1988 560 SL: Start After A Long Nap
 

Bought the above car out of an estate, 38,000 miles which various indicators say is likely correct. I know the car has sat inside a garage for years; not certain how many. It did not have bad gas in the tank when I drained it. New fuel pumps and filter, new engine oil and filter, new transmission fluid and filter; new coolant; new belts, hoses, thermostat, spark plugs, power steering filter and fluid. I replaced the four brake hoses; replaced the rear muffler and all the exhaust hangers; new battery. Now when the key is turned on, the fuel pumps come on, but with very active (normal) cranking, no running. I suspect there is no spark. I admit I gave it a shot of fuel in the fuel injection intake, no reaction. I have examined the ignition rotor and cleaned the terminals. Please advise. I have some other maintenance items planned, but it is much easier if the car will move under its own power of course.

Are you getting spark at the coil wire? Might be timing problem. With #1 cylinder at TDC the rotor tip should be pointing at the scribe mark on the rim of the distributor which you will see with cap removed.

Does it have spark or not? That's the first question.

Duke

No spark. Before I got the new fuel pumps, i gave it a shot of gas in the intake and it hit as if it had spark. Now that I have two new fuel pumps (they run at the correct time), nothing.
I did loosen the dist cap once to get a bolt out; I also removed the dist rotor and cleaned the contact on the arm end.

If it had spark I would suggest the fuel accumulator.

I don't know the details of your 560's ignition. My 190E 2.6 has a "black box" called the EZL and a TDC sensor that indicates TDC of each cylinder when three notches on the flywheel pass by. Initial timing is fixed by the EZL and the distributor only distributes secondary voltage to the six cylinders.

The system appears to be quite reliable, and I don't even want to think about what a new EZL would cost assuming they are available. The most common failure is usually the crank position sensor. I think dealers had a special test set to check the system out.

Hopefully someone familiar with the 560's ignition system will be able to help out. In the meantime remove and inspect all the electrical connectors on both the primary and secondary side. In my experience one of the biggest issues on vintage cars is electrical connectors. Over time even if well cared for they can develop high resistance due to even minor corrosion and cause all kinds of flaky problems.

Duke

Randy, you didn't mention replacing the coil. I would expect the entire fuel system to have gunk inside if the vehicle sat for an extended time. Try blowing air through the fuel line from the fuel pump location to the engine compartment. Check the condition of the fuel injectors, etc.

560 SL UPDATE
 

Ignition is firing; at least it triggers my inductive timing light.

Update: I loosened the fuel inlet to the fuel cooler, driver’s side of the engine compartment. It wasn’t dry; about a tablespoon of clean fuel dripped out but it wasn’t under pressure. I connected clear vinyl tubing here and directed it to a container. When I turned the key on I could hear the pumps come on and run about 1 second then stop. No fuel came out of the connection.
Next I plan to loosen what I have identified is the other end of this fuel
Line, and blow through it with compressed air.
I also see a device just ahead and above the fuel filter (new filter, by the way); a device which looks like it could have a diaphragm: maybe a fuel pressure regulator?

Update: Got the engine started! It's amazing how much better it goes when it has GAS IN THE TANK...

Now I have to get rid of the classic 1500 rpm idle...

Randy, glad to hear you got the engine running.

That sounds like the fuel accumulator. It failed on my 190E 2.6 a few years ago. I started a couple of threads one of which was a destructive analysis report that revealed cracks in the diaphragm that allowed fuel to short back to the fuel fed hose from the tank resulting in no fuel pressure buildup.

The symptoms were intermittent hard starting (long cranking time) that got progressively worse. I developed a simple on the car test to determine if the device had failed.

The weird part was that there were zero replacements in the USA both Bosch and Mercedes Benz. I finally got one from a Mercedes Dealer in Kansas that had one flown in from Germany. My 2.6 was down for two weeks, but I have other cars.

The accumulator holds about 20 cc of fuel under pressure, so if your fuel tank is very low and slosh uncovers the pickup, the system should maintain pressure for a few seconds before the fuel covers the pickup again.

Duke

Now that I have replaced the coolant pump due to a leaking seal, the engine refuses to start at all. My thought is to check fuel pressure at the fuel cooler inlet; what should the pressure be?

55 psi

Thanks; I’ll test it tomorrow.

The fuel cooler is in the return fuel line, downstream of the pressure regulator; it is at atmospheric pressure, hence, a gauge will show zero.