Mercedes 190 misfire / non-starter

[kepla]

About 3 weeks ago my Merc 190 - perfect runner so far - started mis-firing and being difficult to start if it had not been used for a day or two. Used every day it wouldbe fine but, leave it over the weekend and it would be impossible on Monday morning. It seems to take lots of spinning on the starter and playing with the throttle to get it to fire at all, and then it is very hard to get it to 'catch' and keep running. At that point, the engine just won't give enough power to do anything other than stall untill it is nicely warmed - and then, given a few miles run, it goes faultlessly. Having been left a few days over Christmas and New Year, I now just can't get it to start at all. Fuel is present and the spark is strong. Any ideas ?

[Cockney_si]

Try checking under the distributor cap, my Honda played up recently and this was the cause, the metal bits inside had worn down.

[stanleyman]

Probably just condensation, very common this time of year. clean the ignition parts and spray with something like WD40. Could also be water in the fuel. Another possibility if you have ignition points is that the cam has worn down partially closing up the points, as it warms up expansion opens them up to run better.

[stanleyman]

Could also be a blocked jet if you have a carbureter or the choke is not working.

[PhilBy]

Before you get your hands dirty just trying spraying WD40 over the HT leads, distributor, coil etc. if it is just damp that will cure it 100%

[kepla]

Thanks for the helpfull ideas so far, guys. The car is a '93 (one of the last of the 190's) so it has fuel injection and electronic igmition. Also, the ignition HT is all protected by big rubber 'boots' against moisture. Anyway, I'll check over the dizzy cap and rotor arm and give the system a good going-over with waterproofer. Hopefully it will be something that simple. The way it is behaving, if it did have a carburettor then I would guess that the choke wasn't working right - difficult starting and no power when cold would point to insufficient enrichment I think. My worry is that something has gone wrong with the injection system - maybe something sticking - an air flap or whatever. Anyway, I'll go for the simple approach and check the ignition system first. Will post back after that. Thanks.

[stanleyman]

Actually I remember a friend had a similar problem caused by a sensor on the cold start. He used to disconnect it and it ran ok. Another friend had to have a new computer and new coils.

[kepla]

Okay, stanleyman, now you've got me worried ! How would I check for an ECU or coil problem without spending a fortune on a replacement ? The car is well worth keeping in good condition as it only has 20k on the clock despite its age (12). It didn't cost me much, though, as 12y.o. Merc 190s are commonplace and cheap. Was hoping that the famous Mercedes build quality would mean few repair bils for a while.

[kepla]

Stanleyman - I'd love to know whereabouts that cold-start sensor is located so I could try disconnecting my own. Over the weekend I was able to inspect the ignition system - all seemed to be in good order - and so over with waterproofer. Still no joy. I spun the engine on the starter for ages and, most of the time, it just wouldn't fire at all. If I held the throttle half-open and wiggled it rapidly, I was able to get it to fire a little untill I let off the starter and then it just stopped firing at all - so it still won't run. Still hoping that somebody can help me out here. Please ?

[kepla]

Time for an update:
I spent a bit of time with the errant 190E today. Took off the air cleaner and generally checked around the intake and stuff like that. Everything looked okay - clean and moving freely - so I tried starting it again. No joy after about a minute's cranking on the starter, so I checked that the fuel filler was sealing okay. The loud 'hiss' when I removed it suggested that was not the problem. Back to cranking and pumping the throttle and eventually she fired-up, after a fashion, after a long time trying. Quite happy to run at 1500 - 2000 rpm but dies if I let her idle. Engage drive and the engine just hasn't got the guts - it mis-fires like hell and dies rapidly. About five minutes cranking and pumping to get it started again and the same thing happens. I still feel no wiser about what might be wrong so I'd be really gratefull of any ideas. Thanks.