124 E300D rough running - PeachParts Mercedes-Benz Forum

carreraplanes · #1 05-07-2017, 07:53 AM

Bought a 124 E300D 1994 recently. Ran fine except for faulty tach. Removed the OVP and re soldered the joints as per this you tube clip: https://www.youtube.com/watch?v=zPSSXSVMiJk

Started the car, Tacho working fine and it started easier from cold. Took it up the road. All seemed fine for a couple of miles then it started running rough when under load and throwing what I take to be diesel smoke out the back. Drove it slowly back home. Removed a working OVP off another car. Same problem. Tach still working but rough running under load. Worried if my repair on the first OVP was rubbish, and it's failed wrecking the electronics it's supposed to protect. Wife will be going ape in a moment as she is supposed to be driving it to work tomorrow

Dmitry at Pelican Parts · #2 05-08-2017, 07:03 PM

Take a look at the link below, it's a DIY guide on addressing the OVP issue that you're having and don't forget to check out our other DIY articles on the W124 platform. Please let us know if you have any questions!

Mercedes-Benz W124 Over Voltage Relay Replacement | 1986-1995 E-Class | Pelican Parts DIY Maintenance Article

carreraplanes · #3 05-08-2017, 07:21 PM

Thanks Dmitry, will look it over

jake12tech · #4 05-08-2017, 10:27 PM

What color is the smoke? The OM606 is common for fuel leaks, and sucking air. Look at the clear fuel lines. See if they're sucking air at idle or under load (Rev the engine to at least 2k). Most common leak points are the fuel lines, o-rings, SOV & delivery valves on top of the pump.

Also, did it start after you last filled up? Fuel filters ever been replaced??

carreraplanes · #5 05-10-2017, 08:56 AM

Thanks for your help and advice. Went over the hoses and connections for a second time and found that the small fabric covered pipe that runs from the filter and disappears under the black cover over the cam cover is saturated with diesel. Wondering if a leak here would introduce sufficient air to cause rough running

Please see photo below.

Not sure what it attaches to under the black cover, maybe a sensor or something

I guess I need to replace it and then bleed the system to eliminate this as the culprit

Diseasel300 · #6 05-10-2017, 09:06 AM

That's the return line from the injectors. There's a short "jumper" of that type of hose bridging the gap between each one. You need to buy a length of hose and make new ones, not a difficult job.

I wouldn't expect that the cause the problem though since it's on the return side. Being an OM606, I'd more strongly suspect O-ring seals in the lift-pump side of the fuel system to be a problem.

carreraplanes · #7 05-11-2017, 06:20 PM

Thanks, I'm going to service the filters and if the problem still persists that would be the next port of call...

carreraplanes · #8 05-14-2017, 06:09 PM

Screen in tank, pre filter, and main filter all changed, still no power off idle, so it's on to the O rings in the lift pump side of the fuel system.

Have searched this forum and the 'net in general for a procedure but can't find anything. I'm probably using the wrong search terms.

Wondering what I need to do physically and what parts I need to order??

Maxbumpo · #9 05-15-2017, 12:35 PM

That leaking fabric covered line needs to be fixed! Don't ignore that. That line is one of six that are daisy-chained from #6 injector all the way back to the one you pictured. You need one meter of the fuel line (part # 605 078 0581). They are return lines from the injectors - the fuel injection pump pushes extra fuel to all the injectors to cool them, and recycles that to the injection pump. If they leak fuel out, they can leak air in, which is not helping your situation.

Maxbumpo · #10 05-15-2017, 12:50 PM

I'm looking up the part numbers for the fuel system o-rings. Here's a diagram showing all their locations.

carreraplanes · #11 05-15-2017, 03:59 PM

Thanks Max, that would be a great help. Yes I was going to replace the fabric lines and the transparent ones too and any other perishables that may help, also wondering if the lift pump itself might be suspect?

Zulfiqar · #12 05-15-2017, 04:47 PM

you cannot buy the O rings for the plastic tubes from mercedes. You can buy them from an industrial O ring supply place though. But that only works if the lines are still serviceable, if they are cooked a dark brown color - replace them.

to remove them - press the horseshoe inwards to unlock the line. Do this on a hot engine and replace 1 line at time and fire the engine after every line. this will prevent air locks in the system.

Get a can of lubro moly purge and clean out the fuel system, you will need to disconnect the feed line which is buried under the intake manifold (its tightened to the fuel heater in the head)

Maxbumpo · #13 05-16-2017, 09:53 AM

Quote:

Originally Posted by Zulfiqar

you cannot buy the O rings for the plastic tubes from mercedes. You can buy them from an industrial O ring supply place though.

That's funny, I just bought them from one of the online dealers last year. I'm sure that one can also get o-rings that will work from a number of other sources, but there may be some back-n-forth and delay because you'll have to take the old out, measure, and then get the new o-rings.

I'm not having any luck finding my list of part numbers, I'll keep looking though.

carreraplanes · #14 05-16-2017, 07:11 PM

Hi Max,

I think I found the part numbers that go with your diagram:

Mercedes-Benz Teilekatalog (Ersatzteile online)

From your mark up I think I need O rings 35, 38, 68, 89, 110, 122.

But my pipes are yellowish so do I need all of the following: 32, 65, 86, 119, 146? There is also another line that is not numbered on here, the middle line of the 3 that go into the filter housing, not sure if I would need that if I could get hold of it?

I'm also wondering if I should apply a repair kit to the lift pump

Also is there anything else I might have missed

Thought I might just email the diagram and parts list to Mercedes and then just scrabble about for what they can't supply.

Many thanks,

Keith

Maxbumpo · #15 05-17-2017, 08:10 AM

Well, on my engine I can hardly see those pipes with the intake manifold in place, so I've never changed them. About 379k miles on that car now. However, they are not too expensive so go for it if you like.

I would not mess with the lift pump unless you have performed some test to diagnose that it has failed. Again, your choice. In my opinion that is asking for trouble ("fixing" something that you are not sure needs fixing). Some have offered that a weak lift pump can be diagnosed by pinching off the fuel return line (that goes back to the fuel tank) and if there is any improvement in engine performance, than your lift pump is suspect.