Stuttering / Misfiring (300sl)

northcave

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300sl/1992/3l
1992 300sl 12v

A little while ago (about a year) my car was starting ok and then after about 3-4 mile its would begin misfiring and stuttering under low revs. The diagnosis on this forum was an old distributor cap which can be a common problem with moisture getting in. I replaced the cap, spark plugs and leads and the problem went away. Excellent.

However... it has started again and it can't be moisture since it has been in a dry garage in Bristol and we havent had any rain for 3 weeks. I took it out the other day and had to turn back b/c it was getting bad. By the time I literally got home it cut out altogether.

Suggestions on a post card if you please ? :)

Many thanks

Tim
 

Alex Crow

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W169, W124, w202, W203, KTM 250 EXC, VW T25 camper and a Polo in a pear tree
did you replace the rotor arm as well? should have done really...
 
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northcave

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300sl/1992/3l
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Yep rotor arm, distributor cap leads and plugs.
 

television

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2002 SL500, 216 CL500, all fully loaded
2 things only fuel or spark and the spark is easiest enough to check
 

Alex Crow

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W169, W124, w202, W203, KTM 250 EXC, VW T25 camper and a Polo in a pear tree
still worth checking in there for moisture, can be from condensation.
 

rayhennig

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Your Mercedes
1991 300CE-24 Sportline
Which make rotor arm ...

My 'new' rotor arm failed after around 18 months yielding simmilar symptoms.

Was yours replaced with a genuine MB rotor arm?

RayH
 

Myros

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R107, S211, R170
I'm with ray

our 300TE did the same and it was only unused for 3 weeks. they are well fussy under that dizzy cap. and it's a pig to get off as ell.
 
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northcave

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300sl/1992/3l
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I'll get back on it and see what I find. What is funny is that the problem only begins after about 5 mins of driving which is similar to what happened last time.
 

Myros

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R107, S211, R170
that does sound

like it could be moisture building up under the cap, or that there is a crack in it. or something else of course.
The cold start injector is off really quickly, so it's not that.
 

Patm300sl

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Your Mercedes
R129 300sl m104
1992 300sl 12v

A little while ago (about a year) my car was starting ok and then after about 3-4 mile its would begin misfiring and stuttering under low revs. The diagnosis on this forum was an old distributor cap which can be a common problem with moisture getting in. I replaced the cap, spark plugs and leads and the problem went away. Excellent.

However... it has started again and it can't be moisture since it has been in a dry garage in Bristol and we havent had any rain for 3 weeks. I took it out the other day and had to turn back b/c it was getting bad. By the time I literally got home it cut out altogether.

Suggestions on a post card if you please ? :)

Many thanks

Tim
Hi. All
I have exactly the same problem with 300sl 24v new plugs , Leads, cap rotor arm and knock sensor fitted.. The Car is stored in a dry garage. This problem only happens if the car is not used for a few weeks. It start fine and after about 15 minutes idling it misfires as if it is over fuelling between 1000 and 2000, then clears, however within the next 5 minutes it will shudder to stop and not restart.
Please help
 

rayhennig

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Your Mercedes
1991 300CE-24 Sportline
Hi. All
I have exactly the same problem with 300sl 24v new plugs , Leads, cap rotor arm and knock sensor fitted.. The Car is stored in a dry garage. This problem only happens if the car is not used for a few weeks. It start fine and after about 15 minutes idling it misfires as if it is over fuelling between 1000 and 2000, then clears, however within the next 5 minutes it will shudder to stop and not restart.
Please help
I've just seen what I said 12 years ago. Did you fit top quality cap, rotor and leads? A cheapo rotor caused mine to stop when hot and restart when cold again.

Also make sure that all the suppressor caps are clipped nicely into place over the spark plugs.

Did you fit the correct non-resistor spark plugs? Mine are original MB parts, made in France by Beru. Your local MB dealer should be able to provide.

There is also a shield behind the rotor arm that many have reported can cause problems if it's cracked are allows moisture build-up and arcing. If it's never been replaced it may be worth doing.

To reiterate, it is true to say that, with these cars (M103 and M104 engines), economising on HT components is a bad idea. MB original is best, if costly. Having said that, you have a 300SL-24 so a few hundred quid on the HT system is justified for another 10 years' motoring.

On a car of this age, a new coil might not be a bad idea.

And make sure that the ignition module has a nice even, thin layer of new heatsink compound on its under side and that it's bolted down firmly on to a clean, flat (I Dremelled around the bolts to ensure complete contact) surface (the inner wing).

When you are 100% confident of your ignition system, get a multimeter that reads duty cycle and start some diagnostics (Google for help) on Pins 2 and 3 of the little round plug with the screw-on cap.

Good hunting.

RayH
 
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