First post here been lurking while looking for a w115 to tinker with.

I picked up a 75 300d from a guy about to sell it for scrap. Car is all there and found out the original owner lives about 7 miles from me. Forward ahead.
Car sat for about 5 years, I started draining old fluids and wanted to try and start it.It has the hand primer by fuel filter for reference.

I pulled the fuel lines and pre filter and went straight to to the inlet of the lift pump with my drop down line. When I hand prime it acts like the IP is priming and I can hear a slight squeak. When I try to crank the car nothing and it acts as if the pressure is built on the return line but nowhere towards the injectors. Injectors after some cranking may has a small drop of fuel but certainly no pressure.

So it is like the lift pump is not pushing fuel up to the filter.
I called the original owner. He bought it new and he said all that was wrong with it was it needed a new pump and center bearing. He said he got tired of looking at it and and called one of those cash for cars people to come get it. He did say the car only has 169K miles and based on condition it looks to be right and it was very well taken care of.

So am I missing any tests to confirm a lift pump is bad? Car really doesn't act like it wants to crank at all. Only pulls fuel from my tank if I hand pump. In research it looks like lift pumps rarely fail. Pic of the contents of the fuel filter housing, draining the tank and lines and there certainly was crud.

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Hello and welcome to the forum,

"Only pulls fuel from my tank if I hand pump", do you mean the fuel tank on the car or another fuel source? Did the fuel tank screen look plugged when you drained the tank?

There is a good chance that sitting for 5 years the little springs in the lift pump could be crudded up. Good news is that the rebuild kit from the site sponsor is only $7. If the fuel tank screen was not plugged you could also put everything back together (fuel lines and prefilter) and leave the main filter bowl open like in your picture and with one person cranking the engine you check to see if any fuel dribbles, flows or squirts into the main filter bowl. Wear appropriate safety gear and do not crank for long.

Another problem I have seen is that the seal for the main fuel filter gets pinched and allows the smallest amount of air in causing a no start condition forcing you to bleed the air out f the system via the big bolt on top of the fuel filter.



Here are some other threads:
Rebuild those lift pumps! OM616 OM617 - PeachParts Mercedes ShopForum


Lift Pump Rebuild... - PeachParts Mercedes-Benz Forum

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Marc-André

W115 1975 300D "Geraldine"
W115 1976 300D parts/tutorial car

I am not using the tank right now, Have a temp tank under the hood gravity feeding the inlet side.
Fuel tank screen was nasty but as mentioned not using it as I try to get it running, tank has been drained and blown out as well as the lines so I feel the tank is ready to run.

Other symptom is the return line is under serious pressure after trying to crank, I capped it once and it blew the cap off. Certainly not that type of pressure appearing at the IP.

Thanks for the links, I will do some more reading. I spend about an hour a night reading up on things.

Again I am not opposed to doing some rebuilds of the system but didn't want to chase my tail. The hand primer is leaking under pressure as well so I am sure it is introducing air as well

Don't cap the return line (also called a cigar hose), put it in a clear 4 liter plastic container and watch the flow. The return line gets a lot of feeds: injector return (small black braided line), injection pump overflow (yellow/clear line) and the overflow from the main fuel filter bowl. Capping it would not have allowed anything to move.

Nice looking car, we have the same color exterior, what color is the interior? mine is green. Do you have the foglights?

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Marc-André

W115 1975 300D "Geraldine"
W115 1976 300D parts/tutorial car

tan Interior, green would have been awesome.

the guy (car scrapper) pulled the fogs but is suppose to get them to me.

I did not have it plugged at first, but did to see if I had any pressure.

The car had an old for sale sign in it from when the original owner was trying to sell it 6-7 years ago and when I called he raved about it and was glad someone who like cars got it. Pump was bad was all he said so I took it as it leaked not that it didnt work at all so that was why I was trying to get it to run before I moved to other items.4

I capped it after a while thinking it would allow the system to pressurize. Maybe it is as simple as an oring considering what the Original owner said.

Interior is tan, Green would have been awesome, the guy that picked it up took the fog lights off but is suppose to get them to me. I found the original owners phone number and talked to him for a while getting the history. Title is the original title which is pretty cool.

I need to go through all other parts but wanted to get it running if it would so I could move it around while I worked on it, according to the original owner it was running well until the pump failed so I was not exactly sure if that meant it was leaking or completely failed.

The return line should be open and routed back to your fuel container. If fuel is emerging from the end of the hose while you're cranking, the lift pump is working. The high pressure to the injectors comes from the pumping elements, the only way to prime them is by cranking once you have the IP primed. If no fuel is being delivered and you know the lift pump is pumping, the fuel rack is possibly seized.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Thanks, always super helpful hearing from experience.
It only pumped out the return line into my tank when I was hand priming as well as turning by key.

I will go back and start over tomorrow and check to see if fuel it going into the main fuel filter. A seized rack sounds more plausible due to it sitting. Funny the old man was defending the car (I Did say hey you aren't selling it I didnt want the guy who picked it up to crush it) and how well it ran just got tired of looking at it so I feel it is simple, just I am missing it.

If fuel was coming out of the return line when you were cranking the engine, then the lift pump works. The lift pump sucks fuel from the tank (or bucket/jar/jug in your case), sends it through the fuel filter, through the injection pump fuel gallery, then through the pressure regulating valve (the squeak you hear when priming by hand) and into the return line. The lift pump DOES NOT send fuel to the injectors, the only way to get fuel into the hard lines and to the injectors is for the pumping elements to be operating (engine rotating) and the fuel rack moved to a position to allow them to draw fuel. It isn't unheard of for a car that's sat to have a seized rack, especially if there was water contamination in the fuel or it was running on WVO.

If the rack is seized, you're better off sending the IP out for rebuild or sourcing a known-good second hand one (post in the parts wanted section of this forum). The possibility of the rack sticking in a wide open condition is quite high and can cause a runaway (it happened to another guy on this forum not too long ago).

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

To get fuel to the injectors:

1) Disconnect the hard lines at the injectors (17 mm flare wrench), and loosen the nuts on the hard line brackets (8 mm wrenches).
2) Unplug the glow plug harness (to save battery charge).
3) Use the primer pump to purge the air from the clear plastic hard lines.
4) Crank 30-45 seconds, wait 10 minutes to let the starter cool off, repeat until fuel dribbles out of the rearmost metal hard line.
Be patient, and take your time...you don't want to fry your starter. (I watched some Netflix shows between the cranking sessions.)
5) Tighten the hard line fitting (17 mm) on the rearmost injector.
6) repeat step 4) and step 5) until each of the remaining injector hard lines are reconnected. They fill from the rear to the front (ie 5, 4, 3, 2 and then 1).
7) Re-tighten the injector hard line brackets (8 mm).
8) Reconnect the glow plug harness.

Glow twice for 45 seconds, depress the accelerator pedal and crank the engine.
The engine should start right up, if the series glow plugs are okay.

If the rack is seized, be ready to pull the feed hose out of your mini tank, in case the engine starts to run away.

PM me if the primer pump is bad, I have two good spares.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Thank you so much. I thought it may be in fuel shut off position as I had a cummincs do that before. I will go through some tests tomorrow to verify. With the original owner saying the pump was bad I feel it is the IP but wanted to give it a go anyway.

perfect thank you. I know I did not follow that procedure.I felt like the lift pump was bad but now that I know how to check I can move past that once I confirm, just no pressure at all at the bajo bolt going into the primer and filter made me believe it was bad, that and it wasn't sucking fuel from the tank while cranking.

Again I really appreciate the help. I did the prime method here and had better fuel at the last two then yesterday so I was optimistic. Did the entire rail and let it glow a few times and nothing.

Then had a moment, I grabbed a battery out of the garage and thought it was spinning slow even running on a charger. Went and grabbed a 900CCA battery and turned the key for about 15 seconds and it fired right up. Runs super strong and solid and held a nice idle.

Now on to getting it squared away.
The Hand primer leaks pretty bad.

The throttle linkage is not fluid from the pedal as if it is sticking.

The hand throttle works well.

Lift pump does appear to work fine.

There is no vacuum on the shot off so it doesn't turn off with the key, you have to press down the shut off manually.


Car smoked at first but was super clean on next few crankings.

In my neighborhood I have always noticed a house with 4-5 300Sd's in the driveway, I managed to catch him outside and talked for a while and he has a deep love for Mercedes Diesels and has a W115 300d himself that he is working on. He came over and was amazed at how the engine sounded and how tight it was so I have been more energized to get it road worthy for sure now. Now to order fuel lines, brake parts etc and get it going.

Congrats on getting your 75 W115 300D to run after sitting for 5 years.

Definitely replace the hand primer pump, as air incursion there will cause poor performance and difficulty starting (while the IP slowy gets air bound).
MB Part Number 000-091-11-90.
If it is NLA, I do have two good used spares.

There are quite a few pieces to the engine control mechanism.
Dry parts can easily bind and cause erratic performance.
On the linkages, I use ATF to lubricate the ball and socket pivot points.
Additionally, I use DeoxIT Marine Mechanical grease on the shaft pivot points.

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

I may do a rebuild thread on the car but wanted to share some updates.
Fuel lines have all been replace with the tank cleaned. Also Decided to install an electric fuel pump while back there.
Traced about 8 broken vacuum line connections which when fixed now the car shuts off with the key.

Still dealing with a sticking linkage system. I greased all ball joints and have hit all pivot points with lub daily for a week. Seems to be frozen under the exhaust manifold so May pull it off and see what is up, either that or the spring at the firewall is too weak. Don't like it starting up then going WOT right away when I hit the pedal.

So far everything is looking pretty good, cranks up very nicely and leaks about a quart of fuel from the primer so once that gets here I think diesel leaks will be resolved.

I rebuilt the brake calipers and once I get new front pads I will bleed the brakes and should be able to stop it for a maiden run.

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