GB17

I recently bought an 05 F150 FX4 with the 5.4 and it has miss on 2. It was missing for at least 2 months before I bought it. I figured it was just a spark plug issue and that it would be easy to fix... I was wrong.

I have replaced the coil pack, plug, injector, and gotten a compression test. The compression was about the same as the other cylinders according to the mechanic. He then checked the wires coming to the plug from the ECM and he said there was no signal at the plug or at the injector. He checked the wires for continuity and said there were no broken wires and concluded that it was the ECM. About $300 later, that new ECM didn't fix the issue. I need to know what is causing this. Everyone else I've asked is stumped.

I'm giving it one last shot before I just take it to the dealership and let them find the issue and deal with it. & It's going to be $100 just to have them look at it.

Martian

If there's no signal but the wires are continuous. sounds like you have a short in those wires somewhere. Keep tracing them. Also make sure your connectors are attached to the wires properly on everything.

GB17

So its possible for a wire to not be broken, but to have a short at the same time?

Martian

Yes. You could have two wires shorted together and yet they're still continuous, so you'll have both a short AND a continuous wire. Did the techs also test for input coming from their ultimate source?

GB17

He took a volt meter and put a pin in above the connector for the coil pack, traced the wires, and put the other pin in the bundle right before the connector at the ECM. It was cheap, but he said he was giving me a discount because I'm in high school and knows I couldn't afford the full price.

Martian

Hell, you could've done that with a $15 meter from Harbor Freight... but did he actually test the bundle for voltage, not resistance? I.E. engine running, wires tapped into the coil connector's (and injector connector's, for that matter) leads to see if there was actually any signal there?

Martian

This is actually written very well.

http://easyautodiagnostics.com/misc-...p-coil-tests-2

GB17

Yeah but the compression test was included and I didn't know how to do that. He also hooked up a scanner and read all the engine conditions as it was running. I know that he had me turn the car to accessory for a long time, but I don't remember if I started the engine for him or not.
I'm going to get a volt meter and check everything again. How would I check for a short, voltage, and resistance? (the most I've done is listen for a beep when wired a light bar on my last truck)

Martian

That was to pull codes. You can also do that yourself. Go online to eBay or Amazon and get yourself a ~$20ish Bluetooth OBDII scanner, then $5 gets you the Torque Pro app on your phone. A lot of us around here have that. As for compression, I doubt you'll ever need to do a compression test again, but you can get a compression tester also from HF.

You need a multimeter. If you have the cash, get a GOOD one (i.e. at least $50... I think mine was $70 at Lowes). TAKE CARE OF THAT THING. It will prove to be one of the most useful things you will ever own in your life.

To test for a short, basically you'd set the meter to Resistance, put one test lead on one of the leads for the coil, then move the other test lead across the other wires to see if you eventually get a reading. If you get a reading on any other wire other than the same one the other test lead is on, you're shorted to that particular wire.

GB17

Okay, I will try to test the wires again tonight and get back to you.