Rough Running 1981 300D - PeachParts Mercedes-Benz Forum

i-osprey · #1 11-26-2008, 10:10 PM

I had already planned a valve adjustment on this car for the upcoming weekend when I ran out of diesel.

My fuel gauge is a little iffy when it gets low and I had been driving rental cars a lot the last two weeks so I wasn't paying attention to my trip odometer.

So, I had some transmission fluid under the hood that I filled up the fuel filter with. Once primed, it ran OK but then I ran out again before I could get to the gas station.

I was also out of transmission fluid.

But I did have some motor oil.

I then filled up the filter with motor oil and cranked to my heart's content only to have it never start and keep running. It would smoke a bit but never actually started and ran.

I bit the bullet and walked to a station, bought a small fuel tank and brought a gallon of diesel back.

I fill the filter with diesel, put the rest in the tank and started the engine pretty quickly thereafter.

I noticed that it runs much rougher now when in gear at a stop. If I put it in neutral it smooths out but overall it still runs rougher than it did before my alternative fuel experiment.

Today I replaced the fuel filter and filled it with Diesel Kleen.

The roughness is still there.

My question is about my injection pump. Could I have damaged it or thrown timing off with the motor oil?

Accompanying the roughness of the engine is a pinging. I think it's a valve or two but I'm not that knowledgeable about how that sounds.

I will be adjusting the valves as soon as possible, maybe even tomorrow, to see to what extent that will fix the problem. I will also do a diesel purge with the Diesel Kleen in a bottle technique.

Any ideas how/if I complicated things beyond needing a valve adjustment?

TIA for the help

ARNOLDLewis · #2 11-27-2008, 01:41 AM

Keep gas out of it first off. J/K maybe air traped somewhere. bleed fuel system??or maybe botom of tank had water in it and your filter is full? I know if your injectors get a shot of water they hate it.good luck I'd check the filter first.

BoomInTheTrunk · #3 11-27-2008, 02:01 AM

mine does the same thing with the fuel gauge and i have to ran out of fuel. The sending unit is gummed up and needs to be removed and cleaned out, read up on how to do that. As for running poorly you have air in the system. Crack the fuel lines at the injectors and put vacuum on the fuel shutoff, then crank the engine to get all the air out. There will be fuel going everywhere to make sure to put towels under the cracked lines.

i-osprey · #4 11-28-2008, 12:12 AM

Quote:

Originally Posted by BoomInTheTrunk

mine does the same thing with the fuel gauge and i have to ran out of fuel. The sending unit is gummed up and needs to be removed and cleaned out, read up on how to do that. As for running poorly you have air in the system. Crack the fuel lines at the injectors and put vacuum on the fuel shutoff, then crank the engine to get all the air out. There will be fuel going everywhere to make sure to put towels under the cracked lines.

I should loosen all the lines at the injectors and put vacuum on the fuel shutoff?

How do I put vacuum on the fuel shutoff? I don't even know what you mean by the "fuel shutoff."

I replaced the screw-on fuel filter and the plastic pre-filter under the hood today.

I also loosened the injector lines one by one while the engine was running to try to get out the air that way but it didn't work.

BoomInTheTrunk · #5 11-28-2008, 12:21 AM

dont worry about the fuel shutoff. You might have a air leak somewhere. When my car ran out of fuel my primer pump went bad and started to suck in air. the primer pump is that white thing down under the injection pump to the left. If the fuel system is sucking in air then you need to find where to fix the problem.

i-osprey · #6 11-28-2008, 12:25 AM

Quote:

Originally Posted by BoomInTheTrunk

dont worry about the fuel shutoff. You might have a air leak somewhere. When my car ran out of fuel my primer pump went bad and started to suck in air. the primer pump is that white thing down under the injection pump to the left. If the fuel system is sucking in air then you need to find where to fix the problem.

So, if I don't have an air leak the way I did it should have eliminated the air?

I have never used that primer pump until the day I ran out of diesel so I may have loosened up something.

I used it again today and it worked to prime the plastic filter but I did hear some air sucking in or out after a few strokes.

Is there a way to tighten it enough or should I just replace it? I just checked it and when I pump it it leaks very badly from the top. I also noticed that the white plastic filter is at least half-way full of air.

Also, the other day the engine didn't shut off immediately after I turned off the key. There was about a second delay. I have noticed a slight delay before also.

What did you do?

BoomInTheTrunk · #7 11-28-2008, 12:33 AM

you have to replace it, get the new style primer which is the black one that you dont have to unscrew.

i-osprey · #8 11-28-2008, 12:36 AM

Ok, I just ordered that from ********az.

The other day I noticed that there was a delay before the engine shut off also. I turned the key off and stepped out of the car before the engine shut off.

Could this be related?

BoomInTheTrunk · #9 11-28-2008, 12:38 AM

That would be a vacuum issue. Either you have a lack of vacuum or a bad(going bad) fuel shutoff. The fuel shut off is that round thing on the injection pump with the vacuum line going to it.

i-osprey · #10 11-28-2008, 12:47 AM

Quote:

Originally Posted by BoomInTheTrunk

That would be a vacuum issue. Either you have a lack of vacuum or a bad(going bad) fuel shutoff. The fuel shut off is that round thing on the injection pump with the vacuum line going to it.

I'll double check that I haven't knocked any vac lines loose when I was banging around in there first.

I have a mighty-vac, or the Craftsman version anyway, so I will do a check with it.

toomany MBZ · #11 11-28-2008, 04:07 PM

BITT is correct, the delay in shutting off usually is a lack of vacuum. Yet I had a shut off valve fail, check for oil in the hard brown vac line, even when it shut down instantly, at 10 inHG when I used a mity vac on the valve itself.
There was oil dripping from my ignition switch, which I didn't know until I removed the kick panel, oh what fun!
My fuel gauge, in the SD, is also not registering low fuel, you may be able to take out the sending unit and clean it up, or as I did on a 123, replace it.
To remove the sending unit (immersion tube indicator in MB speak) on a 126, you need to remove the rear seat bench and back. Not so in a 123, just under the first aid kit. Two screws, and pull slightly up and toward you as there are plastic tabs in the back.
You may have a low idle, is there a black flat plastic knob on the dash? If so, that is an idle speed adjuster.
Good luck, and keep us posted.

i-osprey · #12 11-28-2008, 08:08 PM

Quote:

Originally Posted by toomany MBZ

BITT is correct, the delay in shutting off usually is a lack of vacuum. Yet I had a shut off valve fail, check for oil in the hard brown vac line, even when it shut down instantly, at 10 inHG when I used a mity vac on the valve itself.
There was oil dripping from my ignition switch, which I didn't know until I removed the kick panel, oh what fun!
My fuel gauge, in the SD, is also not registering low fuel, you may be able to take out the sending unit and clean it up, or as I did on a 123, replace it.
To remove the sending unit (immersion tube indicator in MB speak) on a 126, you need to remove the rear seat bench and back. Not so in a 123, just under the first aid kit. Two screws, and pull slightly up and toward you as there are plastic tabs in the back.
You may have a low idle, is there a black flat plastic knob on the dash? If so, that is an idle speed adjuster.
Good luck, and keep us posted.

Thanks for the good info.

I was expecting to have to remove the tank from the car to clean the sending unit.

I'll do that ASAP.

I am pretty sure that I have an air leak problem. The white plastic filter under the hood is over half full of air.

I will install the primer pump when I get it.

I will check the idle control knob but it really is running rougher now than it was before I ran out of fuel and had to use the primer pump for the first time.

toomany MBZ · #13 11-28-2008, 08:55 PM

I think you're right about the air leak, there is usually a bubble in that (primary) filter, but not as large as you describe.
It's possible to have an air leak without a fuel leak at the same spot.
Does that filter have any "gunk" in it? Mine does, but not enough to cause promblems.
Check your fuel lines also.

i-osprey · #14 11-28-2008, 09:37 PM

Quote:

Originally Posted by toomany MBZ

I think you're right about the air leak, there is usually a bubble in that (primary) filter, but not as large as you describe.
It's possible to have an air leak without a fuel leak at the same spot.
Does that filter have any "gunk" in it? Mine does, but not enough to cause promblems.
Check your fuel lines also.

I replaced the plastic filter after I did the diesel purge. It did have little bits of black gunk in it. It actually felt like metal but I didn't put a magnet to it. I also found this same gunk on the sending unit when I pulled it earlier.

I cleaned it out, reassembled it and installed it. I have 3/4 tank now so it will be a while before I know if it works.

I noticed what looked like corrosion on the lower portion of the thin wires so I may have the same problem as before. I tried very gently to scrape off the gunk but I wasn't brave enough to scrape very hard so most of it is still there.

I will also be replacing the tank strainer when the fuel level gets low enough to do so. Do you recommend cleaning the tank? Is there a way to do it with the tank still in the car? I was hoping to find a way to use the sending unit opening and the tank strainer opening to clean it and drain it while it's in the car.

I don't know how much gunk is in there but there was some in the sending unit and it has very small holes so there is probably quite a bit in the tank.

BoomInTheTrunk · #15 11-29-2008, 03:35 AM

if you have access to bio diesel that will clean the tank out real quick.