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280SE woes

Started by entresz, 27 May 2021, 07:58 PM


Hi everyone Trevor from Tenterfield NSW Australia here, been given a 1974 Mercedes Benz 280se for free as it was destined to be crushed or sent to the wreckers, car is complete and running but unfortunately only on five cylinders not six, did the usual easy things first, changed spark plugs and leads for new ones, still misfiring, next checked fuel injectors all working, about to check compression on all cylinders, any ideas where to look next. Another issue i have is where to find a workshop manual as i can't seem to find one. I have other classic cars so i can work on mechanical stuff but this merc is more complex than my 1960's Ford Zephr's.


Hi Trevor. The distributor cap should be the next in the list to check. Its rotor too but I doubt the problem is coming from it. Very easy to check cap's interior. Look at each contact. You can clean them too. Check for presence of moisture, corrosion. If that's the root cause, they are still available at decent prices. I hope not, but if all electrical components check ok, then the misfiring could be coming from a fuel related issue (e.g. fuel distributor membranes, a sticky plunger, etc).
Have you determined which cylinder isn't firing?
W116 1977 280SEL & 1979 280SE
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The handbooks are all in the technical section of the site.

W116 1977 280SEL & 1979 280SE
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HI all, i located the misfiring cylinder by removing each spark plug lead whilst car was running, (one at a time) if the car ran worse then that cylinder is fine, if no change that cylinder is not firing, turns out it is number 3. Today i intend to put a small amount of oil into number 3 and see if the compression changes ie if compression increases that would indicate rings are bad, if no change it would indicate valves are bad. One would hope it is only a sticky valve. Thanks for the link to a workshop manual as there are wires in the engine bay that i have no idea what they do. Here are some things i have learnt about this merc, they are a big car (one metre longer than my Mk2 Zephyr), i thought all mercs came with leather interior, not so apparently only top end ones did but you could upgrade. They are a solid car but quite heavy so getting good fuel consumption is not going to be like my 2011 Subaru Outback which uses about 7 litres per 100 kilometers  (not sure what that is in mpg). I have been told by a member of our classic car club (who owns a 1979 merc) that there is a Mercedes Benz specialist in a town approximately two hours drive away but will give advice over the phone so maybe thats good to know.


Trevor from tenterfield Australia  here, just letting everyone know i did the compression test on my 74 280se number 3 cylinder  (the one that is the cause of the misfire) had good compression so removed the spark plug and squirted some oil into the cylinder no change to the compression thus i figure it's valves. More work ahead.


The hickups on high way might be the alternator. I had the same thing in my 1973 R107. Suddenly the alternator gave up and I had to put another one in. No hickups since then. D-jet must have full power from the alternator. 
350SL 1973
350SE 1975
SL500 1996


Its been a while, but I finally followed up & got round to following some of the tips from UTn_boy from last years post, around June. (Thanks UTn_boy)

Finally purchased a new set of leads and a new Bosch coil.
The old leads I replaced were Beru brand and I got a "shock" from touching 2 out of the 6 leads. Obviously they had to go. Couldn't find a Beru distributor downunder, or perhaps I was looking in the wrong places. Found a company interstate (Sydney) that manufacture auto ignition leads "to order" in Oz, so I purchased a set from them.
I figured new leads of any calibre must be better than the bad ones I had on. They seem decent quality. Time will tell.

Changed the coil because it made sense. I will store the old working one as a backup.

I will do some K's over the next few days and see if there is any discernible difference. 

As for the question I was asked but never answered "There are a  lots of cranks before that when hot or cold, or both?"  The answer is "Cold"

& are the ballast resistors readily available? I havent looked yet.



I ended up with Karlyn ignition leads as I couldn't find Beru either. So far so good, only issue is that the leads have 90° ends where they go into the distributor cap, the originals are straight, so the black plastic cover doesn't fit haha!!

I would try the old resistors you have, only takes a few minutes to change.

I recently changed my ignition system to electronic (as well as new leads/plugs/coil/distributor cap/rotor). It worked great for a while then slowly started to misfire when hot. When cold it was fine. Got to the point where as soon as it got to operating temp it wouldn't hold idle and had no power. Turns out the electronic ignition failed, the coil seemed to have an issue too. Only lasted 1400km, put the old coil and points back in and it is driving great with no misfires now.
1975 280S - Australian delivered


Quote from: mrkozzy on 26 December 2021, 11:34 PM
Are the ballast resistors readily available? I havent looked yet.

Yes, a sof last year at least. Both from Mercedes and aftermarket directly from Beru. The part that comes from Mercedes is the exact same part.
1993 "Pearl Blue" W124 280TE
1988 "Arctic White" W124 200T
1979 "Icon Gold" W116 450SE