Camshaft or tappet loud rattle and power loss

I have a 2.7vvti engine with hydraulic lifters, the intake cam rattles like crazy sounds like very loose valve clearances. There is also a loss of power. From cold to hot and from idle upwards, though as I rev it up it gets louder of course. The engine was very dirty so I put in new slightly higher viscosity engine oil n added Wynns Charge but that made no difference at-all, cleaned out the oil pressure regulator on the oil pump. Took off the timing cover and opened n inspected the oil pump, no wear to speak of n I cleaned out the tensioner too. Changed the lifters all round, 16 of them, no change. Then pulled the intake cam, stripped and cleaned out vvt unit, released it and reassembled.... arrrrgh! No change... I confess to be at a loss. The cams are in mint condition, no wear to feel, can only see where the rockers have been running. All the rockers are rolling free and unworn I checked each one in turrn, the lifters are snug in their bores, nothing floppy
I also had the vvt solenoid out and tested it's function with 12 volts, seems ok, the plunger clicks up n down and doesn't seem to sticking and so far this is the one item I did not wash clean. Could it be a computer glitch where the vvt solenoid is either not working or is working incorrectly/erratically? I'm open to anything here. 4 days off n on and I might as well have not lifted a spanner.... Just can't help feeling I've left something out though none of my buddies see it either. One thing we don't have access to out here right now is a diagnostics computer, we took it to the nearest Toyota dealer workshop, acted all dumb, n they said it's a bucket shim.... ummm, DUH! It's hydraulic

 

I would just drive it

 

I would do that Mr Cookie, but the noise is too loud. I will try uploading the sound file or take a video
So far the closest-to-what-I-think-correct advice has been the vvt unit but I can't just fit a new one coz it's simply too costly if it proves to not be the answer...

 

Flat cam , lost a lobe !!!

 

What viscosity oil are you using?

 

Cams are like new as I wrote. I have tried 2 different oils since I started on this problem, 20w50 & 15w40 which is in there now. When it started the noise it had Toyota's branded oil which is 10w30
The valve lifters are new, fitting them had no effect

 

I am about to reset the vvt.... again and more closely check the little valve inside it, I will also remove the vvt solenoid... again so I can clean it and I am also going to hunt for a vvt oil filter. I know some Toyota engines have them I just don't know if the 2TR has one.
I also tried stepping up the oil pressure a bit by spacing the oil pump relief valve spring, also no effect. The cam journals are also like new, no significant wear visible. So I don't think it's:
Valve lifters
Engine Oil pressure
Oil viscosity
Cam wear
VVT unit in itself (looked good inside)
VVT solenoid (but maybe ECU?)

Other than that, no idea... and I hate admitting defeat, it's just an engine, I'm never one to quit easily

 

how many miles? could be bad gasoline? low oil pressure would cause the lifters not to pump up all the way is all I can think of...I dont know about the vvt computer stuff.

 

About 400 000 kilos. We had the motor put and did a basic rebuild in March, we think now that it has to do with the cylinder head. These motors are notoriously finicky.... umm, temperamental when it comes to.Head skimming, warpage etc. So we're looking a complete head, with valves, rockers, lifters, cams, but unit so all we need to do it put in a new head gasket, drop the head on and.... well, let's see what happens
Oil pressure at idle cold is close to 4.7/4.8 bars. VVT solenoid works eeeesh! I can scream, 2 weeks of this and no solution... yet. We seem to have exhausted all options/possibilities, so now the focus is the head. What I might do before a head swap is to do an.intake cam swap complete with the vvt unit n see what happens, failing that it's off with it's head!
Thank you all of you who have tried to help, it frustrating for us here, but we will persist and we will solve it, then I will let you all know what the cause was. One thing is very obvious.... Keep that engine oil CLEAN!

 

Update?! How did it all turn out for the OP?? I ask because I'm here searching for answers to the very same/similar issue. I'm curious to know how your project progressed and what the underlying cause was...

In the meantime, I'm still tinkering away with many of the same things you have mentioned in an effort to alleviate the loud ticking/drop in power when under load, amongst other symptom issues.

My question I have at the moment for anyone else bearing any knowledge in this line of thinking is in regards to the VVT solenoid. what is the proper voltage reading to be coming from the wiring harness end which plugs into the solenoid measured with it unplugged and the key in the "On" position?
Or more simply stated, what is the operating voltage of the VVT solenoid?
I'm trying to check an verify the wires leading up to my VVT solenoid are in fact delivering enough volts to properly power the solenoid. Upon checking it (by the method described above) it measured at only 1.5V which seemed quite low to me.

Any idea as to an exact voltage or a voltage range which the truck should be supplying to power the VVT solenoid?