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  #1  
Old 04-07-2019, 06:51 PM
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New to me W126 300SEL Not running well at all

Hello everyone,

Never have been on this side of the forum. I have 3 w123 diesels, but this is my first older gasoline mercedes to mess with.

I will upload pics of it later when i get back into my Flickr acct.

White/Grey, 1989, 300SEL, 188k miles. A friend of a friend messaged me yesterday asking if i wanted it since he knows i like these older mercedes.

$700, clear title

Paint is excellent. Body has some minor dents.

Front seats are pretty ripped up, power functions work. Rear seats are perfect.

Good suspension components. No fluid leaks.

A/C, not sure, Blower motor wont work.

Here's the big issue i need help with ( i know it could probably be a slew of things)

The car runs terribly. No overheating or anything, but upon cranking it, it idles smooth for a second, then starts surging and such. If you *lightly* give it throttle, it will actually smoothly rev up to 3000 RPM, and sounds excellent doing it. But anything over that, it stutters and dies.

The longer it sits running, the worse it gets. Surging when idling, etc. If you really give it some throttle, it will either die, or drop to about 500rpm and idle bad until you give it some light throttle.

So i know it has been sitting since 2010. Very first objective is to drain every bit of 9 year old gasoline out of it, and inspect the tank. Will need to look into how i go about doing that.


Then i guess i need to inspect all fuel related filters, etc.


Also- need to check fuses.

I just got the car home last night, and its been pouring down raining. SO i haven't really gotten off in it.

Who knows, it has a 1/4 tank of 9 year old gasoline in it. But it was only $700

Any tips from anyone that has more experience than me with the m103?

Thanks!
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'89 300SEL
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  #2  
Old 04-07-2019, 07:17 PM
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I am sure that you probably would have preferred to drain the old gas before running the car which would have been a good move. I would recommend that you drain the tank, change all of the fuel filters and go from there. The fuel tank may need to be flushed. Probably a good idea to replace any rubber fuel lines also. Good luck.
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  #3  
Old 04-07-2019, 10:56 PM
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Do a compression test first. Fresh set of plugs unless they look great, regap the old ones if reusing.
Drain the fuel as discussed, put in Techron or some other high quality cleaner with a TopTier premium fuel.
Change the oil and filter, I'd suggest a 15W-40 diesel C rated dino version.
Run it and see how it reacts.

Good luck!!! And........waitin' for the pics, those are nice cars!!!
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  #4  
Old 04-08-2019, 02:45 AM
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Yeah, i would have rather drained all of the old fuel out, but oh well.


Going to get to work on it ASAP. Anxious to find out how much new fuel, a clean system, and new filters help.

Pics! Keep in mind, it hasn't been washed in years

20190406_133516 by Daniel Inman, on Flickr


20190406_180742 by Daniel Inman, on Flickr

20190406_133537 by Daniel Inman, on Flickr

20190406_133533 by Daniel Inman, on Flickr
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'83 240D 4spd
'83 240D Slushbox
'83 300D + Mud tires
'83 300SD
'89 300SEL
'00 CNG Crown Victoria
'10 E63
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  #5  
Old 04-08-2019, 08:16 AM
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Nice score. A classic MB beast. Welcome to the dark side. Haha.
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  #6  
Old 04-08-2019, 08:46 AM
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Just beautiful. Get it running right and I bet that you will never sell it.
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  #7  
Old 04-08-2019, 09:43 AM
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Sweet looking car and a good score.
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Old 04-08-2019, 02:18 PM
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Congratulations! Sounds like my 88 when I got it. Only 2k miles in the 10 years before me! I even have the same white and grey!

After the tank got flushed, a few fuel lines replaced, some Sea Foam and a can of BG BK 44 it got better. I also replaced the plugs, plug wires, fuses, and distributor cap.

Once I started to drive the car regularly, there were some hiccups once in a while which I just thought was some more that came loose. For the last three years it has been very smooth and the mpg's even got better.

Just a reminder - the 300SEL runs high rpm. ~3000 rpm @ about 60 or 65!
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Old 04-08-2019, 03:04 PM
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Perdy
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  #10  
Old 04-08-2019, 04:54 PM
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dinman, consider replacing the coil definitely the ignition wires, spark plugs, distributor cap & rotor, plus the O-ring on the distributor back plate and Oxygen sensor.
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  #11  
Old 04-09-2019, 10:49 AM
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Check all the vacuum lines and the rubber booth underneath the fuel distributor for leaks.
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  #12  
Old 04-09-2019, 12:18 PM
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di:

In the case where a K-jet injected engine has been in regular service and is running poorly, the advice would indeed be to first ensure that it has good compression and that the ignition system is in good order. In this case, however, where the engine has been out of service for nine years, the first order of business is to clean the fuel supply system of all the old gasoline. This may be done by first draining the tank of old fuel, then adding about 5 gallons of fresh fuel. With the fuel pump relay removed, the pump sockets may be bridged to cause the pump(s) to run continuously. The continuously running pump(s) will circulate fresh fuel through all the supply and return lines, the filter, and a portion of the fuel distributor & pressure regulator. After about fifteen minutes of pump running, a change of the main filter is in order, and another fifteen minutes of circulation. If fortune smiles, when the engine is next started, fresh fuel will make its way to all the nozzles, the metering plunger will be free, and the EHA orifices will wash out.
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  #13  
Old 04-10-2019, 08:09 AM
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Thank you everyone!!

Frank, i wish i would have seen your post earlier.

I just got done replacing the filter and draining the tank, that filter was terrible.... The filter element looked like it had come apart and it looked like apple sauce coming out of the end..
New filter and 3 gal of fresh 93.

Running marginally better, but not good.

So it cranks up great, rpms fluctuate a little when idling, if you softly rev it up, it revs smoothly. If you give it any more than say, 5% throttle, it pops / misses/ shakes / etc. Then bogs down to ~600rpm.

Here's a video

https://youtu.be/MDspqp_PFK8
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  #14  
Old 04-15-2019, 09:01 AM
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Ok, I'm back with some more results I suppose

This weekend, I pulled all 6 injectors and cleaned them, and also all 6 plugs and replaced them.

Car idles much much better than before, but still not in driving condition.

It cranks up pretty good, when cold you have to feather the throttle a little and it may die on the first start up.

If you lightly give it throttle, it will rev flawlessly to 3-3500rpm. As soon as you give it more throttle, it starts backfiring / fluttering/ dying. It's like it's not getting enough fuel for the amount of air being ingested.

When under load, in a gear, it's gutless. The fastest I can go uphill is maybe 2-5mph. Downhill, 30mph.


https://youtu.be/gQBwrDfDok8

Could the pump be clogged from the nasty fuel?

My next two missions are to replace the pump and inspect the tank strainer in the bottom.

Any tips?

Last edited by dinman; 04-15-2019 at 09:22 AM.
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  #15  
Old 04-16-2019, 04:19 AM
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dinman, before replacing the fuel pump try running it out of the car. Do a Search on "fuel pump". I recall reading a thread about cleaning a fuel pump with kerosene, using a battery to briefly power the pump.
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