How many times have you tried to find the misfiring cylinder on a Ford COP (Coil On Plug) ignition system without losing your mind?
Here is at least one way to find a secondary misfire with just a scope. Lets say you get a Ford COP system with the complaint of a check engine light and/or misfire. You get the vehicle and if the check engine light is on you retrieve a P0300. Where do you go now? What I do is feel the misfire out and try to determine by feel if it is the ignition system or not. An ignition misfire is usually sharper feeling then other types of misfires. I also scan the vehicle for codes and look through the data stream to see if anything looks out of place. If everything looks good, I then consider plugs and coil boots based on mileage and repair history. You don’t need to do an ignition tune-up for this to work but it is usually
needed and sometimes is the cause of the misfire. Ok, now the scan data looks good, no codes besides maybe a P0300 series code, and even the plugs and coil boots may be new. There is still a sharp ignition type misfire, what do I do? You can use mode 6 data and see what cylinder has the most misfires. This would be my back up, but I have seen this data telling a different story than I end up finding. One thing to keep in mind is mode 6 misfire data isn’t live, so beware. What I
do, is hook up one lead to the easiest to probe injector I can find. This will be my trigger which I will use with the vehicles firing order. Next, I probe the power supply/supplies for the ignition coils. You can now see the coils turning on and off from 0v to 14v. Some Fords have the multi-strike ignition system where you will see the coil fire up to 3 times in one firing event. With everything hooked up, I will then disconnect one coil to find its relationship to my injector trigger. Now I will do what has to be done to get the vehicle to misfire which may include; snap throttle, power breaking, leaning the engine out, or just waiting it out. If you have a secondary ignition problem, you will see it on the coil primary scope trace by the voltage spikes. If the coil primary circuit opens up you will also see this by the loss of a coil pattern, just like you did when you unplugged a coil . All that is left is to use the firing order, injector trigger, and primary coil trace to find the exact cylinder or cylinders with your ignition problem. I hope this saves all of you a headache in the future.
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