replacing manual primer pump - Mercedes-Benz Forum
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#1 (permalink) Old 09-20-2010, 11:09 AM
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replacing manual primer pump

so, ever since i replaced my fuel filters a week ago, i have not been able to get my 1985 300d started again. i have searched and read all applicable threads, but am having no luck.

i believe my problem is due to two things:
1) the car is parked on an incline (headed uphill). i think the fuel pump lacks the oomph to bring fuel from the tank up to the pump. the fuel pump worked fine before i replaced my filters. i don't wanna roll the car off my lot, not be able to get it started, and have it sitting in the middle of my alley! i have bled and cranked, and bled and cranked for hours now...

2) my primer pump is shot, and i cannot loosen it to replace it. i have a good pump on my parts car, but can't get either one off, as there is little room to get tools in there, and the nipple for the fuel supply line blocks the head of a wrench. how are these removed?!?!

i blew some compressed air into the tank, and i got fuel at the inline filter right away, so i know the tank screen isnt blocked. i have cracked the lines at the injectors and got fuel at each one, but no start! i think that the primer pump is the last component i need to prime the system and get her started again. what can i do?!

thanks guys. obviously i am out of ideas/resources here!
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#2 (permalink) Old 09-20-2010, 12:16 PM
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1) probably not a fuel pump issue

2) Vice-grips. You'll need to remove the fuel line up stream for more access if you haven't done so already. You will ruin the primer pump so will need to replace with a brand new unit ($30).

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#3 (permalink) Old 09-20-2010, 12:42 PM
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^ Agreed, I use vice grips, it's on there, so use some force.

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'84 CD-weekender!
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#4 (permalink) Old 09-20-2010, 01:03 PM
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If you feel there is no room for a Vice Grips and you have one you can use a plumbers Basin Wrench (but only for removal). Do a image.google.com search to see some pics.

Getting a the new Hand Primer back on is easier done with the right sized Crow Foot Wrench on an Extension.

You also have option of removing the complete Fuel Supply Pump. There are 3 each 10 or 12mm nuts holding it onto the Fuel Injectin Pump.

After you are done pumping on the Hand Primer loosen the Fuel Injection Tubing/Lines at the Injectors. Crank the Engine until you see a resonable amount of Fuel coming out.
This bleeds the Air out from between the Fuel Injection Pump and the Injectors; where if it gets trapped is hard to get out due to the Air compressing a lot and moving only a little.
Loosening the Fuel Injection Line Nuts at the Injectors allows the Air to easily escape.

Last edited by 300Dman; 09-20-2010 at 01:08 PM.
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#5 (permalink) Old 09-20-2010, 02:18 PM
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The new style has a more reasonable 17mm hex on the bottom, I use a stubby open end. But have installed one with a regular length open end.

I've found simply replacing the primer pump, pump it, start the car, no need to bleed each injector.

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#6 (permalink) Old 09-20-2010, 02:27 PM
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thanks for all of your help, yall. i have bled the injectors, they get fuel. i have bled the banjo bolt on top of the fuel filter, and the bolt that tightens the fuel filter. i have to think that my primer pump is letting some air in, even though it's screwed in tight.

new primer pump ordered from AZ. hope this is the last holdout!
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#7 (permalink) Old 09-20-2010, 03:21 PM
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Quote:
Originally Posted by johnnyqnola View Post
thanks for all of your help, yall. i have bled the injectors, they get fuel. i have bled the banjo bolt on top of the fuel filter, and the bolt that tightens the fuel filter. i have to think that my primer pump is letting some air in, even though it's screwed in tight.

new primer pump ordered from AZ. hope this is the last holdout!
I just bought a heavy duty Monark primer pump for the 240D. BUT, I couldn't get the old primer pump off even with vice-grips and lots of pen oil. Thankfully, it still works, but I'm keeping the new primer pump handy for the next time. Not if, but when...

2005 230 K, 26k-77k (sold)
1982 300 TD, 167k-226k
1982 240 D, 308k-327k (sold)
1998 E 320, 120K-141K
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#8 (permalink) Old 09-20-2010, 03:59 PM
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I removed the entire lift pump for installation of the new hand pump. Makes it quite easy.



Watch out for oil coming from the diesel pump and don't forget a new gasket for installing the lift pump.
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#9 (permalink) Old 09-20-2010, 05:22 PM
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I have found that a 15/16" wrench (cheap) bent at a 90 degree angle about an inch from the open end will take that old primer pump right off, without disconecting or moving anything. tighten the new updated pump with a crow-foot extension or a stubby wrench.
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#10 (permalink) Old 09-20-2010, 06:35 PM
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The primer pump can scavenge air into the system if it's leaking. Fuel getting out = air getting in. If the old style mushroom-looking thing is in place, it probably needs replaced anyway. Once they get froze up, it's shot. Good news, brutalizing the old one gets it removed. Pulling the banjo line gives enouigh room. The new one should look like the one in the phot o(thanx, Govert), and go on with a 17 mm crowfoot. Stinky job, but necessary.
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