Join Date: Apr 2010
Ferrari Life Posts: 2,199
Jack, you've done some good troubleshooting with limited resources.
Failed coils in COP systems can be tough to diagnose unless you have a specialised inductive pickup and a 'scope. However, if you have an old style inductive timing light, here's an alternative:
Buy a cheap set of 4 (or 8) spark plug leads, making sure that their distributor ends will fit in the ends of your coils snugly, without slipping out, and make good contact with the coil terminals. Also, ensure the spark plug end of the leads have long enough boots to go down into your plug wells and fit onto your plugs.
Now pull all the coils off the plugs on the bank where you suspect the bad coil, and fit these new spark plug leads between the coils and the plugs.
Start the car - it should run/idle no better or worse than before. If it doesn't, then you may have crossed a couple of leads, or possibly your wires aren't making good contact.
Clip your timing light onto each spark plug lead, and ensure you can see regular firing pulses. If any are irregular, there's your misfire. Note the cylinder(s) that are doing this and shut the engine off and repeat this test for the other side.
Then pull the spark plugs and compare them, as heavily fouled plugs present a very high resistance to the coil, and can keep a good coil from firing.
Note the cylinders that have fouled plugs and compare to the cylinders that weren't firing the timing light. The reason for the fouling should be investigated further as it could be an injector, or a failed valve guide or seal.
Put in a new set of plugs and repeat the test with the timing light, and see if any of the formerly misfiring cylinders are now firing OK. If they are, then you may not have an ignition problem, but an injector or a valve problem. Watch these cylinders in the future for a repeat of the same problem.
If you're still seeing misfiring with new plugs, then the coil(s) on those cylinders are likely to be dodgy.
I have a simulator where I test all my ignitions before sending them out, and I'd be happy to test any suspect coils for you and take a video of them firing (or not). Drop me a PM if interested.
'99 550, Rosso Corsa / Nero, S/N:114654, Assy: 31836, Engine: 52084
High mileage, low compression, and missing on a few cylinders.....just like my cars.
Maranello Skunkworks Team Member