Hi,a few weeks ago my engine (4.6) lost all oil pressure,after getting the truck home on a trailer i started it up,it had pressure for about 45 seconds,shut it off started it again,and again the same thing,so assuming it was a bad pump i replaced it ,i just got it back together started it up and it ran good for about 4 minutes then it droped all pressure again,when i removed the timing cover i found one of my timing chain guides had broken into about 5 pieces i recovered most of the pieces,but some had gotten ground up, do you think that some of this ground up guide could have clogged up the screen on the pick up tube? Is there anything elese that could cause the engine to lose pressure then when you shut the engine off and immediately start it back up, it has pressure for another 4 or 5 minutes then drops again? I also
changed the timing chains, guides, tensioner, oil and filter...

Thanks in advance for any help......
Jerry

 

I would replace the oil pump again, and make for sure that i got EVERY single nit pick thing right

could be a bad relief valve. if your truck has a rev limiter, i would hold the pedal to the floor when the oil pressure drops, and that might "make it snap back" hope this helps

 

Did you clean out the pick up screen? Often when the screen gets cloged by debris and you shut the engine off the debris falls to the bottom of the pan. When you start the engine up the debris gets sucked back into the screen and clogs it all over again. Pull the oil pan and flush it out along with the pick up tube.

JMC

 

My question is how are you making the determination that the oil pressure is dropping?

 

Is the chain guide tensioned by oil pressure? if the guide broke it could be the reason for the presure drop. Just a thought as I have not had to get into that area before.

 

run the engine till oil pressure drops, then immediatly drain the oil after shutting the engine off. then stick a magnet inside the drain hole, and replace the magnet. the magnet will stick to the drain plug, and 3000 miles later, your problem will be solved

 

the gauge drops all the way down,and the engine starts to rattle,and knock

 

yes you are correct,but i replaced the guides,tensioners,chains,and crank gears,while i was that deep,i didn't want to have to go in again,i hope i don't have to anyway.

 

JMC you are the man it was indeed debris on the screen and in the pan,and alot of it,also found a few bad rod bearings,although the crank was not in the best of shape (not to bad) i went ahead and replaced all the bearings while i was there,hoping that will get me through the last 5 payments,and the rebuild of my other truck,then the engine will come out for a total rebuild,and passed on to my 16 yr old son,who i'm sure will be the final death of the truck...HEY but we were all 16 yr old boys at one time.

thanks again JMC,and all the others who replied,
Jerry