have a 97 F150 4.6 l. I changed the plugs and wires at 98,000 and 198,000 for second time. I had the coils changed at 198,000. Truck ran good for a few miles and took back to shop. New wire to #6 had gone bad but was in warranty
so had it replaced. Everything was ok for a couple of months then CEL light began blinking. Mechanic told me that my cat had a crack in it but that I could keep driving it.

Truck runs bad and mis-fires going uphill and wastes gas. I see from other posts that the ECM is trying to save the motor from catching on fire.

Took truck to local Ford dealer, (now at 212,000 miles) and they said they needed to install new plugs and wires first to try to determine what else may be wrong. While there, they changed a strap on my gas tank that was under recall, now the gas tank is leaking gas. They did not mention anything about their having read any diagnostic codes or having put it on a scope.

This truck has always been dependable so I'd like to get it fixed but not for hundreds or thousands of dollars without know what is actually wrong.

Any suggestions?

Thank you

 

Start with the gas tank first. At the age of the truck the tank is already rotted through under where the old straps rested. You have to bite the bullet on a replacement tank. Strap replacement resulting in a leaking old tank is not the dealer responsibility. You must fix this to be safe.
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On the misfire, you 'may have' already ruined one or both cats from the misfire. The motor passes raw gas into the cats where is lights off sending the cat temperature over 1000 degrees. They will not stand that high a temperature without melting and blocking the inlet/outlet making the motor difficult making any power. You will need Ox sensors as well.
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As far the misfire, there is no excuse for not finding the cylinder/s at fault by anyone with a Scanner that knows how to use it.
Look at live data and mode 6, test 53 at all cylinder misfire monitors for the offending cylinder with high counts.
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As far as when and how often anything was replaced it make no difference when you have a problem. Replace what needs to be, to resolve the issues.
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You may need a coil, wires and or cats and a fuel tank..
Dealer bill for these items and labor will ruin a thousand dollar bill in a hurry.
Do what it takes and get to a good shop that understands this.
Good luck.