I'm a newby so forgive me if this is in the wrong spot. I bought a 1997 F-150 4x4 4.6 auto last night and now its throwing these codes, PO305 and PO306. I've researched them and found out its a misfire on 5 and 6 cylinders. The truck has 97,000 miles on it. Has anyone had these codes before and what should I check first? Plugs, wires, coil packs? I should go back and give the guy a few words because I know he had to of reset the computer before I drove it. Thanks in advance.

 

Do a search for misfires.

 

Thanks.

 

First thing I would do is check the coil pack and boot and plug for carbon tracks. Being a 97 the boots are probably dry and letting spark leak. If all looks good in the ignition department... the injector is still a possibility.

 

Plugs and wires, definitely. Use good ones, no auto part store cheapies.

Stick with Motorcraft or Autolite plugs and wires (unless you know what you're doing).

Coils are unlikely, but possible.

Steve

 

Thanks for the replys, I'll check the plugs and wires today.

 

I put MSD 8.8 wires and Denso Iridium plugs in my 97 @ 100kmi and i now have 132k on it with no problems.

 

Those are VERY good plugs and wires. I'd be interested in learning how long they last, overall. 32K is pretty short so far.

Steve

 

Misfire fixed. I bought the truck 2 weeks ago and apparently before I went to look at it the guy pressure washed the engine. Well it did well on the test drive but soon after I paid for it and was on my way home the misfire started. Finally got time today to change the plugs and wires. Bingo, there was standing water in the 2 sparkplug holes that I was getting my misfire in. The design of the 4.6 lets water get trapped in the sparkplug holes very easy. I bought Motorcraft plugs and they were out of Motorcraft wires so I went with Borg Warner. They said they were better, who knows. I would like to know why the wires are never the same length as the ones I remove. I bought them for my year but I'm left with 1 wire way too long for where it needs to go.