Vehicle: 2013 Ford® Fusion. Having a hard time figuring out whether or not an ignition coil is bad? In this Diagnostic Quick Tip, National Field Trainer Jason Gabrenas shows you how to use a low amps probe to perform a current ramp test.
There's many different ways to diagnose ignition problems, maybe a faulty ignition coil or something to that nature, using a scope. Today we're going to talk about doing a Coil Current Ramp Test.
I already have the low amps probe hooked up around one of the wires on the number one coil. I have my settings in the lab scope, I am on 10 amp scale and a 10 millisecond sweep.
We've got it recording so let's go start the vehicle up and see what it looks like. I'll pause this after a few seconds and shut off the car.
Here we see a good coil pattern. Ford, at idle, uses what's called a multi-strike ignition. It's trying to dissipate all the extra electricity in that coil by firing multiple times.
That also helps the fuel burn a lot better at idle. I've even seen some BMWs do four or five multiple strikes just to dissipate all that energy.
We turn on our cursors and take a better look at this timing of this pattern. If I go in and measure the first strike there, because that's the one we're really concerned about, you get about 1.32 milliseconds.
A good average would be about one and a half milliseconds so we're well within that. You also want to make sure that the current ramp is nice and smooth. It makes a nice little smooth line there.
If it looked anything like the second or third strikes there and it ramped up real quick and then over, you would have an issue with a high current flowing through that coil driver.
You also want to make sure that there isn't a weird curve or anything like that. It needs to be nice and straight. So if it was curvy, that would show another issue with the coil.
It's a pretty unobtrusive test that you can do on these coils. You just have to put the low amps probe around one wire in the circuit, and you can test it and take a good look at it, which will make your life a little easier.