$480 @ dealers and still no clue
 

Greetings all!

I have a 1999 F150 XLT off-road model with a 5.4L and 144k miles. I have spent a total of $480 at two different dealers with no answer to my trucks problem. My truck runs great when it's cool outside, when it gets above about 80-85 it starts to run really bad- like its vapor locking, but it's injected. To get anywhere when it's hot, I often have to stop and let the engine cool down. Things I have done or had checked, or the shop has:

1. Replaced fuel cap
2. Replaced fuel pump
3. Replaced all coils
4. Replaced fuel filter
5. Replaced all plugs

Evap system pressure checked/smoke checked
Fuel pressure is good
There are no codes thrown, no codes stored
Heat sensor checks good

Both dealers have not been able to replicate or fix the problem (it's never been that warm outside when they've had it).

A couple years ago my truck was running bad, as I have described and a mechanic found the aft evap return line valve on top of the fuel tank cracked, and almost ready to fall off. He replaced it and I was good to good for a couple years. I might note the symptoms were the same, like it was vapor locking- this is why I had the evap system pressure and smoke checked.

I don't know what to replace next? Perhaps the ECU/PCU? But don't they throw codes like crazy when they go bad?

It's a great truck, but it's no longer reliable, and I can't sell it knowing this will cause problems for a new owner, and can't take the hit for selling a broke truck.

Shall I pull the VIN, light it on fire, and push it over a cliff?

I know there is a solution to every problem, but I just don't have the money to buy a new truck!

I'd be forever grateful if someone could lead me to the problem, and a fix. Any Friks or Fraks out there? Perhaps Ford whisperers? Heck, I'd even send you Christmas cards every year, if you lead me to a fix.

Best Regards,

Hopefull!