220SEb Coupé dies after 30 mins driving

SleekLemur

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Just bought a lovely 1962 220SEb Coupé that has been in Mercedes Benz World museum for 2 years. Drove well on way home, but sputtered to a halt after 30 mins. Restarted after a few mins, but then did it again shortly after. Then did it every couple of miles. I suspected the condenser and in fact decided to change the distributor for a 123 Electronic one. Problem still exists.

Now what? Coil? Fuel tank venting? Any help gratefully received!
 

Stratman

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As soon as I read the thread title I instantly thought of fuel tank venting. I had a Daimler V8 (mk2 jag) which sputtered and misfired at 60mph on the motorway. I needed fuel and when I removed the filler cap there was a loud hissing and I could hear the tank unbuckling. The end of the vent tube (in the wheel well) was filled with mud. A little TLC and all was well.

It could also be the coil as you surmise. For testing purposes any coil of the right voltage will do, you don't need to try and find the correct one just yet.

Welcome aboard by the way. I've been to MB at Brooklands a few times but can't recall your car. Some pictures would be very welcome.
 

design guru

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I would look at the fuel pump relay, my W126 used to do exactly what you described.
 

Bellow

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As per post #2, check fuel venting first.
To check the coil, have a spare spark plug and hook it up to a plug lead and check for spark in that period between it quitting and re-starting. If you are doing this solo, try and clamp the plug with vise grips to say, an alternator bracket where its electrodes are visible to you when you crank it on the key (or use the starter solenoid in the engine bay if accessible).
 

Flyinspanner

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sounds like fuel or ignition issue.

When it stops - take off fuel filler cap - is there a whoosh of air into the tank? Maybe new tank cap required. Or vent pipe.

fuel pump relay failing once heat soaked - if you have a spare swap it.
fuel pump weak - check delivery pressure.

you have changed distributor - but maybe old ignition leads failing once heatsoaked?

heatsoaking vaporising the fuel? Check that all heatshields are in place/intact
 

Flyinspanner

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Check fuel filters are not clogged, and if it has the carburettors, that the bowls and strainers are clean.

maybe use a good spray carb cleaner after to ensure jets are not gummed nor sticky floats.
 

Stratman

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Check fuel filters are not clogged, and if it has the carburettors, that the bowls and strainers are clean.

maybe use a good spray carb cleaner after to ensure jets are not gummed nor sticky floats.
A good point. It has been sat for two years, plenty of time for residual fuel to degrade and turn into varnish. The fuel system probably needs a good clean anyway, regardless of anything else.
 

Bellow

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If the OP's description of 'drove well' is accurate, I doubt very much that the problem is carb internals. Engines do not 'drive well' on bad carbs.
If there's nothing obvious re fuel tank venting I'd go straight to spark check. If there's no spark - coil (or king lead). If there's spark investigate fuel starvation due to external fault eg, more thorough investigation of tank venting and fuel pump relay as start points. Doubt that it'd run well for 30 minutes with a choked filter.
Digging into the carbs can wait.
 

alabbasi

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, I doubt very much that the problem is carb internals. Engines do not 'drive well' on bad carbs.
Me too because the car is fuel injected. The OP seems to have a handle on what it might be, the rest of us are stabbing in the dark.

It's going to be either spark or fuel. I'm included to think fuel because once spark fails, it usually fails. I'd start by draining the tank and see what it looks like given that the car sat so long..The strainer is the drain plug and it could be blocked. If you don't have a giant hex bit, use a bolt and two nuts.
 

grober

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DID you change the coil to match the 123 distributor-these cars originally have a switched ballast resistor coil setup ----get the coil voltage wrong and will overheat and eventually fail
 
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SleekLemur

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Hi All and thanks so much for all the great replies. Much appreciated! Well, one thing I noticed this morning was that it is missing the main engine-to-body earth strap. Goodness knows how it was even running. But that wasn't the problem. Tried switching coil-to-distributor HT lead. Nope. All pipes for venting are brand new and I tried running the car with one of those emergency petrol caps, which was a loose fit. Still conked out. Mixture very rich. Black plugs and soot on driveway. leaned mixture. No sooty exhaust, but still stalls. Fuel tank was professionally cleaned and the whole system checked right through to spray pattern from the injectors (when the car was rebuilt in 2019, prior to two years in the museum). Then I decided to deliberated drive it until it completely stalls and listen for the fuel pump (yes, I know. Why didn't I do that in the first place? Sorry...) and no whine from the pump. switch ignition off and wait a minute and fuel pump whines and car drives.

I'm still a little concerned that the engine seems fine at tickover and will rev in neutral after I'm forced to pull over to the side of the road. As soon as I try to pull away though, it fluffs, but will be ok on tickover..... That's was was directing me towards the coil or condenser being the issue.

So.....assuming it is the electric fuel feed pump and this does seem a distinct possibility after two years of inactivity, what are my options ? Haven't checked for a replacement yet, but does anyone have any recommendations?

Thanks again and here's a link to some pics of "Hugo".

 
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Stratman

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It's either the fuel pump itself or, as suggested by design guru in post 3, the fuel pump relay. As the relay is about a thousand times easier to replace than the pump that's what I'd try first, but I'm a lazy so and so.

I've just had a brainwave. Get a couple of longish wires and wire a bulb or LED (with resistor) from the 12V feed on the pump itself and bring it into the cabin so you can see it when it's running. When the car conks out, if the bulb is still lit then the pump is getting 12V and so is at fault. If the bulb is not lit then it's not getting 12V so it's the relay.

Or you could just change the relay ;)
 
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SleekLemur

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Oh, Good point, Stratman. Yes. But actually, I don't even know if it has a relay! Can't seem to get a decent workshop manual.
 

Stratman

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Wiring diagram? (Another poster on that forum says it's inacurate)
W111 repair manuals (from Americashire)

According to the tiny diagram it doesn't have a fuel pump relay, it's fed directly from a fuse which has other things on it too. If they carry on working then it can't be the fuse at fault. That leaves the pump (no.38)
 
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SleekLemur

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Wiring diagram? (Another poster on that forum says it's inacurate)
W111 repair manuals (from Americashire)

According to the tiny diagram it doesn't have a fuel pump relay, it's fed directly from a fuse which has other things on it too. If they carry on working then it can't be the fuse at fault. That leaves the pump (no.38)
Thanks again, Stratman. The wiring diagram is great. I do have a manual from that link, but it's a general one for various vehicles made between 1959-1965. I found a video of how to clean the fuel pump.


Trouble is, I'm not sure if you can buy the o-ring seal for the impeller cover. Am wondering if I can switch the pump for something more modern (or is that anathema :eek:)
My previous car was a Volvo P1800 and it was a case of "yeah, stick a pair of Webers and a high lift cam on it" (Lol)
 

Stratman

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It's your car, if you want a more modern pump then go for it. Do be aware of pressures and suchlike though.
 
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SleekLemur

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I probably will go for a more modern pump. Have already gone for electronic ignition. I hope to do 3,000 miles a year of continental touring in the car, so reliability is my watchword !
 

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