1997 f150, 4.6L, 88k miles

I know this issue has prolly been beaten to death, but i'm gettin desperate.

A month ago truck started shakin, and check engine light came on.
Took to Autozone, read cylinders 1 and 6 misfire, as well as a primary/secondary circuit fault(something wrong with coil pack).

Bought new plugs and wires. No Luck.
Bought POS cheap autozone coil packs. No luck.
Dealer installed one new Motorcraft coil pack, said other stock Motorcraft coil did not need replacing at that time.
Truck ran well for a month with occasional (once or twice per 20 miles) miss.
Full head shake returned with check engine light yesterday.
Code shows cylinders 1 and 6 misfiring again.
I hoped it was just the stock Motorcraft coil pack going out, but cylinders 1 and 6 are wired to the brand new Motorcraft coil pack they installed.

Do you think something could be knocking this coil pack out?
Does anyone have a clue what would cause a coil pack to keep goin out?
Could the wires be drawing too much current? The wires I bought were not Motorcraft(stupid ), and did not "snap" onto the coil pack as well as the stock Motorcraft ones, you think that could be a problem?

Is it just a coincidence that the misfire seemed to always return on an empty tank of gas, and returned in full fury with the check engine light after i filled up after running it down very low in fuel?

Could the fuel injectors need professional cleaning?

Out of ideas and dont want to be out of money by letting it sit at the dealership, any help would be appreciated.

 

Gig 'em Aggies!

You may have a combination of problems. I've seen the check engine light caused by a loose gas cap/faulty gas cap. If there is a seal, ensure it is intact.

If you continually run on an empty tank, you could be collecting condensation inside the tank, with water causing the misfire. I would put a good load of gas drier in the tank, fill it up, and keep it at 1/2 tank all the time. You'll probably want to change the fuel filter while you are at it.

What I've seen from water in the fuel, and loose gas caps, the computer doesn't really know what is wrong (it doesn't recognize a loose gas cap) and a code get thrown out.

Keep the troubleshooting simple. If you have changed plugs/wires, check all wires to ensure they are soundly pressed onto the plug. I have 1 plug wire right now that has backed off twice, resulting in a miss at idle and stumbling on acceleration.

I doubt if it's a coil pack.

 

Have your fuel injectors cleaned using one of those can kits.

You most likely have dirt in them from running your fuel tank low. Also change the fuel filter.

 

thanks for the replies. Funny you should mention the gas tank. About 3-4 months ago I let someone else fill up my gas tank and they lost the cap. Before i replaced it, a check engine light came on. I took it to autozone and the codes said improper fuel pressure and the guy said, "you got a gas cap on there?". Well i felt stupid, but i got a new one. I do tend to run it pretty low on gas, i didnt know that was so detrimental.

I've run a couple of fuel injector cleaners since the incident, but am thinkin about gettin a $99.00 fuel injector cleaning.

It wouldnt hurt to change the fuel filter, its prolly overdue anyway at 88000 miles.

 

I just had a simular problem with my 98. I had all ready changed the wires, plugs, and both coil packs a few weeks ago. then yesterday i was getting on it a little and around 3000 rpm it felt like it was missfiring alittle. so i changed the fuel filter and the miss gone.