BlueV

Greetings from the tip of Africa

I recently purchased a '93 190E 1.8 with 135 000km on the clock for my daily driver and am loving it. It has a few niggles that are minor and fun to sort out because of the inherent engineering of these cars.

I would appreciate some advice on the following problem though if anybody has any ideas: There is an intermittent misfire that is especially bad at idle (when it is present at all) and faintly noticeable at higher revs. Most of the time its quite drivable, but I would hate to hurt the engine and it simply drives me nuts when a car doesn't run like it should.
Any ideas where to start looking?

Thanks

kepla

Hi. We get 190's all around the world, don't we ?
I have a 1.8 too, but the coments apply to any.
A slight intermittent misfire now is likely to become worse over time so you're right in trying to investigate it before it gets much worse.
If you have opportnity or access, it could be worth having it hooked up to a diagnostic machine (computer thingy) and see what the results are.
If the car is fairly new to you, then a damn good service would probably be in order too.
There's quite a number of things which could be causing this, but I'd tend to investigate the ignition side first and then look at the fuel system. Weak or old components in the ignition system can cause odd misfiring depending on the moisture in the air and engine temp. Unless you know they are recent, new spark plugs, plug leads, distributor cap and rotor arm should be fitted. Some people will leave the ignition system alone while it 'looks okay' forever - or untill it fails them. I had my 1.8 refuse to start early on this year and a change of plug leads and distributor cap transformed it. The old ones looked fine, but had probably been there for 6 or 7 years, maybe longer.
Once you know the sparks are spot-on then investigate the fuel/air system for dirt and gummed-up parts, but I'd suggest you fix the sparks first and see how the car behaves.
Let us know the result.

BlueV

Thanks Kepla
You are so right -starting off with a comprehensive sevice is a must. I have covered the basics fairly well but will tackle the ignition system next and let you know -holding thumbs.

DarkCreep

It wouldn't hurt to change the spark plugs either .

I know when I clean my engine and water leaks on to my spark plugs, my engine misfires like crazy. After a while it goes away though.

kepla

Yes, DarkCreep, I would agree with that. I would consider a chnage of spark plugs, and also things like the fuel filter, to be part of a 'major service'. Whenever I get a car new to me (maybe once every ten years or so) I go right through it changing everything that would be done at the manufacturer's highest level of service. This will included ALL filters and ALL fluids and any forms of drivebelts etc. I also inspect all safety items like the braking system, changing the friction pads and shoes, and inspecting brake discs and drums. I also take apart adjustable bearings, such as wheel bearings, clean, re-pack with fresh grease and adjust them properly.
I'm not saying that all these things are done 'instantly' - they'll get done progressively over a period of weeks. I won't usually drive a car on trips of more than a few dozen miles untill I am satisfied that all these basics are okay. By the time I am done I have got to know the car pretty well throughout and feel more confident that there'll be no hidden surprises !
If you get some serious mis-firing from a little moisture on the engine then I'd suggest that you've got something amiss. Remember motorbikes aren't really much different in technology to cars and yet they run quite happily in the rain. Spark plugs themselves are inherently waterproof as they are sealed gainst combustion chamber pressures. If I were you I'd investigate the plug leads. You wouldn't want a bit of air-bourne moisture one winter's morning becoming condensation and preventing your car from starting, would you ?

BlueV

Thanks for the advice guys. It turns out that the problem appears to have been ignition related and while it is not entirely cured yet, a huge improvement was made by just replacing dodgy suppresors. (its a first for me to make up HT leads- I was used to them being complete ex-factory)
The plugs were thrown out with the engine oil and all filters the day I picked her up, but I should have taken more time inspecting the leads - there were signs if I took the time to notice them.
Anyway, the engine now runs smoothly when cold and does not cut out anymore at idle when hot, but it still idles slightly rough when hot. I am picking up new dist. cap and rotor over the weekend and hopefully this will sort out the remaining roughness.

kepla

Hi, BlueV - glad to hear that you're on the right track and have got an improvement already.
One thing I'll point out, because that's what was up with my car when I got it.
Aside from the length, thread and heat range there's one other thing you have a choice in with spark plugs - you can get them in supressed or non-suppressed varieties. You probably know this already.
You can also get spark plug lead suppressed or non-suppressed. The non-suppressed ones use copper cores and plain ends. The suppressed ones might use carbon cores (yuck !) or suppressed ends or whatever. You probably already knew this too.
When I got my 190E and it started failing to start easily I eventually realised that it had been fitted with both supressed spark plugs AND suppressed plug leads ! You can probably imagine what that did to the sparks. All it took was one nice damp winter's day and the 190E became 'purely ornamental' for a while !
I now run unsuppressed plug leads. The set I got are completely moulded-over in rubber and look like they are sufficiently water-proof to use on a motor-bike. I try not to let anything let me down more than once !