Spark plug problems

[venus5764]

Help!

I have an on going problem with my 2000 Ford Ranger 4.0 ltr, V6.
Usually the number 4 cylinder needs replacing due to a cracked porcelain base. The last time it had a lot of oil around it. Now the codes PO174, P1151, PO306, and Cat fault are coming up. The engine light remains on.

This is the history of the repairs performed to date.

New fuel injector
New plenum gasket set
Replaced cyl 4 spark plug due to broken porcelain eight times over the course of two years.
One of the times that the #4 needed replaced the long term fuel trim running +13 on bank 2 and +9 on bank 1, replaced spark plug and all numbers returned to normal.
All spark plugs and wires replaced twice over the course of two years.
Replaced the intake gaskets
Replaced fuel filter twice.
Valve covers leaking…
Injector flush.
Flushed transmission
Cooling system flush twice
New thermostat
Currently #6 and #4 cyl are giving me problems and the pick up continues to have the same issues. A smell similar to that of a hot radiator emits just before the trouble starts again. I have had the radiator checked and no leaks were found.

Repairs were performed at three separate repair shops, and Ford being one of them.

Any suggestions would be appreciated.

 

[steve01]

I wonder if at a certain temp you have a head gasket leaking. That would explain the smell before the problem starts. Maybe get your engine warm and do a leak down test on #4 and #6. Or maybe just put 150 or so psi of air into #4 and #6 and see if you get air bubbles in your radiator. I'm no expert at this it's just what sound rite to me.