Engine misses at 35 mph code po 304 coil pack plug wire replaced

Here's a link to some help on your P0304 code. P0304 OBD II Trouble Code

Change the spark plugs end wires. One bad plug or a wire can cause a miss like you wouldn,t belive. Evan on a vehicle with low miles on it.

I would start with switching a coil, swap # 4 coil to another spot and see if the misfire moves, the coils on this van operate to cylinders so move it and see if the misfire changes then you know its the coil and if it does not then next thing is to check spark plug and wire, replace the plug and wire and if that solves it then tune up van, good day,

having PO 304 = Misfire cylinder 4,PO 306 = Misfire cylinder 6, as I read above you have done the most. The thing that you have missed is to check whether the Catalytic Converter is faulty or not. To get an idea check whether you have a smell like rotten eggs at the end of the exhaust,you start having problems with cat and needs replacement. My advice before you go for a cat replacement is good to visit an MOT center and check your emissions and then you decide,

Its either fouled or worn sparkplugs,sparkplug wires or dirty,clogged injectors or injector wire harness.

IGNITION COILS, PLUGS, WIRES
1 COIL FOR 2 WIRES. PULL TWO WIRES ON COIL HAVE SOME START CAR IF ARCH TOUCHES EACH TOWER COIL IS GOOD. IF ARCH GOES TO TOWER AND BACK DOWN TO BOTTOWN OF COIL THAT INDICATES BAD COIL. IF COILS ARE OKAY THEN CHECK WIRES AND PLUGS.

Hello Bret.
These codes are indicating engine misfires. 303 is cylinder #3 and 304 is cylinder #4. The 316 indicates that the misfire happened in the first 1000 revolutions.
These trucks are notorious for misfires. The most common issue is ignition coil failure. Failure on these coils can be accelerated though by spark plugs that are worn and contamination from oils, antifreeze leaks and water.
If it has been some time since you have replaced the spark plugs this may be an opportune time to do so. This job isn't for the faint of heart or those with little patience. Some of the coils and plugs are difficult to access, especially #7 and # 8. I also recommend torquing the spark plugs properly as there are some thread stripping issues on the spark plug threads with these engines.
Have at least 2 new coil assembly's for the two cylinders that are misfiring and be prepared to find at least one more that looks poor. I have used some aftermarket coils but have had issues with them. Ford has reduced the price on their coils to reflect a more fair market value so I would use those.
Have a look for any contamination issues and repair those to prevent future problems.
Hope this helps you along.

ck if you have spark at the coil for that cylinder. check the plug wire closely. if it has spark at the coil, then replace all the spark plug wires.

Could be the coil pack should be read in ohms about 7 to be good

You need to drain some coolant. Loosen and disconnect water lines by the firewall- the ones in the way of your wire change. u need to get a diagram of the firing order of the engine so that those wires are correctly connected to the coil packs.