Missfire W126

[420sel]

HI, I have an intermittent misfire on my W124 (4.2).

Plugs and temp sensor have been changed. Generally perfect when cold then misfires when warm or misfires when cold then fine when warm.

Mainly noticeable at idle.

Any ideas?

 

[Bert_W164]

Get it on Star.

Could be a host of things, plugs, coils, a sensor etc.

Changing bits without checking Star is like pissing in the wind.

 

[jaymanek]

Star? Its a W126.

Have you changed rotor arm and cap?

 

[ianrandom]

Is it a W126? Says W124 unless that's a mistake.

 

[markmifsud]

Even a 124 has limited diagnostics, I think just the LED blinker code on this model.

 

[grober]

Classic symptoms of migration of water vapour within the distributor body causing HT breakdown. Other possibility is an EZL ignition unit on the way out. First step is to check the state of the distributor cap and rotor arm for signs of arcing as Jay suggested and dry out the entire body with a hair drier

 

[420sel]

Thanks for all the advice. By the way it's a W126 (86 420 SEL) - a typo on my behalf. I have replace the Dizzy cap with a used one. The cap seemed to be in good condition - but you never know. I will try the hair dryer thing next.
Thanks Again.

 

[Stratman]

I believe there's a seal buried deep down the distributor shaft which is supposed to keep water vapour from the crankcase entering the distributor. This has been known to fail leading to the familiar problems.

 

[jaymanek]

Thanks for all the advice. By the way it's a W126 (86 420 SEL) - a typo on my behalf. I have replace the Dizzy cap with a used one. The cap seemed to be in good condition - but you never know. I will try the hair dryer thing next.
Thanks Again.

Bit of a false economy.. You can buy the Bosch caps and arms for less than half the MB price from Euro Crap parts..

Next on the list after that is leads... Most dont renew these and when they do they use the rubbish aftermarket ones... The only decent supplier in this country is Magencor.