560SEC: Sudden loss of power, and misfiring
 

My SEC has been running perfectly until yesterday morning...I started it up, and it was running fine until about 5 mins into my drive I stopped at a light and made a U turn, and all of the sudden the engine started misfiring and shaking, the idle dropped to a little below 500RPM, and when I press the throttle, the car bucks and jerks and will barely accelerate. It seems like the farther I push the throttle down, the more the car slows. The engine sounds like it's trying, but the car doesn't really move.

My first thought was that it could be a vacuum leak, since I have had that problem in the past, but when I start the car, it runs fine for about 2 minutes, then the idle drops and it starts misfiring... any ideas? I ran it by my local benz specialist, and he basically just gave me a blank stare. Any help would be appreciated, since the car isn't driveable like this, and it's my daily driver...Thanks!

Is it smoking???

I had something happen similar, though not that extreme, with the SL. Turned out to be the fuel distributer was clogged up.

How old are the Fuel Filters?

I have no idea how old they are...did you have to replace the fuel distributor? How did you determine that was the problem?

What throws me on this problem, is that it runs perfect right after startup, then it starts acting weird after a short while. Runs perfect for longer when cold, when the engine is warm, it will run ok, then within a minute or two it will start bogging down and idling roughly. I noticed my fuel pump is buzzing and sounds kinda sickly...I'm going to take it back to the benz specialist and have him check the fuel system control pressure.

primary electrical
 

Misfiring all of a sudden, is usualy an electical issue, have you checked the coil and coil wire and the distributor cap and rotor for cracks, also the fuel pump buzzing sound is normal.

Ben

The day before it started acting like this, I had electrical work done to remove the defunct aftermarket alarm system that was just a mess of wiring under the passenger floormat. Is there anything down there that would affect the engine?

Darn, I was hoping somebody would have responded by now...I guess the car will just have to wait until I get back from my two week trip to Oregon to be fixed. :(

I'm with Ben on this one. Your description sounds like bad wires. Could also be what is mentioned above. Same idea. Also possible crank sensor, and technically could be a lot of things, but I would start with wires. Ohm out the wires with an ohm meter.

Where is the coil located?

There is a wire in the middle of the dist cap. On the other end of the wire is the coil. Ohm the wires first. If they are resistor wires then they will read some K ohms. A bad one will read Meg ohms or infinite.

I just replaced the spark plugs and wires. :)

I see that you used to own a Toyota Supra...did it ever blow it's head gasket? hehehe :D

I had exactly the same experience with my 83 380 sel. It was running perfectly, then I stopped at a light and when I gave it the gas it didn't want to go. Much reduced power, and bad misfiring. I was about 30 miles from home and the longer I drove it the worst it got. By the time I got down to the last 9 miles it was barely running, and the more gas I gave it the worst it ran. I was on the highway and couldn't get it up to 40 mph. The last clue was a strong smell of fuel.

I took it to my indie. he took one look and one smell said, "ignition coil." He had a good used one sitting on the bench, popped it on and the car ran perfectly. I bought a new coil (original Bosch - $65) and for good measure a new ignition control module (aftermarket Huco from Germany - $65) and haven't had any more problems.

those aftermarket alarm systems often cut a wire completely and run one end one way etc.it seems like a massive coincidence that the problem started the day after removal.i gave up believing in coincidences 30yrs ago.

I just got a call back from the mechanic...he said both fuel pumps are tired. They are making a lot of noise, and the fuel pressure drops by almost 40psi when the misfiring occurs. Repair estimate $750. O_O

At least he figured out the issue. Whats bad is trying to chase down problems that nothing seems to fix.

Of course! And it had bad wires too! The suspension on that thing was bullet-proof though. Handled great.