Taco is officially tostada! Diagnosis revealed! Never would of thunk it. Not on this bottom end.

Just did the head gaskets on my 2012 tostada 3 months ago. She'd been running great no issues. On my way home from a two hour round trip this Saturday I pulled off the highway, came to a stop on the offramp(traffic light) and so did my truck, just died. Tried to restart and got some horrific motor noise. Kinda like a bolt was flying around in the bottom end. Towed it home. Ripped the intake and valve covers off, inspected all cylinders and valves with scope and all look good. Compression test. Two rear cylinders on each bank have high compression while the remaining four have ok but lower than I like compression. Looked in the timing cover, looks fine although haven't pulled that yet. Drained oil and inspected, no metal or foreign objects and still making a nasty clacking noise from the back of the motor, almost sounds like it's coming from the tranny. I'm at a loss... Anyone got any ideas? Bout to give up on her. No codes no nothing. I'm not an expert but a bit more advanced than the average joe and I have a Toyota mechanic helping and he is very frustrated. Bout to put it back together and run it to diagnose despite the nasty clacking. Just thought I'd ask here and see if I could have some knowledge bestowed upon me. Thank you in advance.

 

Plus checked VVT solenoids and I'm about to blow some compressed air into the cam to see if that thingamajiger at the end is working? I'm out of ideas after that. Anything helps, even derogatory statements if that's what you're into. I can take the abuse!

 

like what kind of compression numbers are we talking about?
It almost sounds like a timing component let loose. ?

 

That was my immediate thought because I had just pulled the heads had them resurfaced and the valves done but the timing components all check out. Valves are operating fine or they are not bent at least. Chain has tension, tensioners are there, no chainsaw noise coming from the timing cover. Just a nasty clack from the back of the motor. Looked in all the cylinders with a scope and they look fine except one is a little dirty on top and that's one with the high compression!? Trying to test the vvt with air pressure but have no idea what I'm doing. One other odd thing is that before I tore her back down I started it, no engine noise but lost rpm and died immediately. Tried it again and it started but with the hideous clacking noise nack. I've had a stethoscope on it, running the motor with the starter and still cannot pinpoint where the hell the noise is at. I'm putting it back together and I'm gonna run the damn thing til I figure it out or something catastrophic happens!

 

Starter noise? Maybe it’s not disengaging.
Another thought is something in the exhaust, either a loose pipe, cat. etc.
Motor mount…

some things to check at least

 

Cracked flexplate or broken flywheel bolt if manual

Both make noises

 

Spun rod bearing maybe. I’ve seen them clack like a crazy lady then all of sudden just go quiet then go crazy again.

 

I thought cracked flex plate in automatic was only 3rd gen 4Runners
Haven’t seen a cracked flywheel

doesn’t hurt to do a leakdown test but might not find anything

right now it sounds like a bottom end rod knock having to do with the connection area of the rods and crankshaft and may also not be too involved to check.

supposedly pulling the upper oil pan is not that hard, if it’s required to gain access to the bottom end and see if there is any play at the lower back of the motor.

As well as front/rear movement of the crank such as if it used thrust bearings that developed an issue. Easiest way to check that is probably pry bar wiggling the crank pulley to see if it rocks back and forth or not.

supposedly the motor can still run with the trans pulled out. To see if it’s the motor or trans. But that’s not exactly a common easy diagnostic step.

 

This what i was thinking. However, with all of that head work, I would be thinking that compressions would be more consistent. Moved my feeling to something done wrong with the cam timing or problems in the hydraulic cam rotator up front. This would explain the compressions, but not necessarily the clanking.

 

Thanks for the feed back. I was leaning towards the hydraulic cam rotator just don't know how to test it? And now I'm lil worried about a rod bearing! I am pretty hard on the girl. I've heard the bottom ends don't let go on these 4.0's unless you got some asshole like me hauling a bunch of weight and not letting up. Not to mention I've got 279,000+ miles on her. Was hoping to get 300k before major motor work.Well shit.. looks like ill be ripping the oil pan pan off to check the rods too. Really do appreciate all the ideas gentlemen. I'll report back when I get this thing figured out.

 

Is there a way to test the rotator? I was thinking of pulling one of the keepers and blowing some air into the oil port to see if the thing was actuating but don't really know if that's kosher or if I can screw up a perfectly good part by doing so?

 

180 on the back two, 150 on the front 4. If that makes sense. When I say back two I am describing left back and right back and so on.

 

Well that certainly would suck but is the best theory Ive heard so far on where the hell this noise is coming from. Thanks for your input.

 

I like to think pretty good with a wrench but the last time I pulled a trans I swore I'd never do it again! At least not without a lift and a trans jack! Lol I am definitely going to check the crank pulley, I'm going to run it one more time then most likely pull the pan if I don't find something else first. Thanks for all your wisfom. It is appreciated.

 

Compression can vary. Some folks say it’s fine as long as it’s in spec.

hopefully lower compression isn’t indicating a rod bearing worn or failed to the point of the piston moving down enough to have less compression.

 

Keep us posted

 

I don’t think you can use air, as the vvt solenoid has perpendicular slots for the oil flow in a round bore. So no way to hook up an air source. Generally the ecu will try to advance or retard the timing via the vvt and if the sensors don’t pick up the changes on the cps, it throws a code. So thinking they may have messed up the timing over a problem with hydraulic actuation. Getting the timing wrong would not throw codes, as the ecu does not compare cam position to crank position. It just assumes no one screwed it up.
After seeing the compression results, i am not so sure about cam timing as a cause for it. I would expect all 6 to be a bit low. If the valves were ground, that means new caps/shims and therefore possible they went too tall, preventing the valves from fully closing. A leak down compression test would tell the tale.

 

A rod bearing is only about 3/16” thick and the stroke is probably 3”+, so doubt that a missing bearing could account for a 20% reduction in compression. Not saying we don’t have a bearing issue, only that it shouldn’t account for the compression loss.

 

Well, put her back together and fired it up and holy guacamole! You want to talk about noise! I think before with the oil pressure still built up it was hiding it, and with the plugs out and zero oil pressure it was being disguised. Not 100% certain yet but I think there may be a broken valve spring in my future. Really sucks cause I just spent 2k on the heads 3 months ago when I did the head gaskets. Luckily I know the machinist and he'll make it right if that is the problem. Well better get to tearing this thing down.... Again... I want to thank all y'all for all the input. I was pretty sold on the rod bearing being the problem but it's definitely on the top end. Gonna do a leak down test to make sure and then I'll update this thing. Spring makes sense though with the intermittent sound of the death rattle. Comes on rattling, idles down then goes away, idles up(on its own) starts rattling again and idles down goes away and rinse and repeat

 

150 psi isn't great