1986 SL RUNNING LUMPY

[alan a]

1983 300SL running lumpy,, plugs and leads fine new Distributor cap fitted ,starts up fine, HELP PLEASE

 

[Dizz]

1983 300SL running lumpy,, plugs and leads fine new Distributor cap fitted ,starts up fine, HELP PLEASE

Air leak due to a split pipe perhaps?


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[grober]

If its the first of the M103 engined cars they are prone to cylinder head gasket problems at high mileage. [ check for wet/oiled spark plugs] The distributors are also prone to internal condensation problems where water condenses in the body of the distributor when cold but as the engine warms up the water vapourises and moves to inside the cap causing internal shorting and engine misfire. solved with the judicous application off a hair drier to dry every thing out. Its also advised to use pukka MB dizzy caps and rotor arms as cheaper pattern parts often fail quickly in use

 

[Dodipops]

Fuel metering units can also tend to fail later on in life.

 

[optimusprime]

Check all fuses and earth points -remove the learth cables and clean up the body,, then grease ,,and refit . Also vacuum leaks ,look for hose damage on the rubber conectors .

 

[alabbasi]

I'll add low tire pressure to all of the above.

Jokes aside, you're not giving much by way of details. You should read up on both the M103 engines and CIS fuel injection. The system is prone to several issue that can cause lumpy idle from minor issues such as vacuum leaks to major ones like fuel lines gumming up due to sitting or head gasket problems. I'd start by doing a bit of reading and then tackle the simple tasks.

Thanks

 

[alan a]

If its the first of the M103 engined cars they are prone to cylinder head gasket problems at high mileage. [ check for wet/oiled spark plugs] The distributors are also prone to internal condensation problems where water condenses in the body of the distributor when cold but as the engine warms up the water vapourises and moves to inside the cap causing internal shorting and engine misfire. solved with the judicous application off a hair drier to dry every thing out. Its also advised to use pukka MB dizzy caps and rotor arms as cheaper pattern parts often fail quickly in use

thanks for advice but how often do you have to use hair dryer. i get my parts from The S L Shop

 

[alan a]

I'll add low tire pressure to all of the above.

Jokes aside, you're not giving much by way of details. You should read up on both the M103 engines and CIS fuel injection. The system is prone to several issue that can cause lumpy idle from minor issues such as vacuum leaks to major ones like fuel lines gumming up due to sitting or head gasket problems. I'd start by doing a bit of reading and then tackle the simple tasks.

Thanks

it seems ok when cold but as engine warms up it starts to run lumpy

 

[alan a]

thanks for advice but how often do you have to use hair dryer. i get my parts from The S L Shop

also it seems ok cold but when it gets hot after a while it seems to start running lumpy but not all the time, its so frustrating

 

[grober]

thanks for advice but how often do you have to use hair dryer. i get my parts from The S L Shop

You should only need to do this very occasionally- maybe once a year if that- provided everything is dried out.There's a shield and o ring seal below the rotor arm take them out and give everything a good clean./ dry out- if suspect renew - always use MB HT parts
https://www.startekinfo.com/StarTek/outside/12264/Program/Engine/103/15-3010.pdf

Other possibility is that your EZL electronic ignition unit is overheating- the heatsink material between it and the inner wing dries out and it overheats causing a misfire- unfortunately by the time this happens the unit is usually damaged and has to be replaced.
Mercedes-Benz Model 124 Servive Manual Library

 

[alan a]

Thanks mate

 

[alabbasi]

Bad coil could cause this, as would the insulator that sits behind the ignition rotor.