Art20c

Hi guys,
My engine on 87 928S4 is missing some times on idle, somteimes on high RPM. Checked distributor caps, etc. What I found is that if I disconnect driver side ignition coil wire from the coil while engine running there are visible sparks flying between coil terminals and from high voltage terminal to those terminals. It looks like electical X-tree. Is that a sign of a bad coil?
Please help!

Nicole

It's amazing that you are still alive - I would not touch this ignition system unless everything is turned off... It can kill you!

Barry Johnson

Someone else chime in here, but I think that if you hold the wire in front of the coil while its running, it will still ark between the two, and sometimes send you flying about 10 feet backwards, not that I've tried it (I have my little brother test the spark <img border="0" title="" alt="[Wink]" src="wink.gif" /> ). If you're missing at high revs, that (from what I've heard, never done it, yet) it sounds like a coil going out, but it could also be bad plug wires. Is the insulation around the wires cracking and brittle? If you have the engine running in a very dark area, such as at night, you can sometimes see little arks around your wires - sign of bad wires. By the way, how are your plugs? I replaced mine with the Beru Ultra +4s, and what a difference they made! Got them at Devek. If someone else is reading this, does it sound to you that it is a bad coil? I sometimes have the same hesitation at high revs.

Jim bailey - 928 International

Porsche in the workshop manuals states " Never disconnect the ignition lead....while the engine is running "...further states "there must be no flash over from coil terminal 4 to coil terminal 1 and 15 , or the control unit could be damaged beyond repair" . So this inferes that if you do pull off the coil lead it can jump to terminals 1 and 15 . You are playing Russian Roulette with a loaded gun and may do serious damage either to yourself or the electronics of your car .

Art20c

Ign wires ok, I didn't pull wire out off running car. It was running on 4 cyl just for a moment. I know it could damage cat and control unit, but still is that a sign of a bad coil?
P.S. If I connect coil wire to coil loose, leaving the gap, the engine runs like a clock.

Nicole

To the best of my knowledge, bad coils rarely cause idle problems. When chasing an erratic idle problem on my car we replaced the coils, because they was the last "old" parts of the ignition. It made just as much difference as replacing the wires, plugs, rotors and caps: NONE.

Then a compression test revealed fluctuations between the cylinders. I ran heavy doses of valve cleaner, and had a Rislone treatment and oil change done afterwards. Since then the car runs almost as if it was brand new.