How to test a coil or plug when it is beneath the intake plenum without removing

Does anyone know how to test coils or plugs without removing them when they are in difficult spots under plenum, can you do it through the fuse box please help

Depending on what info you are trying to find, if you can access the wire harness that connects to the coil, you can see if there is batt voltage, signal, and ground to the coil.

Depending on what info you are trying to find, if you can access the wire harness that connects to the coil, you can see if there is batt voltage, signal, and ground to the coil. You'd need to back probe one wire at a time. Depending on the design, with key turned to ACC assuming only two wires both should/could have 12v until unplugged from coil then one should go to ground. multimeter is good with one lead to ground but don't stick it into unplugged harness or it might not make good contact when plugged back in. Just touch inside harness or just back probe with needle. When plugged into harness and car running that signal wire should have a pulse to it letting you know it's receiving signal from igniter and/or PCM.

There's definitely options, depending on the application and coil design. Something like an AESWave Paddle Probe works perfectly on Ford two wire coils, especially ones under the intake on 3.0L engines.

www.aeswave.com/COP-Secondary-Paddle-Lead-Capacitive-p9151.html

Getting coil current ramps from the fuse box is also possible if you know which fuse powers the coils. This method can be made more difficult when that same fuse also powers other components. :silly: An amp probe and current loop are required.

www.aeswave.com/Current-Probe-Low-range-...ana-Plugs-p9501.html

www.aeswave.com/Fuse-Amp-Loop-with-Voltage-Tap-p9653.html

If nothing else, some vehicles make it easy to get primary voltage waveforms due to harness design. Pentastar 3.6L engines typically run all their coil control wires through C130 at the rear of the left bank cylinder head. That makes for easy scoping of all six coils in one location.

I didn't think of the fuse box. I've seen the paddle probe and that's a great option that helps to keeps the frustration level down. I'll have to remember the fuse box, thanks for the education.