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.

Can anyone tell me where the fuel pump relay is located on my SEC?

Are there any special tools needed to replace both fuel pumps?

On my 500 SEC, it was in the rear of the fuse box.
The big relay that is NOT labeled 'klima'.

In your car it's near the center of the car between the firewalls between the ABS brain and the Klima relay. It'll have Kickdown or the like on it. Maybe 6000RPM min too. Black 1" X2 1/2" by 3" tall approx.

Ok, I replaced the fuel pumps, and am using a known good Fuel pump relay, and it is still doing the same thing!!! :mad: Looks like the mechanic's diagnosis was wrong. UGHHHH!!!!! I did, however replace the OVP with a spare I grabbed at the junkyard, and it made it run quite a bit better, almost driveable, but still not quite "right". There is still a slight loss of power, but when you mash the throttle it takes off like nothing is wrong. I should also mention that it runs perfect, smooth and responsive for about 30 seconds to a minute, then it starts to bog down and run badly.

I had a similar problem and I found it was a cascading effect... I had bad ignition wires that threw off everything I replaced cap, rotor, wires, plugs, and coil, ground wire, and cleaned out the idle air control valve... if you have never done these things it's about time you do and it's not a loss even if this is not the cause. maybe your cold start valve is stuck open... look it's something simple... hopefully

Well the car is back at the mechanic's shop...let's see what he comes up with next! :rolleyes:

Warmup regulator!!!! May be the culprit. The 30 seconds thing sounds like the WUR or the Cold Start injector. The gasket under the Cold start injector my be toast causing it to suck air. How about vacuum lines? Is the EGR hooked up correctly? does the Tempo Vac Valve work? Lots of thing screw up the Idle. If the EGR is actuating at idle it'll run like crap, almost die.

Wife's Maxima had symptoms nearly identical to what you described, particularly the parts about it (1) starting fine and idling fine for a bit and (2) bogging down on accleration. Injectors were replaced, CTS replaced and plugs, wires, distributor/rotor and coil checked out good. Turned out to be MAF sensor.

On mine, a 1987 560SEC, the fuel pump relay is right below the windshield in the middle of the engine compartment.

Got a call back from the mechanic, he replaced the fuel filter, and all is well. Apparently it was clogged to the point where it would no longer flow. He even gave me a demonstration with compressed air, and the filter would barely flow, and lots of dirt and chunks came out of it.

Change your fuel filters people!! :)

fuel flow
 

Did your mech offer any relief for faults misdiagnosed and work/parts done but not needed?

Seems that fuel filter would be the logical place to start rather than last resort.
----------------------------------------
BTW, a similar temperature related effect on my 560SL (basically the same engine and control system) was isolated to the engine temperature sensor that inputs to the EZL. Ran good cold then went sour when warmed up.

Well, know he has the peace of mind, knowing that all of those parts have been replaced and are not likely to break anytime soon . . . .

Nope, he even charged me more than he had originally said he would. I ended up paying about $100 for the filter change.

Is it finally running correctly? My US spec 380SE's CSV (Cold start valve) is inop but doesn't hamper the performance, except on start up (you have to give it a bit of gas). Hopefully it's fixed but it does sound like a faulty FD. The same thing happed in my 200TQ just pulling out of the driveway and driving up a hill and all of a sudden no power... Smelled raw fuel and car bucked like a horse...

Makes you wonder how clean that fuel is coming out of the pumps! :eek:

All mechanics serve a need - but the fuels of today are not being addressed properly.

I clean tanks of all types and it will overwhelm you with the crap that circulates within our tanks. This applies to both diesel & ethanol gas. As responsible car owners we need to practice "predicitive maintenance". This is where we forecast what the problem before it happens.

Good Luck,

Luther Carrier

what type of ignition wires and sparkplugs are being installed .
mak