the car is my daughter's but I am taking care of it for her. It will run fine then sometimes have no power and be hard to start.

I changed the primary filter a month or so ago and the air filter and treated the fuel with a biocide.

I'm thinking to treat it again to start with.

What are the symptoms of a worn lift pump?

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I would imagine a worn lift pump wouldn't affect starting too much, but would be pretty predictable and replicable while driving. If the car sat for a while you might want to take a boroscope and look in the tank. Not only fungus but it's possible rust got in there I imagine. Honestly id just pull the tank screen and take a look, it's not too difficult.


Sent from an abacus

__________________
TC
Current stable:
- 2004 Mazda RALLYWANKEL
- 2007 Saturn sky redline
- 2004 Explorer...under surgery.

Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

Intermittent pretty well lets out the mechanical side. Our MB's usually work or dont.

You might consider pulling the tank and having it flushed. The borescope is a good idea too.. get an idea whats happening in the tank

__________________
1985 300D 198K sold
1982 300D 202K
1989 300E 125K
1992 940T

"If you dont have time to do it safely, you dont have time to do it"

"The democracy will cease to exist when you take away from those who are willing to work and give to those who would not."

When its not working properly try opening the fuel cap. Maybe the vent isn't working properly and is causing a vacuum in the tank.

__________________
2004 F150 4.6L -My Daily
2007 Volvo XC70 -Wife's Daily
1998 Ford F150 -Rear ended
1989 J-spec 420SEL -passed onto its new keeper
1982 BMW 733i -fixed and traded for the 420SEL
2003 Volvo V70 5 Speed -scrapped
1997 E290 Turbo Diesel Wagon -traded for above
1992 BMW 525i -traded in
1990 Silver 300TE -hated the M103
1985 Grey 380SE Diesel Conversion, 2.47 rear end, ABS -Sold, really should have kept this one
1979 Silver 300D "The Silver Slug" -Sold

M first step is Startron and filters. My 85SD went from not starting to running fine with that process.

__________________
85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Dude 99s suggestion is a cheap starting point. The consistency being when the car is turned off the existing vacuum in the tank may pull the fuel back a little creating harder starts. Or when the vacuum accumulates enough the engine is being partially starved.

Of course it can be other things but this is probably the easiest to check . Usually changing the fuel filters is always the first step with any suspected fuel supply issues though. Filters can fool a person in their behavior sometimes.

Much depends on if you are getting her to check things or doing it yourself. Leaving the fuel cap loose may be messy. As a test just drilling a 1/16 inch hole in a spare old fuel cap you have around might be used for a test.

Hard for this design of lift pump to become intermittent. Not impossible just unlikely in my opinion. Air leak into the system of a semi intermittent nature is a possibility as well I suppose.

You have been around these cars for a long time in comparison to most members. There is a fair list of possibilities. Some are just less probable than others. If she only experiences the loss of power after driving a fair total distance also increases the tank vacuum possibility quite a lot. On a totally obstructed tank vent the car will usually totally shut down in about 100 miles after fueling with a strong lift pump. With a less than totally obstructed tank vent running time until power decreases may not be that great a distance. Especially if the lift pump has lost some efficency with age. The primary problem still would be the tank vent.

The majority of these cars are still on their original lift pumps with original valves I suspect. They are not technically really bad. I suspect they are still quite serviceable but just do not pull as hard nor develop their original output pressure. They should be tested for their pressure output every few years. Few ever are.

Thanks guys. I'll check the fuel cap, treat the tank and change both filters....in that order.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

This is my bet. Source could be the primer pump or some other leak in the engine bay. Diesel fuel will fluoresce under black (ultraviolet) light, so you can start with that and maybe pressurize the system to make the air leak into a fuel leak.

__________________
Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

If the 300SD is acting up, you need to place her in the corner for a few weeks.

__________________
daw_two
Germantown, TN

Links:
Sold last car --- 05/2012 1984 300D Light Ivory, Red interior
Cluster Needles Paint
New Old Stock (NOS) parts

Past:
3/2008 1986 300SDL "Coda"
04/2010 1965 190D(c) "Ben"
& many more