I've been having issues with my 2002 E350 5.4 misfiring in the # 6 cylinder. Replaced the ignition coil first since it was throwing P0356, then it threw P0306 after the coil was installed. Got another coil to see if I got a bad one, and it's still misfiring. Went on and replaced the sparkplug, now it's throwing both P0306 & P0356. What could be causing this? I'm thinking injectors?

 

Both codes you list show something amiss in cylinder #6----injectors most likely not the problem at all.

P0356 is a problem with the ignition circuit which probably means there is an issue in the wiring leading to that cylinder's COP. I'd first check the chassis wiring harness connector to that COP, making sure the locking tab hasn't been broken. If it has the misfire if from it not properly latching to the COP.

If you're having a rough idle an easy test with engine running is carefully hold the connector to the COP, see if that changes anything. If it does, the connector is your issue.

If it doesn't then you'll need to begin checking that harness back to the ECM for an issue. A short of chafed bare wire could occur anywhere along that wiring path including in-line connector pins, perhaps all the way at the ECM plug as well.

Usually this is something local to the COP----pay close attention to that area first. Here's more help too:http://www.actron.com/code_lookup.php

HTH

 

Is the tab replaceable? Or would I need a complete new harness. Anyway to test the wire? I was thinking something had to be wrong with the wire, but the way they connect to the COP, replacing the tab connector would be easy, but the wire only has about 3" before it goes to the rest of the wiring harness.

 

The entire connector would need to be replaced, I use an NAPA part EC259, universal pigtail lead for all years of our modular motors.

The best test for the connector itself is with engine running and your manipulating where it joins the COP. If its not latching correctly and giving full contact you'll notice the rough idle disappear when you push them together.

If you replace the connector the replacement comes with at least 6" of lead which you would splice into the existing wiring harness. There is a way to replace just the connector but it requires purchasing some specialized service tools for automotive type connector housings. Trust me its easier to just splice in a new connector.

If that's the final fix make sure to use the heat shrinkable butt connectors for a good splice. Ford recommends soldering and heat shrink tubing for such replacements----your own skill and tool box will determine your choice here.

Hopefully this cures that pesky misfire. Please update us when you find the fix---it might be helpful to others down the road.

 

I'll give that a shot and see what happens. Thanks.