98 Expedition - 5.4L 150K

I have a pesky misfire issue that is not going away. A little history - Changed all plugs, boots and 6 faulty COP's about a month ago. Prior to change, had no misfires. After plugs and COP's, engine missing sporadically under load at 50 MPH. No codes stored at that time. Now, missing is nearly continuous and codes P1309 and P0304 showing. I changed the #4 cylinder plug and put a new COP with boot. Still missing. Thinking that the new COP might have been faulty, I moved it to the #1 cylinder just for grins. Still missing.

I went out for a test drive and made several WOT runs and made the engine light blink but no codes are stored. I assume it will take a while to store the misfire again.

If anyone can guide me I'd appreciate it. I guess the last thing to do is change the CPS. If my #4 cylinder has a stuck valve or poor compression, will it show a misfire? I assume it won't since that is a mechanical issue and not an electrical issue. Thanks for the help!

 

Update - thought.....

I had no real misfire issues prior to changing all plugs and boots. I also changed the COP's that were out of range when I checked the resistance. Here's a thought. I've read elsewhere that these engines really like OEM ignition parts. Unfortunately, I replaced 7 of the COP's with Auto Zone parts. I hated to do it, but Ford wanted $100 vs. $39 for the Auto Zone parts. I hate crappy parts and senseless "lifetime" warranties. I want good parts but $800 for a set of COP's from Ford is outrageous!

Has anyone used aftermarket COP's with any luck? Just trying to lay this issue to rest!

 

Did you check & change the fuel injectors?

sounds like one of them is cracked.

I've used the EBAY cops & injectors with no problems.

 

Problem solved! Turned out to be a bad injector. I was very happy to feel a smooth running engine again after changing all of the parts. Still saved a great deal of money in repairs. Celebration to begin shortly!