I have a '97 F-150, 4.2L 5 speed, 4x2

The engine has been experience a few "wierd" problems that I think might be related.

1) The oil pressure guage will drop when the truck is revved (more so under load).... ie put the truck in 2nd gear doing 40km/h and above, mash the gas and you can get the oil pressure guage from just under 2/3 of the way up to just above the low mark.

2) The truck occationally (more often lately) will make a horriable tapping noise when it first starts up. This will last from 2-3 seconds up to about 15 mins after the inital start-up. The tapping noise is directly proportional to the RPM's of the engine an at idle happens about 5-6 times a second. After the sound goes away, it will not comeback untill you restart the truck.

History of the truck..... I bough the truck used with 40,000+ km on the odo, 2 years old. Since then it has seen regular oil changes (every 5000km with castrol 5w-30). I use a Motomaster oil filter (from the dealer). The truck now has approx 240,000km on the ODO. I did try changing the oil and it didn't seem to help (both the tapping noise or the "dropping" oil pressure). I have checked and the oil is up to the full mark.

I have performed a search on the fourm and a few things have caugh my attention.

A) The factory oil pressure guage is really a dummy light, it either shows normal oil pressure or none at all. If this is indeed correct, then I should be chasing down a electrical problem and not a oil problem, correct?

B) The horriable tapping noise could be caused by a broken stud on the exaust manafold, but if that was the case the tapping noise would NOT go away when the car warmed up correct?

C) something to clean out the oil passages in the engine could help, but what can I use? One post mention "engine purge" while others have recomended oil for desiel trucks?!? (and if so, any particular brand will meet the specs of this gas engine and not hurt it?).

D) Can I cause any more harm by driving the car the way it is. If it indeed is a lifter not working (like I think it is), does that mean I have a valve that is not working. If that is the case, won't that mean the engine will self destruct (piston + valve = horriable death)

 

My F-150 had 2 broken studs on the exhaust manifold and the tapping would go away when the engine warmed up.