. I learn a little more about this great old car with every problem!

I have the same primer pump, so how does it work? Do I suppose to just push down on it without turning? Do I need to pump it? Thanks...

300cd,

You only need to pump it when you change the filters or do something else to introduce air into the fuel system. All you should have to do is press it down and it should pop right back up, I think I've seen to pump it between 20 and 50 times (until you get fuel in the filter)..... I've never had to pump more than 10 or 15 times.

__________________
1985 300D Turbo ~225k
2000 F350 (Powerstroke) 4X4, SWB, CC, SRW, 6spd ~148k
1999 International 4900, DT466e (250hp/660 ft/lbs), Allison MD3060 ~73k