I have a cylinder 4 misfire detected throwing code P0304.. Truck runs rough then if I put gas in it it does fine.. Any ideas? Plugs and wires? Coil pack?

 

Is this on the new truck? When's the last time plugs were done? How many miles are on it?

I would make sure the coils are all connected and everything is bolted down good. You can always try swapping plug/ coil to another cylinder to see if the misfire moves. If it does you've found your problem. Might be in your best interest to replace all plugs and coils if they haven't been done in a while...

 

Sounds just like a coil/cop, not sure on your model year.

$30 dollar fix, no worries

 

Yeah it's on the new truck.. Guy I bought it from said he replaced 2 coils on it.. I have no idea why he didn't replace them all at once..

 

Just went to the gas station and my oil pressure gauge dropped and the light came on.. When I got back in the truck and turned it on it was back to normal?

 

Since our trucks don't really use an oil pressure sender that reads actual pressure (it reads if there is at least 7 lbs of pressure and turns off the light and sets the gauge), it most likely is a bad connection (at the sender). The switch itself might be oily or faulty and causing a low reading, setting off the o/p light.

Check your fuel tank vent valve for obstructions and dirt. When they get clogged or dirty they can (for some damn reason) cause an engine misfire.

 

I wonder if this is why mine is idling rough

 

I agree with this guy. I just got a 2000 5.4 the guy told me his mechanic told him it needed a coil pack and tune up, after testing the coils/injectors I swapped the coil, no change in my Misfire, swapped the injector, no change, put new plugs in, still no change, so I tested compression... ... 0 psi in cylinder 1 65 psi in 5 and 150 in 6. I am po'd about needing to replace the motor now, since I just got laid off, too.

Anyway, try swapping the coils/injectors and see what that gets you.

 

How much did is a new motor gonna run you?

 

If it is just the number 4 cylinder, check the spark plug socket for coolant. Those heater hoses over the number 4 cylinder can leak causing a misfire. I would suggest taking out the plug, cleaning out the plug socket with a round wire brush, WD40 and rags, clean the COP connection, and put it back together. Use di-electric grease on the plug/cop connections.

While cleaning look for signs of engine coolant or oil. If you find any, you most likely have a coolant leak of a oil leak at your valve covers. After doing all of that, it will most likely run fine for a little while and then start missing again as that water starts to leak and get down into the plug socket. The leaks usually start around the quick disconnect fittings of the heater hoses next to the firewall. since they are usually small leaks, you will hardly notice them because they evaporate when the coolant hits the hot engine. they can however cause a really bad miss.