I'm looking to replace the lift pump on my 300SD and I don't have a wrench that will fit it. Are there any o-rings or seals for me to replace? Can I pull one off of a 240D? Thanks

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'81 300SD

The primer pump?

The primer pump(17mm) screws into the lift pump which appears to have a 32mm bolt on the side of it.

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'81 300SD

That is not what holds it to the IP though. That is what holds the pumping mechanism in the lift pump. To remove the lift pump from the IP there should be two or three 10mm (IIRC) on it. Like part 359. You might need a gasket too.

Thanks for the info. Have you done this job before?

My engine stalls after 2 hours or more of driving. Filters are new, valves are at spec and RPM is about 825. I've yet to turn the rack damper bolt(brass finish) in all the way, but was told that the lift pump might be the problem.

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'81 300SD

I removed the lift pump on my 240D because I thought it was leaking and put it back on with a new gasket. Mine only had two bolts and originally the gasket I got was incorrect. There are a few different patterns so make sure you have the correct one. I also just removed the lift pump on my 190DT to remove the IP from the motor. It was easier to do it that way instead of removing all the lines. It also only had two bolts.

Have you checked the fuel screen in the fuel tank? Those are often suspect. Have you had your injectors rebuilt or pop tested?

I think the only time I have heard of lift pump failure was after use in WMO or WVO.

I would be checking my fuel tank vent.

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Every once in a while I get a swoosh sound when I open the fuel cap, this is a ventilation issue, correct? Is the vent on the under side of the car, driver's side towards the back? What exactly am I checking for, and how do I clear it out? Thanks

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'81 300SD

Definitely a ventilation issue. I have no experience with that. Do some searching
Or wait for a response.

I found the tank vent and cleaned it, although it seemed to be fine. I read on another thread that a little bit of suction is normal when removing the fuel cap.

This is a hard problem to diagnose because I rarely drive for more than 2 hours at a time. The engine has been idling a little rough after 30 minutes of driving lately, so maybe that's related to the stalling issue. For now, I'm just keeping the necessary tools on me to raise the idle if I'm a long way from home.

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'81 300SD

After doing some more searching on the forum, I found a way to test the lift pump by gauging the flow of fuel from the return line and looking for air in the fuel. I think that the lift pump is okay. One thing to note is that I installed this engine last Summer with Charmalu and this wasn't an issue with the old engine, so I think that the fuel tank strainer is fine. It's a great running engine with lots of power and starts up cold in the morning on the first bump. It idles well when cold, just having issues once it gets hot after running for a while.

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'81 300SD

I rebuilt my lift pump with nothing more than an adjustable wrench