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Discussion Starter · #1 ·
At the moment my 1987 W124 300D is in the driveway and will not start. The engine turns over and the glow plug system appears to be working properly. It looks like the injectors are not getting any fuel. I removed one of the injector fuel lines and turned the engine over .... no fuel came out. The clear inline fuel filter has fuel showing. The tank is more than half full. The engine turns over as normal. This vehicle has always had a small fuel leak from the injection pump. Could the problem be the fuel pump? If so is there any way to test this part to confirm? All ideas?
 

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Your IP leak COULD be the problem, though it is hard to say without knowing where the leak is.

I would consider the IP to be the last possibility, and check both the fuel filters. The pre-filter is the transparent thing inline with the fuel line feeding from the tank. You should be able to see fuel just from looking at it, and it should appear yellowish through the filter. You say you see fuel there, but is it light and yellowish, or is it dark like more of a brown or black?

Next is the main filter, which looks like an oil filter, sitting immediately atop the engine at the front. There is no real good way to check this thing, just assume it is bad and replace it if you have not done so for a while. Anyway, take it off and see if you have fuel flow there. Also try pouring some of the fuel from the filter into a jar to see if it is clean.

If those check out OK, let us know more details on the IP (eg: where the leak was)

HTH
 

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Tony:

What Cracker928 said!

He has been a great contributor on another MB forum if I'm recognizing the handle correctly.

-Scott
 

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Scott,

Yup, dat me. Thanks for the endorsement! I chose the handle because I primarily got into e-maintenance for my Porsche 928, and cracker because I was born and raised in Florida (now in California). My mercedes forum invlovement has grown, but I keep the handle for simplicity.

AJ,

I just realized that I did not really address you fuel pump question, and I don't know if I have an answer. The most common cause for such failure is a clogged filter, and I don't think I ever have encountered a failed pump in a mercedes diesel. I did have a similar no-start problem in my '93 shortly after I got it, but a quick change of the filters, followed by a run of diesel purge solved the starting problem. Is there any news on this issue?
 

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Discussion Starter · #5 ·
Thanks to all for your help. I am back up and running. The problem did appear to be a bad fuel pump. The primer pump is located on the side of the injector pump and was an easy DIY job. Before replacing the pump I checked all the fuel lines and replaced both the spin-on filter and the in-line prefilter. As I mentioned I do have a small fuel leak at the back of the IP, not sure if this is the source, but from time to time I have been getting some air in the fuel delivery system. The fuel pump simply was not getting the job done and purging the air. I replaced the pump last evening and so far it appears to have fixed the "no start" problem.
 

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What led you to the fuel system?

First, I'm a new guy, here, so let me say 'howdy!' to all. I drive an '84 300D with about 187k miles (chocolate brown). I do whatever maintenance and repair stuff I can, but the car still goes to a qualified mechanic for a going over about once a year.

Rivermaster, I noticed you're in Sparta. I lived in Boone for about 16 years in a past life, still got family down there and visit several times a year.

Anyhooo, actually, I have a question for ajcrowe. What led you to the fuel system in diagnosing your problem? Was there anything that tipped you off, or was it just brute force test and elimination of other possibilities? (Hmm. It's not getting any spark! :wink: )
 

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Discussion Starter · #7 ·
First, Welcome roadbuzz to BenzForum!

One of the benefits of a diesel MBZ is the simplicity of the engine. When the car would not start it appeared to be fuel related to me. The engine starter was doing its job, the engine would turn over. I ruled out the glow plug system since the glow plug light did not indicate a problem and most of the time the engine would promptly start without a problem. I found two obvious fuel system problems. One was the fuel primer pump was weak and the other problem was a fuel leak on the injector pump. My theory was that the fuel leak resulted in air in the fuel lines and the primer pump was having a hard time priming the system. If you cranked the engine long enough it would finally start and run OK.

So, I replaced the primer pump, which was an easy DIY job. And this morning I fixed the leak on the IP. The problem was a leaking O-ring on one of the pressure valves on top of the injection pump. This also turned out to be a reasonable DIY project. The following was the process:

You will need a 14 mm wrench for the lines, a 30 torx wrench for the pressure valve holder lock rings, new o-rings and new copper pressure valve seals. You will also need a splined wrench for the pressure valve holders (617 589 01 09 00) is required, there is no substitute.

Clean all the dirt off the IP and lines.

Remove injection lines at injectors and pump, lay aside (no need to actually remove from car).

Remove lock rings by taking the screw out for each pair.

One by one, remove the pressure valve holders. They simply unscrew using the splined wrench. Watch for the pressure spring that sits on top of the valve, it tends to stick in the holder, then drop on the floor.

Remove o-ring from holder, install new one, then use a pick to lift off the copper seal on top of the pressure valve body. Make sure everything is clean, then put a new seal on top, put the spring back in, and re-install the pressure valve holder.

When you have them all in, torque to 35Nm with a torque wrench.

Re-install injection lines, leaving the injector nut loose.

Crank engine until all the air is out of the injection lines. This take longer than you would think.

Tighten injector nuts and start car.

Caveats:

No grit in the IP, make sure EVERYTHING stays perfectly clean. DO NOT pull the sleeves out of the IP if they get dirty, use some carb or brake cleaner to blast the dirt off!

Don't loose the spring inside the pressure valve holder!

If you don't get the torque correct, the seals will leak, causing running troubles but no other damage: Hard knock and rough idle with no smoke, but engine runs fine at high rpm indicates leaking seals. Just retorque the affected holder, should fix it. At worst, you will need another seal.

So far this repair look to have solved my fuel leak and hopefully the no-strart issue. Time will tell.
 
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