Picking up an '80 300SD - advice wanted. - PeachParts Mercedes-Benz Forum

Jetmugg · #1 12-05-2003, 04:59 PM

I'm going to pick up my first MB diesel tomorrow. It's an '80 300SD, and has been sitting for about 1 year. The seller said his wife was driving the car and the engine just died, no sputtering, coughing, or clanking involved. After that, he just let the car sit, and didn't try to get it going again (he didn't want her to have the car in the first place). He said it still cranks, and shows oil pressure, but will not start, and he doesn't want to work on it.

Anyway, $500 later, the car is mine and I'm going to trailer it home tomorrow. I have searched the forums trying to learn as much as possible about these MB diesels, and need some advice as to a starting place to get this car running.

What are the most common causes for a 300SD to simply quit running while it's going down the road?

My plan is as follows: When I get the car on the trailer, I will put some diesel fuel treatment and fresh fuel in the tank for the 400 mile tow home. This should "jostle" the fresh fuel and treatment around the tank. Is there a fuel pump before the injection pump, or does the injection pump "suck" fuel from the tank? How about the shut off valve, do they ever stick in the "closed" position?

When I get it home, I'll put a fresh battery in it, and try to start it using the normal procedure. If that doesn't work, I'll make sure that it's getting fuel to the injector pump, and then crack the injector lines to make sure the IP is pumping. I'll check the glow plugs for continuity (is it easy to remove the glow plugs from this engine, or should I leave them in the head and test with a test lead?) If necessary, I will resort to trying to start it while towing behind my truck on a tow strap.

Any other suggestions or ideas? I need to look for the simple solutions first, before getting into anything more esoteric.

Thanks for helping out a new owner.

SteveM.

WANT '71 280SEL · #2 12-05-2003, 06:31 PM

Maybe the timing chain broke? Maybe it just ran out of diesel or something that stupid and he doesn't know how to prime the system? You could get lucky? I don't know what happens when a timing chain breaks other than pistons+valves=trouble. Try to just prime it and put a batery to it like you suggested, you will probably be pleasantly surprised. I am pretty sure that there is no pump before the IP. As long as timing isn't too far off it should start. Well, considering filters, etc. are good. I have a '79 SD like yours but with a 120mph speedometer. You will also be pleasantly surprised with the way it handles on turns. Built like a vault, as long as it isn't rusted too terribly.
Done rambling
David

WANT '71 280SEL · #3 12-05-2003, 06:31 PM

where are you located?
Thanks
David

Jetmugg · #4 12-05-2003, 06:38 PM

I'm in the St Louis area, the car is in Oklahoma. I think you are right, and that I'll be up and running pretty quickly.

Steve.

lietuviai · #5 12-05-2003, 07:05 PM

Just keep us informed when you get it home. We'll all be curious about what you find out.

Wes Bender · #6 12-05-2003, 10:38 PM

Easy to check if the timing chain broke. While someone cranks the engine for you, look inside the oil filler hole and see if the overhead camshft is turning. I hope it is something much less serious, though...

Wes

MS Fowler · #7 12-06-2003, 07:02 AM

With those symptoms, troubleshooting a gasser is much more difficult--could be fuel system, ignition, computer, wiring, or mechanical, etc

In a diesel, its either something mechanical ( like the timing chain), or its fuel related. A much shorter list.

Good luck.

I lived in St Louis for 2 years while getting my Masters degree--love the area.

william rogers · #8 12-07-2003, 03:31 AM

running low on fuel with an alge problem will sure stop them or just a build up of alge in the pre filter.There are a lot of good cars sold for give away prices because of minor problems and owners that have little knowledge of of their machines......

William Rogers........

psfred · #9 12-07-2003, 11:13 AM

The leading cause of sudden failure to run is a leaking suction side hose. There is a lift pump on the IP to pull the fuel from the tank up the the IP and push it through the main filter.

What I would do is the following:

Replace all the fuel lines between the steel tank line and the lift pump. You may have to fabricate the ones on the lift pump as they have steel fittings. You can remove the compression fittings and replace with a hose clamp.

Get new filters. Fill the main filter with fuel before installing, or it will take forever to get the IP full, it has to have pressure in it before it will inject the fuel.

Check the hand pump -- if it is the old red handled one, replace it with the new style thump pump, they don't leak and the old one surely will. If it dumps fuel out the top when you use it, it's allowing large quantities of air in.

Operate the hand pump to make sure you don't have a big leak somewhere -- the hard plastic lines between the fuel filter and IP and the IP an overflow lines can crack. this will spray fuel everywhere and the IP won't work well. If you do have a leak, cut the plastic line off and replace with standard fuel line and clamps unless you want ot buy replacement hose and rittings.

Loosen the return line fitting on the IP and operate the hand pump until no more air comes out before attempting to crank.

Verify that the stop lever is up -- no fuel if not.

Make sure the cam is OK -- remove valve cover to check for a brocken cam or towers --a broken chain will cause valve/piston contact, and this often results in busted cam towers. No other damage.

Oil pump is driven off the crank on this engine.

Could just be out of fuel, too.

My money is on a fuel leak.

Peter

Jetmugg · #10 12-08-2003, 12:43 PM

Thanks for the information guys. This is a super forum.

Here's what I've done so far - bought a new battery and pre-filter. The main filter had to be ordered, so I'll get it tomorrow. I primed the pump with the plunger type primer pump, but I could still see air in the injector overflow lines. As I pumped, the primer pump was leaking diesel out of the pump "shaft". I am concerned that this is the source of air entering my system. I replaced the pre-filter, and tried to prime again. I could not get all of the air out of the pre-filter either. As I pumped the primer, it looked like I was actually moving fuel back and forth through the pre-filter.

I decided to bypass all the filters and the primer pump by plumbing directly from the steel hard line into the IP. However, at this point, I didn't have an effective way to bleed the air out, so I just tried cranking the engine. I cranked for several minutes (a little bit at a time), but I can still see air bubbles in the clear return lines.

The engine has not yet started, but sounds like it's getting close. I get wispy white smoke from the EGR, and a puff or two from the tailpipe, but she hasn't taken the bait yet. The glow plugs seem to be working (at least 3 of them), as the head is getting warm near the glow plugs.

I have cracked the injector lines (at the injectors), and am getting some fuel flow (very little). It seems to me that I should be getting more fuel at the injectors, but I am not a diesel expert. (I'm trying to become a converted gasoline powered gear-head into a diesel-head).

Is the leaking primer pump a sure sign that it needs to be replaced, or is this fairly common.

Any other tips would be very welcome.

Thanks,

Steve M.

JimSmith · #11 12-08-2003, 01:07 PM

Steve M.

There are a couple of items to help calibrate you as you attack this beast and get it running again.

First, the prefilter is never going to be completely full of fuel, and it does not have to be. So, I would put it back in the line to avoid sucking bad stuff left in the tank into your injection pump. This unit typically stays a little less than half full of air, and this is because the system up to that point is a gravity feed system with relatively low flow. So, there is no pressure to collapse the air bubble and not enough flow to draw it into the pump under normal conditions.

Second, the hand pump is, believe it or not, much more efficient at bleeding the system. The injection pump moves a tiny volume of fuel with each engine revolution, and each engine revolution eats a relatively big chunk of battery charge. It is also a big wear on the starter motor, as you are still running the oil pump and overcoming the engine compression. The speed the engine turns over at using the starter just does not pump much Diesel fuel. So you spend half a horsepower of stored electrical energy or so to pump a very small volume of Diesel. You are much more likely to bleed the system of air successfully with the hand pump. As an aside, if the engine spins freely you may have a low compression issue too.

So, if you get a new hand priming pump from FastLane you may improve the performance of the system significantly. I have not installed one but apparently they are much friendlier on the hands to operate as well.

The flow of Diesel fuel at the injectors is pretty small, by intention. The system is a positive displacement system with the injectors acting as relief valves set to pop at a fixed pressure. So, each stroke of the pump for each injector is calibrated to deliver near the exact amount of fuel needed to operate the engine with the throttle in the given position. As you depress the throttle, the injection pump volume per pumping stroke for each injector changes (increases relative to the idle position). While in all likelihood your throttle was set at idle while you made your observations, even at wide open position the flow rate is not all that impressive (calculate the number of injector squirts per gallon of fuel at 60 mph and you find there is a pretty small volume per squirt, which makes us happy because it means we are getting good mileage!).

Nearly all the hand pumps leak when you use them and it is a sign they would be better off retired when this becomes very noticeable and messy. But I have yet to experience one that, even leaking pretty badly, with clean filters and vigorous pumping, cannot purge the system. That is, unless there is another source of air leaking into the system. Check the little cloth covered rubber lines from injector to injector, and look for other leaks. Generally wherever Diesel can leak out, air can leak in if conditions change.

Good luck, and I hope this helps. Jim

Rick Miley · #12 12-08-2003, 01:24 PM

Get a new primer pump. They're $20 at Fastlane. Everyone (except PEH) who has replaced the old one comes back here and raves about the new design. In fact, at least a couple people have reported that their engine quit while driving, and the new primer pump was the only thing needed to fix it.

DCM · #13 12-08-2003, 01:31 PM

I would check the fuel tank filter too. Especially if the car has spent much time sitting around.

My 240d ran odd right after I bought it and when removed, it looked like a large ball of tar. Apparently it had almost stopped the flow of fuel.

Jetmugg · #14 12-08-2003, 02:37 PM

I just ordered the primer pump from fastlane. It should be here tomorrow. I'll keep udating until she runs.

Thanks again for all the information.

Steve

kerry · #15 12-08-2003, 04:04 PM

It's pretty easy to rule out the fuel lines and tank. Get a gallon container and put some diesel fuel or purge in it. Run a line from there directly to your pre-filter and you'll know your pulling good fuel. If it runs under those conditions but not when hooked back up to the normal fuel lines, the problem is back towards the tank.
By the way, make sure ALL the glow plugs are working. Having even one bad plug can sometimes make them hard to start. In fact, I would not go any further with fuel issues before ascertaining that all the glow plugs are working.