W124 300E Fuel Problem-I'm Stumped!

Discussion in 'Engine' started by whysub, Jan 29, 2015.

  1. whysub

    whysub New Member

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    I am very happy with the W124 300E I purchased 4 weeks ago. However it seems to have an issue that has stumped me.

    When I bought it, it had been standing for some months. On my first drive I stopped after a mile or so and put some petrol in it (46 litres worth) as the tank was empty (does anyone sell a car with fuel in it now?). Pulling away from the pump it was very hesitant, and felt like it "fluffing" under load. I thought it could just be the damp,seeing as the car had been unusedfor so long and had been stood all that time in the open.

    After 75 miles or so it was less noticeable, and got better and better and was then running perfectly. I took it out today (it had been parked up for a few days) and it was fine, no hesitancy at all from cold, and it was cold!

    I had to refuel it so put another 46 litres in. Immediately from pulling away from the pump the same hesitancy was there again. It don't think it can be water in the tank, as there would be fuel in the fuel line and injectors would take a few hundred metres to show up. It happened immediately.


    I am trying to think what it could be - the only thing I can think of is it is linked to having a full fuel tank. Any ideas as I am stumped?
     
  2. coalville126

    coalville126 Active Member

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    Almost certain to be condensation in the distributor rather than a fueling issue as you mentioned you drove a short distance from cold, turned off and resumed your journey after soon after.
     
  3. grober

    grober MB Master

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    If there is sediment/rust in the tank perhaps filling it is enough to stir this up such that it partially chokes the outlet leading to fuel starvation? Other possibility is that the tank breather is choked meaning a partial vacuum is being formed as fuel leaves the tank. This effect would be more marked with a full tank as there would be very little " headspace" to evacuate. Easy to test-- just leave the fuel cap loose temporaraily next time you fill up to prevent this vacuum forming. The first "sh*t stirring" suggestion is more likely however.
     
  4. stwat

    stwat MB Enthusiast

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    As well as the above from coalville126, I'll also add that the M103 engine is notorious for eating distributor caps and rotors. When replacing, don't fit cheap crap as they don't last long at all. I made that mistake, twice ! In the end I got proper Bosch items from Mercedes and they have been fine since.
     
  5. John Jones Jr

    John Jones Jr MB Enthusiast

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    Do the simple, basic, cheap and obvious items first. Thus, I'd suggest you change the fuel filter. Add some fuel treatment to the tank too, something like Dipetane if you can get it. Also as suggested inspect the distributor cap & rotor, if in any doubt replace both with Bosch items, they're only usually good for c.60K miles. Both suggestions, even if the issue is not solved are good preventive maintenance and change the OVP relay while you're at it. Total cost should be around £120, money well spent, check eBay both U.K. & Germany for pricing.

    https://www.dipetane.com/
     
  6. OP
    OP
    whysub

    whysub New Member

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    I started up the car from cold and it pulled away from tickover as it should. I then drove for 30 smooth and faultless miles before I refuelled and drove off straight away. It was hesitant from the very first yard. I doubt the distributor could condensate in three minutes, and having removed the tank cap to refuel, the tank would have vented as it should. It only seems to happen when the tank is near full, not when there is about a quarter (or slightly more) full.

    I should add that when it does show this hesitancy, once it gets over 2250 rpm it runs properly, irrespective of how much fuel is in the tank. It will fluff again if I come to a roundabout and have to slow down. Its the fact that it runs properly as it should but then changes immediately after the refuelling, not 200 yards down the road, that gets me.
     
  7. John Jones Jr

    John Jones Jr MB Enthusiast

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    Very possible sediment/crap is being disturbed when refuelling, by the 1/4 tank mark the sediment has resettled at the very bottom of the tank. All the hallmarks of sediment/crap/dirt.
     
  8. coalville126

    coalville126 Active Member

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    I'd still have a look at your distributor cap as you've not mentioned other staring or running issues. An inspection and clean won't cost anything and it's the classic M103 engine symptom.

    Wouldn't disturbed sediment cause insufficient fuelling at higher revs too?
     
    Last edited: Jan 29, 2015
  9. John Jones Jr

    John Jones Jr MB Enthusiast

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    Not necessarily. Of course the problem may not be fuel related but for the price of a filter and twenty mins work...
     
    Last edited: Jan 29, 2015
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  10. optimusprime

    optimusprime MB Enthusiast

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    help

    Please check the seal on the fuel filler cap.
     
  11. Ultrarep

    Ultrarep Active Member

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    Ht leads breaking down?
     
  12. OP
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    whysub

    whysub New Member

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    Thanks for all the replies, some food for thought there.

    I wont be using the car again until Sunday, so if its a sediment in the tank issue, then the sediment will have settled to the bottom by then. It is odd as there have been no starting issues since I've had it, as she starts first turn of the key everytime.

    For what it is worth will check the distributer, plugs and air filter to see what they are like. The car runs perfectly except for this hesitancy issue.

    I will replace the fuel filter before anything else, once i find where it is situated. With my knees, scabbling about under the car is not possible for at least a few months!
     
  13. optimusprime

    optimusprime MB Enthusiast

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    info

    Why , your filter is under the car, just in front of rear wheel it should have a plastic cover over it .The filter is an item that fills up with crud out of the petrol.And is a first priority when you have this type of problem. Also remember the rubber seal on the filler cap,if it is perished ,or it will have splits around the seal ,it can let air in, so you have no pressure in the tank.
     
  14. Bellow

    Bellow MB Enthusiast

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    Anything here of use? The page it comes from refers to 'sedan' so possibly US spec but if you spot any of the components on your car then chances are it's the same. Charcoal canister is part of the re-fueling process IIRC.

    [​IMG]
     
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  15. OP
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    whysub

    whysub New Member

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    My mate just changed the fuel filter for me (my bad knees won't let me scrabble about under the car. The petrol drained from the old filter stank horribly, and was a funny colour. Sadly the car runs no better, but at least that has been changed.

    On reading the helpful comments here, I ordered a new Bosch distributor cap (I didn't want to take the old one of before I had a new one to hands). I also ordered new spark plugs, HT leads and rotor arm to be on the safe side.

    They arrived today so I went out to fit them-five minutes in, it started to rain. Which was lucky as I could not get to the bottom allen bolt in the distributor cap. An allen key was too short to turn, and no room to get an allen key in a rachet in there. as the rain started to come down harder I didn't look any further for a solution. Is there a trick to this, or is it a job of perseverance?
     
  16. John Jones Jr

    John Jones Jr MB Enthusiast

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    I'd suggest that if the petrol is 'off' in colour & smell in the filter, it's got to be 'off' in the tank too. Worth bearing in mind. Fitting the new distributor cap & rotor is a wise move anyway.
     
  17. carat 3.6

    carat 3.6 MB Enthusiast

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    The bottom bolt catches alot of people out. You need to use a set like this, but use a 10mm spanner to turn the hex bit.
    [​IMG]
     
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  18. OP
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    whysub

    whysub New Member

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    On Saturday I fitted a new distributor cap (thanks carat 36 for your removal tip), rotor arm, spark plugs and HT leads and it took less than an hour to do. I replaced the fuel and air filter a couple of weeks earlier. She runs beautifully now-perfect for wafting around in.

    The old spark plugs showed no wear (and didn't look that old), but the rotor arm and distributor cap were well worn and were probably a little overdue for replacement. The HT leads were showing signs of age, and it feels like number 6 is broken internally near the HT cap. A combination of all these things caused the misfire, but I honestly thought it was a fuelling issue, not ignition.

    All I need to do is get the transmission oil changed and I'll probably get the rear diff oil changed too.
     
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