I have a 1985 560SEL that won't start after it rains. It will crank over but won't fire. After a couple of days after the rain it will start. The distributer cap and rotor have been changed. There is not visible water in the engine compartment.

Any ideas as to what it might be?

Thanks,
Josh

Josh,

I'm not an expert, but I've read a few posts from them regarding this problem, and it seems that when moisture plays a part in the car stalling, the problem is most likely electrical in nature, as opposed to a fuel delivery or vacuum leak type of problem.

I had a similar issue with my '87 300e. It would generally start up rather quickly, but had a bit of a stumbly idle, and just after warming up, was prone to stalling at low speeds. It would choke a few times, and die. This problem was more pronounced after a long rain, but mine would usually start later that day when it had dried up a bit, never did I have to wait a couple days! A couple times I darn near wore out the starter to get it to start, and babied it out of town (light gas pedal pushin' until it got up to speed). Once I got it on the highway, it was fine.

Anyway, I took it to an independent Benz mechanic who replaced a laundry list of things to fix this, distributor cap, rotor, ignition coil, new spark plugs and spark plug wires, OVP relay, O2 sensor, wiper blade, and after he was done, I still have a bit of a stumbly idle, but it hasn't stalled, and that was a couple weeks ago. I think it was the wiper blade...

Do you live in a perpetually damp part of the globe? Pacific Northwest, perhaps? When trying to start does it catch and then die, or does it just not catch at all when it's wet? If it does ever catch and die, how does it die? Does it go out fighting with a few chugs and some engine rocking, or does it just cut out, like someone flipped switch? You mentioned the distributor cap & rotor were changed, so I might think the coil maybe needed to be changed, too.

Good Luck,
Oak

I just checked the coil and it seems fine. I am getting spark to the distibuter. I may replace it just in case. I was wondering about the CPS.

Josh

When the car will start take a look under the hood at night, (when it's dark).
Start it and watch for sparks around and along the plug wires, the wires could be the problem. Since you have spark from the coil check things from there.

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1986 300e 392,000+ miles
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When you checked the coil for spark, were you checking during the "moist" conditions or under dry conditions?

I would still bet it's the coil.

My VW had this problem many years ago during moist weather, and when I pulled the coil wire to check for spark, blue crystals disentigrated from the coil input...corrosion, no doubt. Cleaned the coil and all was well (although I went ahead and replaced it a little later anyway)...

__________________
2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car

Next time condition exist, spray the plug wires and coil connections with WD40 and wait 5 min.... Retry.. if it starts , replace the plug wires................

I had this problem before. Turns out the drains to the electrical centers were clogged with leaves. When it rained, water actually pooled under the fuse box and by the battery so all my cable s were under water. So I cleaned everything out and the problem went away. Now I regularly vacuum these areas during fall and spring.

If you are experiencing corrosion/moisture at the ignition wire connections, it would be wise to water proof the connections by applying them with the gel that comes with new wires. I forgot what they're called.