oh oh i think did something wrong
 

hello everyone im a new member, ive always owned a Mercedes, 300ce models only, but yesterday bought a 1999 ML 430. like an idiot i washed the engine bay as it was really disgusting, when i re started it runs very rough and check engine light came on, please help this old fool figure out what i can do, im totally lost on these newer models

Get it scanned. It's probably a misfire--you probably got water in a spark plug hole or something. At any rate, we don't know what the code is until you get it scanned. I've always ever washed my engine bay with the engine running and only with a garden hose and simple green or purple power on things like vacuum lines, electrical wires, the like. I'll use a pressure washer if I'm underneath cleaning the transmission, oil pan, or suspension or whatever, that has no wiring or hoses, but yeah, its probably just a little water that got in somewhere it shouldn't be.

I agree let engine run while cleaning. Hopefully it is something minor where water got in

Thank you very much will do in future, hope the scan comes back clean.

I really wouldn't use water to wash new engine compartments using a hose or pressure washer, spray bottle yes but careful. But if you do use high volume water let it sit for 2 or more days in hopefully warm weather to let it dry out before trying to start it. Yeah laugh but it needs to be dry, as you have discovered, and by not being dry something got goofed up. Oh and disconnecting the battery before H2o washing maybe a good idea as well. Even electronic circuit boards can be washed but not electrically activated when wet.

In all probability the eng. has multiple misfires and running the eng. will cause serious harm. Water has collected between the spark plugs and the spark plug wires.

Again thank you for your in put,i dont think ill wash the engine in a newer Mercedes ever.ill keep to the older ones like me

The ignition coils seem to have their plastic coating crack with age, which then makes them susceptible to water and rust, which seems to be able to ruin them at times. When you lose one to this damage the truck will run extremely bad.

If it's just missing a little bit you probably knocked off a vacuum line, got some water in a sensor, or water in the spark plug holes. When it's one of those problems it will usually resolve itself on it's own in my experience.

I had a 93 w124 3 liter I could pressure wash the engine bay till kingdom come, but I had 91 w201 with the 2.6 where if you pressured washed the bay it would kill the car and not allow it to start for hours. Could never figure it out. All my other MB have loved pressure washing but I always stay away from the coil packs.

Try blowing it with air, leaving the hood open in sun, etc. Unplugging, inspecting and unplugging some connectors. And or looking for vacuum lines damaged or unplugged.

The check engine light may remain on until you clear it with a code reader or battery disconnect.

Thank you, replaced all the plugs, i was going to anyway, found cylinder 7/8 default coil so i have one on order, ill check all connectors, and check vacuum lines,seems that at one point there was a mouse living in the engine bay chewing plastic. so ill give a very good once over.
and yes 124 i believe were the best Mercedes ever built, im always looking for a 300ce my favourite

good afternoon everyone, well still having the same misfire, changed coil , checked everything i can think off but still, same code cylinder 7/8, anybody have the same experience before im at a loss atm,

coils or wiring?
swap one of the other wires to test.

And this all started with the washing?

How bad does it run? Like does it run like one or even two cylinders aren't firing at all...basically undrivable, Or just a little off?

Ya that idea to unplug or swap the coil/wires/plugs around and see if what changes is a good one. Maybe more than one coil failed.

You can also stick one end of a screwdriver on a fuel injector and the other up to your ear, you should hear the clicking of the injector.

For some reason I seem to remember the 7/8 misfire may be related to the EGR valve. I'd check the vacuum lines there at the back of the engine. There's at least one really hidden underneath that tends to break.

How bad are the engine mounts? I've heard on these engines if the engine mounts are really bad for a really long time they've been known to damage the wiring harness.

I'd also just Google or look on YouTube for diagnosing that code or just 7/8 misfire or misfire in general.

I'm not sure if the w163 has what they refer to as electron misfire detection (or something with electron) and figuring out how that all works and if it has it may help you determine how to diagnose.

But after writing all that I still think the most likely event is you just had more than one coil failure.

Could also be a malfunctioning crank or cam sensor. Check grounds. Maybe even MAF sensor.

Good luck!

Again thank you , waiting now for a friend to stop by with his machine to diagnose again.but ATM ill try all that you mentioned and probably more lol. i hope to get it running smooth again soon. thank you again for every bodies suggestions and know how on for me this modern Mercedes. i will up date soon

Just wanted to say check the connections on your fuses and relays, etc for oxidation etc. Sometimes they go intermittent.

thank you very much
 

Sorry been awhile i have been a little preoccupied lately, but to update everybody who gave me the advice , yes it was the coil, now running perfect. now a few niggley things but i will get around to it eventually. then i might even go for a long run before the snow hits.thanks again everyone