Hi,

Recently purchased a '97 CLK 320. The car already had quite a bit of electronic issues ( BAS/ESP light comes up, dashboard lights are busted I think, and some random things every now and then ).
I left the car home while I was on holiday, and when I came back 3 days ago, it couldn't turn on anymore. Some random info on the issue:

- I lose fuel everytime I top up, so my guess is maybe humidity went into the tank and somehow messed with the fuel filter or fuel pump ? But it's been quite hot and dry recently here
- There's air coming out of the exhaust. It sounds like gas isn't being sent into the engine.
- I'm not sure that I hear the fuel pump turning on when I turn the car on.
- Battery is fine, car keys batteries are fine as well.
- Electronics are really weird on this car, sometimes the lock/unlock won't work properly, until I unplug the battery for 10min and plug it back.
- There's a relay that is.. weird I think, I'm not sure if I'm testing them correctly or not. This one 0025420319 I think, when I test it it gives a reading like "1.1 M Ohms", while all the other ones give me about 80 Ohms or "Auto" ( I have an automatic multimeter, some of the readings only show "Auto" when I test the 30/87 pins from the relays or when I test 85/86 ).
- It might be the fuel pump, but I have an invoice from the previous owner for a fuel pump in August 2024. Not sure if the change was made though, it's only an invoice for the part itself, the previous owner's brother was a mechanics, but when I took it to the garage a couple months ago he told me previous work on the car was pretty badly done, so I'm not sure if the fuel pump was actually changed. But why would he order a fuel pump and not change it ?

What could it be ? Some people mentioned the fuel pump, but why would it break right in the 2 weeks I wasn't home ? Same for the crankshaft position sensor, why now ?
And with all the electronics issues I've had, I have a tendency to say it's electronic related. Is there a way to test the fuel pump and the crankshaft position sensor ?
What else could it be ?

Thanks

 

Remove a spark plug. Does it smell like gas?

There is one answer.

Borrow or rent a fuel pressure gauge for a more accurate answer.

All those electric issues sound like water got in at some point. Did it? Any mildewy smells inside or in trunk? Do windows fog INSIDE after rain?

 

Sorry for the late answer.
Removing a spark plug kind of goes above my very limited set of skills haha, I will if there's more evidence that it's coming from there though

I tested all the relays I could find, and the green one under the hood ( that allegedly controls the engine ) is busted. It doesn't click and the readings with the multimeter seem to validate that. I ordered a new one and i'll swap it. There's another one ( the black one that is right next to the green one, between the green one and the front of the car ) that clicks, but multimeter seems to show it's not doing its work and it's always open, so I ordered a new one as well.

I have another issue though ( that I did have when I came back home but somehow I forgot about it ). When I switch the ignition on, the dashboard lights up, but not all the lights that usually come up and then turn off when the car is ready to be started. And when I turn the key to turn on the car it doesn't do anything. When I switch the ignition off there's a small noise that I can hear sometimes, but that's about it. Only the dashboard ( odometer, clock.. ) lights up, all the starting up lights never light up.
Does that help the diagnosis ?

There's no smell in the car apart from the smell from old mercedes, there's no fog or anything ( but it's really warm here these days ). When I bought it I did remove a lot of leaves and dirt from between the bottom of the windshield and the hood. Like really a lot. I wouldn't be surprised if water got trapped there or somewhere close at some point.

 

I heard about the K40 relay that can go wrong at some point in the life of those cars.
i pulled what i think is the K40 relay box ?
The solders look fine in my very unexperienced opinion, but the there seems to be blue/whiteish stuff on the circuits. Also 2 fuses have that sort of thing on one of the branches.

Is that the K40 box ? How to I remove the blue ( corrosion ? ) on the circuits ? Do I have to unsolder and resolder the circuit ?

https://imgur.com/a/yBAkll5

 

Watch this video for help cleaning.
John

 

Thanks, definitely helps, I bought some circuit cleaner and it helped with the fuses and some of the circuit, but there's still more corrosion that is really thick and won't bulge. I bought some IPA which apparently helps more than circuit cleaner, I'll let the circuit soak in it a bit, maybe ?

 

Try vinegar

 

Thanks, but unfortunately still nothing. I replaced the 2 bad relays, replaced all the fuses, and cleaned the board with vinegar, then rinsed with IPA ( there's still a decent amount of corrosion, but I think I got rid of some ), let it dry, same symptoms.
Relays ( driver side, under the hood ) could have been the cause ( though they're apparently not ), but why would the corrosion from the K40 module suddenly cause issues.

What else could it be ?

 

Anyplace things connect it HAS to be shiny metal to shiny metal. If there is white, green, or grey/black stuff between metal, they don’t make contact.

 

Got it, I'll try to soak in in IPA or completely replace it then.
But out of curiosity, how did it work for so long with that corrosion and why did it suddenly stop working ?

 

Who knows. But I’m not saying this for sure is your problem.

But corrosion is always bad. Electricity through a board that is wet causes electrons to move the ions present. You effectively electroplate things to another place where they short a pin or transistor.

If you opened a laptop or desktop computer with corrosion inside, would you expect it to work correctly? It’s especially bad with small ICs with tiny little pins next to each other.

 

Okay so I've changed the K40 module, and I have the exact same problem.
So:
- Odometer/clock shows, signals work, lock/unlock works, steering wheel does unlock when I turn the key
- No lights ( battery, engine, ABS/ESP etc.. ) on the dashboard
- Battery is at 12.7V when plugged in, 12.5V when ignition on
- I tested 2 fuses that are 60A, my multimeter shows 0 Ohm and beeps, apparently it's a good thing ?
- I changed a couple relays that I suspected could be broken

Really lost right now..

 

That corrosion looks terrible, I zoomed in and looked. What is really bad is if it connects two pieces that are next to each other.

The worst thing for electronics is when power runs through while wet.

Good news is you figured out “continuity” function of your voltmeter. 0 Ohms is indeed “these points are connected in a dead short”, which is good when they are meant to be. Like a fuse.

The beep is nice because you don’t need to look at the meter, you can just hear it. When testing fuses always try to test from connector, not just the fuse itself.

conversely, if you see two things near each other that are only connected by green or white crusties, and the meter says they have continuity when they shouldn’t you know to clean the bridge of corrosion until the meter says they aren’t connected anymore.

You have water intrusion issues. You will need to clean and sort that.

If carpet is wet anywhere, look under it. If a SAM got wet you will probably have to replace it. Keep hunting.