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My mercedes has developed a flat spot in that when trying to pull away at roundabouts, etc it has very little power until it manages to pick up. It does not do it all the time. Sometimes it will also just cut out when I slow down (although not very often), although it always starts immediately again. I have taken it to a garage twice but they couldn't find any thing wrong with it. Any ideas? Thanks a lot
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pops
Most of the misfire/running faults on these are down to the distributor cap. Some cars just seem to eat them. There's often nothing visibly wrong - they just break down their insulation under load and short the spark to earth.
Get your garage to compare the spark power coming in from the coil to the spark going out to the plugs. If there's a big difference, change cap and rotor. For once; don't use genuine parts. They appear to be both over-priced - and water-permeable.
If that black conductive-plastic RF-radiation shield has deteriorated and looks, in any way, burned or scorched; either replace it too, or cut the whole centre out to keep it well away from the leads.
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Try the simple things first, but be aware that various MB models built between 1991 and 1995 suffer from the breakdown of insulation in the wiring harness/loom. This is often not visible until additional covering materials have been stripped away. It sometimes manifests itself in the sort of problems you describe. You'll see lots of commentary at:
tinyurl.com/8nx7v
where you will see that it is not just an M104 engine problem, as is commonly thought.
I do hope that this is not the case for you, as a replacement loom costs about £450, plus fitting (which some reckon should take no more than two hours at most).
There's a long thread on this in the W124 section of the MB Club forum, including some horrific photographs of broken insulation in places normally buried in covering tape and resin. It seems that MB changed to an eco-friendly insulation material, which has proved to be not up to the job. In extreme cases, this has resulted in zapped ECUs.
www.mercedes-benzownersclub.co.uk/
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Many thanks for your reply. I'll look at the mb club too. Cheers
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Hopefully this will be the problem. I don't use genuine parts anyway as it's too expensive and and old car. Thanks for your help
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Not sure how good your garage was. I might suggest 2 approaches.
1. Although I am against the 'replace every part till it is fixed' approach, with garage costs so high, IN THIS CASE it might work. Replace the spark plugs, distributor cap, rotor arm, ignition leads, ait filter. At Euro Car parts perhaps the cost = 1.5 hours of garage labour. At least they can then be discounted. Replacing these parts anyway is no great loss. MPG will increase.
2. Take it to a Bosch centre and get a good Bosch Trained Technician to put it on the machine and rolling road. A good man should find the problem. He might then replace the above parts!
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Thanks for your message. I'll look into your ideas. Cheers
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I would be interested in the solution. You could get all the bits, maybe £70, and replace one at a time,. Have a run and see what works. Then replace the lot and feel satisfied you may have cheated the garage, done it yourself, and it will not need redoing for ages.
Good luck
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This would be a W129 with the M103 engine would it? (Engine type on plate on slam panel).
These are fitted with KE-Jetronic 3.5 and I would suspect some problem with this, rather than the ignition (unless it is obviously missing).
You could try thoroughly cleaning the meter head mechanism and making sure that the brass plate moves smoothly within the aluminium 'venturi'. When you press it down a cm or so it should rise smoothly back up and come to an abrupt stop. Clean the whole area with carb cleaner.
You could also clean all the idle air pipes and the warm up idle air valve. Check the pipes for splitting, esecially the one that is out of sight under the metering head.
Note that these engines benefit from new injectors every 80k miles or so. They are not dear (c.£20 each) and a doddle to change.
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