Colder Weather Cold Starting Problem

[Scott_F]

My W124 220CE (M111 engine) can give problems starting in colder weather.

It is garaged and can be unused for a couple of weeks at a time. Last winter it often wouldn't start from cold straightaway. The engine turned over but it wouldn't fire. I tried not touching the accelerator and also slightly and fully depressing it but to no effect. If I left it for 5 minutes and came back it started on the button. It was less of a problem if the car was used regularly but was it never guaranteed to start straightaway.

Over the summer it has given no such problems but now that the temperatures are dropping it has started to revert to type.

Does anyone have any suggestions as to why ?

 

[jefrs]

Starting and then running fall into two categories: fuel and electrics.

I've not had any problems with modern motors but used to have fun with old ones particularly won't-go won't-go Fords and British m/cycles. The main diagnostic is the state of a spark plug: you only need to look at one of them.

Rule of thumb - dot and daw: if an engine stops by dotting out, makes a "dot" noise and stops suddenly then it's electrics; if it daws out, makes a slow "daw" noise and splutters to a stop then it's fuel. Not a hard and fast rule but can help when an engine tries to start but won't run.

If the engine can turn over on the starter then you are not short of electrics but may be short of sparks. Check a spark plug for condition and any sign of condensation. If your sparks are good then its fuel. An engine should start even with really bad ignition timing, provided it is getting a good spark. A set of fouled plugs won't start an engine: find cause of fouling.

Are you getting fuel to the cylinders? Smell the exhaust and the spark plug you took out. Fuel can drain back when the engine is not used. Find cause of lack: pump; blocked filter; float bowl valve; etc; wrong mixture.

If water vapour is getting into the cylinders then condensation can short the plugs out. Note that water is a natural combustion product. Oil on plug is a bad sign.

Doesn't help much, you probably need one of them new-fangled computerised mechanic thingies operated by a spanner-monkey.