Fuel starvation, 1979 300td, HELP?! - PeachParts Mercedes-Benz Forum

glassman · #1 11-20-2006, 07:56 PM

Hi, All,
I've had my 1979 300td (non-turbo) for about a year. When I got it, with appx.325,000 mi. she ran really well, all things considered (slow, but steady, and would cruise happily at 75-80 on the hiway). Starvation problems began around March, found crumbly lines from tank. Replaced them once , twice, now three times, this time with 5/16 FI line, also all lines up front, replaced both filters twice, cleaned tank and screen, STILL won't run over 40, nor up a hill without gasping.
Today I put a 2 gal. can of diesel where the washer bottle was, ran fuel line from it into another new primary filter, and drove several miles, hoping to discover all was well, and the problems were behind me (or at least behind the fuel filters). No such luck--same problems, although it seemed somewhat better when the primary filter was horizontal instead of upright.
So, can my injection pump be shot? Doesn't seem likely, it revs okay in the driveway, and under light load, like around town. Can the lift pump go bad? If so, is it a lot of trouble to replace? Expensive? Dieselgiant, do you have a pictorial? The primer pump (old white style) doesn't seem to be leaking, it's dry, but maybe?
Please guide me O wizards. It hasn't been so long that I've forgotten how well this car used to run, and it seems there must be some way to make it run well again. Thanks everyone, Dave

vstech · #2 11-20-2006, 10:31 PM

I had massive problems getting the car started... search my threads I've started. and the PO told me it had very low power when it did start, so I started by replacing the loop GP's with pencil and rewired them parallel. then I pulled all the injectors scraped the seats clean of carbon, sprayed tons of PB blaster in the PC's and replaced the heat shields and injectors with a set of known good ones.
the thing Starts in 1/2 a crank and pulls up hills like a rocket... well for a NA 88 hp diesel.
give it a try.
John
oh, and what color is yours?
post some pics.
John

kerry · #3 11-20-2006, 10:42 PM

New primer pumps are pretty cheap. I'd start there.

glassman · #4 11-21-2006, 07:24 PM

Thanks, John and Kerry, I agree the primer pump should be the next thing to try. The car is beige (623, I think) with a greyish beige cloth interior--anybody offering good seatcovers to match those? The car starts right up with no problem, so I hadn't considered the glow plugs. And as I mentioned, around town the car runs fine-- I'ts just on hills, or if I get up over about 35 mph that I get problems.
How about the lift pump? could it go gradually bad? Is it feasible/reasonably cheap to replace? Is it worth trying to find one at a junkyard?
Keep helping--thanks. Dave

barry123400 · #5 11-21-2006, 09:54 PM

Glassman. not that you may not have checked it out. Is the throttle linkage advancing the injection pump arm all the way to the stop when the pedal is pressed? Pretty common failure in my world on these cars. Some even have two small rubbers that dissapear with time giving you about 1/2 speed and no power to speak of as a result. To test for that problem you will notice that when you press the pedal a little there is no corresponding revolution increase until you go deeper with the pedal. The visual inspection of the arm movement requires two people to do properly. I know of cars that have been driven a long time with linkages that were not working properly. In fact if all our members checked theirs out a few would have a problem I think. Oh yes, I forgot to mention with no load the engine would seem pretty good in the driveway as you need far less fuel under that condition. If that does not do it it will not hurt to make sure you do not have a lot of very tight valves. Unlikely from your description but still possible if you have never checked the clearances. I cannot see them producing your particular symptom but strange things happen.