I recently bought a new bosch coil on my 1989 volvo. Every so often my ignition wires would misfire and I would play with the wires..pulling then off the sparkplugs and then it would be fine. I even put new bosch wires in. So the question I am asking can a coil get a little weaker after 10 years of use..even by lets say 10%. Is it always an all or nothing situation. When I had a volvo turbo diesel, I would have a really hard time starting it. Turned out that the starter motors can work but lose theit starting torque so they dont turn it fast enough. That one was realy tricky to fiqure out. Any ideas about the coil I put in or did I waste my money...Leo

Coils can fail in a way that you get a weaker spark, however such fails are rare. E-mail me if you want gory details. The input voltage pulse switching is more important. One other thing to look for is plug wires cross firing or firing to a metal ground, sometimes can be seen in the dark. Some car makers not only use looms, but also specific order to run wires. Good plug leads are also important as many are really a nylon core with carbon impregnated in the name of static suppression. I have seen a couple cases where that conductor was broken inside causing misfires and one case on a new set of yellow wires.

Leo,

I would imagine that if the coil failed, it would fail completely and not gradually, but I'm by no means an expert.

Did the misfiring stop after you replaced the plug wires? I'm assuming that you wouldn't have replaced the coil if it did, but your post is a little vague. How about the plugs themselves? Cap? Rotor?

(AFAIK, coil failure is relatively rare on RWD Volvos.)


-Jim