Misfires, possible coolant leak. Please help!

I have a 2001 Expedition Eddie Bauer 5.4L V8 with around 180k.
It has a rough idle, big loss in acceleration, it kind of “lurches” at times, gas mileage went all the way to about 5 mpg, etc. Also it has a constant, sometimes flashing CEL light. My scan tool showed two misfire codes- PO303 and 307. Also a pending code PO1405 which i found on here and it said it was a DPFE Sensor Upstream Hose Off Or Plugged.
A few weeks after the CEL light came on and it had the above symptoms, I noticed it was leaking coolant. I saw a very small amount leaking towards the top of the engine when it was running and I had to add coolant to the reservoir.
I thought it was most likely a coil pack or spark plug but does the coolant leak mean something different, or are those most likely two separate issues?

Have you looked at the condition of the plugs? When were they changed?

You have at least two issues.

The coolant could be leaking onto a plug causing a misfire. Fix the leak first and check out those plugs. Riding around with a misfire will eventually damage your catalytic converters.

Check the exhaust pipe for whitish smoke - a sign of water entering the combustion chamber. Also one early morning, with the engine cold, unscrew the coolant filler cap and have someone start the engine. If coolant bubbles upward upon starting, it is or both are signs of cylinder head gasket leaks.

Aspitler24 said:

I have a 2001 Expedition Eddie Bauer 5.4L V8 with around 180k.
It has a rough idle, big loss in acceleration, it kind of “lurches” at times, gas mileage went all the way to about 5 mpg, etc. Also it has a constant, sometimes flashing CEL light. My scan tool showed two misfire codes- PO303 and 307. Also a pending code PO1405 which i found on here and it said it was a DPFE Sensor Upstream Hose Off Or Plugged.
A few weeks after the CEL light came on and it had the above symptoms, I noticed it was leaking coolant. I saw a very small amount leaking towards the top of the engine when it was running and I had to add coolant to the reservoir.
I thought it was most likely a coil pack or spark plug but does the coolant leak mean something different, or are those most likely two separate issues?

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Trainmaster is probably right.

My 2001 4.6 had the same issue when I first bought it. Turns out that fluid was in the spark plug well. If the check engine light is flashing, don't drive it around too much. That's the computer telling you that the problem you're having is serious. And like he said, could melt the catalytic converter.

If you have to drive, take the road and go easy, but you want to try to avoid driving at all. Check spark plug 3 on the passenger side, get a flashlight and look down into the spark plug well. You may have to do a recording of it on your phone and flashlight if you can't see. As Trainmaster said you most likely have fluid down in there causing a no spark. Probably from the coolant leak. I would check cylinder 1 and 2 as well.. If you find fluid, the easiest thing to do is take the top of a spray bottle off, push the spray bottle hose down in the spark plug well and spray it out. The rest of it will burn off.. then clean or replace your spark plug.

The DPFE sensor could be unplugged or have a tear somewhere in it. Those things usually don't show codes unless it's for that reason.