Good evening,

Sorry this is a little long.

I have a 2006 Expedition, 5.4L, 175,000 miles. Bought it used 2 years ago. About 2 months after buying it, it suddenly gave me problems going up hill. The CEL lit up and I had a P0304 error. I replaced all of the COP and it seemed to fix the issue. Over the next year and a half, the same issue has popped up a few times. I have reseated connections to COP #4 and swapped the COP with another and it would fix the issue for a bit.

Late last summer I got another P0304 code and I couldn't get it to go away with reseating connections and swapping the COPs. I finally replaced the spark plug in #4 (Champion) and this fixed the issue for a few months. About 4 weeks ago the issue came back. Tried swapping COPs again but no fix. Installed a Motorcraft plug in case the Champion wasn't quite right. This fixed the issue, but the next day I started getting a P0303 error. I tried swapping the COP #3 with another but no fix. Replaced the spark plug last week and no fix. I initially received codes P0303, P0357 & P0353 and it ran very rough. I reseated connections again and when I reinstalled everything, I was down to just the original P0303 code.

Today I replaced the rest of the spark plugs and now it runs much worse. It isn't giving a code but I don't know that I could drive it around the block. In neutral, it idles a little rough but the truck rocks when I give it gas. In gear it feels like it wants to die.

When I've done any work on #3 or #4, I've pulled the PCM for easier access. Tomorrow I'll check the connections in the PCM and the wiring to the COP and fuel injector.

Am I heading the right direction?

Thanks,
Steve

 

You might have to give it a couple of days to relearn how to control the engine. All of that information is lost every time the ECM is powered down.

BTW, have you ever tested the fuel pressure?

 

I haven't checked the fuel pressure. I replaced a few of the spark plugs again and restarted the truck after each one. On the 3rd one, cyclinder 1, it started up normal and ran much better. Not sure if it is a bad plug or something was reseated. I did notice that the insulator below the electrode was almost black. Same as the first one I swapped the 2nd time. The 2nd plug I swapped was still white. Since I first replaced them 2 days ago, they only ran about a mile and for maybe 10 minutes total. Oh well, I'll keep an eye on them.

Steve

 

Keep an eye on the heater hose that runs over the 3 & 4 cylinders. On certain models others have reported this hose leaking coolant down into the 3 & 4 cylinders, resulting in misfires.

 

Thanks again. I'll keep an eye out on the hose. I haven't noticed any fluids in the spark plug wells.

After getting it running better with a second spark plug swap, it seems to have lower than normal RPMs. I drove a few miles to the gas station to fill it up and test drive it (55 mph). It stalled out as I stopped at a pump. I gassed up and added some injector cleaner to the tank. I was able to start right up but the RPMs were still low, about 500 - 600. Normally it sits at about 750 - 800. It drove home ok and is still just a little under powered but the accelerator response is pretty good. Not sure where to go from here.

 

At first I was thinking your idle RPM issues might be related to the IAC valve.
But, I think your year engine uses an electronic throttle body with a stepper motor.
Have you tried cleaning the throttle body?

 

I'll check the throttle body tomorrow. It used to be fine but for the past few weeks, I've had odd misfires and I think I have them fixed now. Thanks for the help.

 

Cleaned the throttle body and mass airflow sensor a few days ago. Still runs rough.

The error codes after that were P0171 (too lean), P0300 (multiple misfires), P0302 (Cyl 2 misfire), P0303 (Cyl 3 misfire) and P0356 (Pri/Sec circuit malfuntion Cyl 6).

I reset the codes and drove to the store and back. Now the codes are P0302 and P0303.

I've reseated electrical connections many times over the past few months. I've swapped and replace CoP and replaced spark plugs. Is there a chance that the ECM is bad?

Steve

 

What about the fuel injectors for cylinders 2 & 3? Have you swapped them with other cylinders to see if the codes move around?

 

Not yet. I've only just figured out how to get to them. The last time I spent more than a few minutes under a hood, there was a carb and no computer. It looks like I have to remove both sides since both rails are connected and I will need a warmer day. Hopefully tomorrow.

 

It's possible, but near the bottom of the list of things that can go wrong.
The PCM appears to be determining when to fire all the other plugs properly and it seems your problems are now with just #2 & #3.
The PCM completes the circuits by grounding the 12v after going thru the coils and injectors.
You may have wiring that is marginal, a crack in the coil housing, a fuel injector screen clogged, sticky fuel injector, marginal plug boots, connector lock tabs broken.
Have you checked the fuel pressure at the test port and what is it?
Has the fuel filter ever been replaced?

 

I've swapped the coils numerous times between different cylinders but not usually the same ones. The problem has never followed a coil. I've checked the connectors a few times since I know the tabs can break but they are snug and click when I reseat them. I haven't checked the fuel pressure but will add it to the list of things to look up for testing. I've cleaned the mass airflow sensor and throttle body in case there were issues there but no help. I haven't replaced the fuel filter recently and not sure if I had it done closer to 2 years ago. Probably not since I hadn't had any issue then.

 

The fuel filter is probably fine.
Harbor Freight has an adequate fuel injection pump tester #62623 for under $20 with coupon that is handy to have.

 

I'll look them up. It runs better at higher RPMs. It hiccups at 1900 - 2000 RPM and idles around 500. I haven't received a new CEL since the resetting connections yesterday but it is still rough riding.

 

There's no test port on the fuel rail on the returnless system for the 3v engines. But you can read the fuel pressure from Torque through OBD.