[W126 Coupe] 1988 560 SEC blogs out?

[gerryvz]

Another way to check the ignition wires is to start and run the car in a dark garage.  Typically you'll see any arcing. What often happens is the ceramic insulators at the plug ends fails, which allows shorting (arcing) between the wire and the block. You can buy the insulators separately -- they're around $20 apiece and can be installed in about 5 minutes ... if that is the problem.

To really get a sense on what's happening with the ignition on your car, you need to take it to a shop where they can put it on a scope (oscilloscope). Takes about 30 seconds to hook it up, and the live graphs on screen will tell visually what is happening in each cylinder with the spark. If there's arcing/shorting you'll see it immediately in the electrical wave pattern for that cylinder.

Remove your distributor cap and check the contacts inside of it, as well as the rotor. Check all plug wire connections at the plugs and at the cap, as well as the center wire connections at the cap and the coil.

A vacuum leak will typically manifest itself in a fast or rough idle. This is often apparent by the ECONOMY needle. That needle should be on the left-side peg (or a millimeter or two off of the peg) at idle, and will shift to the right (red zone) when you accelerate and vacuum is developed in the intake manifold. If you are sitting at idle, and that needle is more than a millimeter or two to the right of that left-side peg, then you have a vacuum leak. It's not the only way to tell a vac leak, but it's a quick and clear one to diagnose many leaks.

Your problem does sound electrical though, not vacuum.

Cheers,
Gerry
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