Hi,

I have a misfire on my #5 cylinder in my 1998 F-150 4.6L V8. It sorta was coming and going.. at times it seems like it just wasn't firing, then every once in a while it'd just miss.

Well, I've replaced the spark plug wire, and it seems to have helped slightly, although I'm not sure - since it's semi-inconsistent. Definitely didn't 100% fix it.

I recently (10k miles ago) replaced all my plugs with Double Platinum Motorcraft or whatever brand it is now.

I tried changing out the spark plug (same model) and it still missed.

I'm wondering, is this is a problem with my coil pack? This 4.6L has two coil packs.. each one has 4 caps on it.

I bought a new one for $57, and am wondering if I should try putting it on? Once I put it on, I don't think I'll be able to return it.

Is there anyway for me to deductively identify what the problem is? Injector?

Additionally.. the miss either doesn't happen or is less noticeable at higher RPMs - if this helps any.

Thanks for any assistance.
anx

 

Ok more info...

I disconnected the electrical thing that is plugged into the injector and it just emphasized the subtle miss that was already there. In other words, what would sometimes be a miss - with the injector electrical thing off was constant.

I pulled the plug and it looked like a plug running too lean? Really white at the tip. I've attached a pic:



I put in a new plug and it still has the ever so slight miss at low idles.

Fuel injector bad?

 

I had the same problem, and I replaced wires and plugs and coil packs and all kinds of stuff all kinds of times, and it turns out that it was a bad fuel filter. Normally, my plugs were globbed up with crap when I took them out, so I can't verify the white tip, but a fuel filter is cheap and it can't hurt to change it, and it may take care of your problem.

 

Could a bad fuel filter cause just one cylinder to misfire?

Where is the fuel filter located? How hard is it to get to, and what is the estimated time for an intermediate like me?

Thanks

 

Your fuel filter is located along the inside of the drivers side frame of the truck and requires much monkeying to replace. I would buy a good metal fuel filter remover tool (8.00) versus the plastic kind and be careful of getting fuel in your face when it does release. The fuel line has a fitting that requires you to insert the tool in the female connector and pull straight back towards the fuel line while at the same time pulling the filter away from the fuel line. You must do this at both connector ends. One end is easier to remove I can't remember which one though. Good Luck!

 

anx,

I'd suspect a vacuum leak or "un-metered air" entering some way. Since the mis is #5 I'd start looking for leaks in and around the drivers side head.

Do a search on "vacuum leak" to see where to start.

Good Luck,
Bill