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I have a 1988 560sl that is an occassional driver. It has 120,000 miles on and has never given much trouble. It had not been driven in 6-8 weeks and when I tried to start it, the engine would spin but not start. It has a new fuel filter and fresh gas in the tank. I was concerned that the fuel pump relay had failed but when I check the pump with a test light, it operated properly. The part that I can't figure out is that when I first try to start it, the engine will fire as if to crank but then just spins. If I walk away for thirty minutes or so and try it again, it does the exact same thing, the engine fires and quits. I put fuel down the intake and it will fire and run for a few seconds and then cut off. Can the fuel system have air in the line? I'm not very familiar with fuel injection systems. I had a car in the past that had been parked for a long time and the fuel solidified and clogged the lines. Any chance this is my problem? Any ideas?
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1988, 1989 MB 560SL/ 1995 MB E320 SW
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Engines are easy if you get back to basics.

An Engine needs three things to operate (assuming no mechanical issues or failures), fuel, air and ignition.

Start by eliminating the culprit by testing the three items necessary for operation.

If it starts it probably has ignition. You can test this by removing the distributor lead and looking for the spark while someone cranks the engine. Be careful to not hold the exposed end or you will get a shock. Hold the lead near the connection on the distributor cap where you removed the wire and you should see a strong spark that will jump the gap. If not, move the lead closer to the connection until you see a spark jump the gap. No or weak spark, suspect an ignition coil.

You could have a mechanical problem inside the distributor. I do not know if your model has a rotor but I think it does. If the rotor arm is broken or damaged, this could cause the spark not to get to the correct spark plug or ground off to somewhere else. An engine can run but it will not run very well with this malfunction. Take the distributor cap off and take a look inside. The cap should not be cracked. Examine the inside of the cap. Look for carbon trails that might indicate an very small crack that is barely visible to the unaided eye.

Examine the rotor for cracks or damage. The contacts should be bright with a little contact corrosion due to normal wear. Very worn or blackenend contact areas indicate arcing and poor conductivity which will degrade the ability of the distributor to do its job correctly.

Once you have eliminated the coil and distributor, you still have the spark plug wires and spark plugs themselves to check. However, your description does not lead me to suspect a massive simultaneous wire and plug failure. However, be sure to check the coil to distributor lead as that is a single failure component to the system that if degraded could cause a general running problem.

Next investigate the air intake system. If your care was sitting for awhile, something could have crawled into your ram air tube and is blocking your air to the engine. Take off the air cleaner cover and take a look. It should be relatively clean in there with some normal amount of dirt and dust depending on how long ago the filter was replaced. Anything that might indicate you have an air supply blockage should be addressed and corrected. Again from your description, I would not suspect this but check and eliminate anyway.

Even though you think you have good gas and have recently replaced the fuel filter, your problem seems to indicate a fuel starvation issue. A blackage could have occurred in the fuel filter. That is its job to protect the engine by stopping bad stuff from getting by it. Maybe it just did its job. A faulty fuel pump could also be causing the same symptoms that you describe. You may be able to remove a fuel supply line and capture the fuel as it flows from the line into a container.

CAUTION: Fuel is very flammable. Do not do this near a hot engine or source of flame or ignition. You will get a nasty surprise. (How do I know this?)

If you are not familiar with the procedures that I have just described or feel uncomfortable attempting to troubleshoot your vehicle, get a knowledgeable friend to assist you or take it to your friendly neighborhood MB mechanic.

I have tried to give you a clue without getting into specifics. I hope that I haven't steered you wrong or bored you with the basics.

Jim
 
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