99 4Runner 2.7L - 0 compression on cylinders 1 & 3 - possible causes? *Now with pics*

[iancbf32]

99 4Runner 2.7L - 0 compression on cylinders 1 & 3 - possible causes? *Now with pics*

Long story short, picked up a 99 4Runner with 95k miles for super cheap, with the knowledge that it wasn't 100%. Previous owner says "something in the transmission broke" (broken driveshaft ujoint and slip yoke) and they parked it. Truck sat for about a year before I bought it.

After getting it towed to my house, I start wrenching on it. After draining the gas tank and putting fresh gas in, I'm greeted with really tough starting, super rough idle, and foot-to-the-floor max revs of about 3k. On the plus-side, there is no smoke and there are no nasty noises, grinding, etc that I can hear.

OBDII scanner shows random misfires and misfires across different cylinders, so I change the plugs, wires, and coil packs with the same result. At this point, I run a compression test that shows ~170 psi on cylinders 2 & 4, but 0 psi on 1 & 3. 0 psi, as in the needle doesn't even move.

Visually - looking down the spark plug hole, all pistons look the same (black). There is no apparent scarring or metallic damage to the top of the piston (rules out dropped valves).

Any ideas on where to look next? Intuition says that valves must be staying open, that's the only reason I'd have 0psi compression in 2 cylinders that aren't next to each other. So, my plan now is to pull off the valve cover to see if the camshaft lobes look ok, or severely mal-adjusted valves, etc. Assuming that all looks ok, whats next?

Thanks for any suggestions or help!

 

[octanejunkie]

Other than valves (cam) either cracked head, blown rings, broken rods (that would probably freeze the crank)

Is there any coolant/oil contamination in either direction?

Have you verified all pistons are moving?

 

[iancbf32]

Other than valves (cam) either cracked head, blown rings, broken rods (that would probably freeze the crank)

Is there any coolant/oil contamination in either direction?

Have you verified all pistons are moving?

I put a long metal (aluminum) rod down the spark plug hole on affected cylinders and verified that they are, indeed, moving as expected. I see no oil in the coolant, nor coolant in the oil.

 

[phattyduck]

The 3rz cams are right over the buckets, so no rockers to come loose or anything. Maybe some bent or burnt valves? Its gotta be a pretty big hole to get 0 compression.

-Charlie

 

[JayRolla]

Have you done leak down test.

 

[iancbf32]

Any known issues with valve springs? Just trying to think of possible things to look for when I get the valve cover off tomorrow.

 

[T4R2014]

The 3RZ loves to burn exhaust valves.

 

[Scramble]

If the exhaust manifold has had a crack for a while (pretty common) you'll burn the exhaust valves. Also if the PO overheated it it could cause headgasket failure.

 

[T4R2014]

If the exhaust manifold has had a crack for a while (pretty common) you'll burn the exhaust valves. Also if the PO overheated it it could cause headgasket failure.

I was always interested in why this was the cause. Tons of 4.7L V8 powered Toyotas suffer from cracked manifolds yet never burn exhaust valves like that.

 

[RonJR]

If it sat that long, a couple of valves could be stuck open. Since I believe that engine is a non-interference engine, the valves could remain open with no other damaging effects. Pull the valve cover and see what is moving (and what's not) when you turn the engine over. A long-handled ratchet on the crank bolt will allow you to turn it over slowly and observe carefully.

 

[iancbf32]

Well, I found the reason for 0 compression. Note the stuck lifters/valves in the red squares. Any ideas on how much this will cost to fix? Should I just buy a new head for ~$600?

Cylinder 1

Cylinder 3

 

[iancbf32]

How does that even happen? How does only 1 valve in each cylinder get stuck open?

 

[octanejunkie]

How does that even happen? How does only 1 valve in each cylinder get stuck open?

Bent/broken valve or valve spring issue

Sent from my Nexus 5X using Tapatalk

 

[Kanoe]

Not very clean in there for a low mileage unit.

I'm guessing the PO was not a big fan of maintenance. Some people don't deserve to own a Toyota.

 

[gamefreakgc]

That oil up top is as black as night.

If you are industrius, you could replace the valve springs. If not... get a used head off a junker and make sure it's in spec and put it on.

 

[iancbf32]

Not very clean in there for a low mileage unit.

I'm guessing the PO was not a big fan of maintenance. Some people don't deserve to own a Toyota.

Well, It may not be pristine oil, but there's no sludge to speak of, just dark. However, that doesn't totally explain the stuck valves.

I just tried giving them some moderate taps with a brass punch to see if they'll budge, and they're going nowhere.


Is the next step pulling off the exhaust camshaft and trying to remove the cups? Maybe the valve springs are broken?


Is a brand new head from Autozone/Oreillys a viable option at this point?

 

[Scramble]

Well, It may not be pristine oil, but there's no sludge to speak of, just dark. However, that doesn't totally explain the stuck valves.

I just tried giving them some moderate taps with a brass punch to see if they'll budge, and they're going nowhere.


Is the next step pulling off the exhaust camshaft and trying to remove the cups? Maybe the valve springs are broken?


Is a brand new head from Autozone/Oreillys a viable option at this point?

I would not go aftermarket with a Toyota engine. No sludge is good. The 3RZ revs higher than the the 5VZ, my oil is black on every 3k oil change. On my manual I switch gears at 3k rpm, If I'm accelerating in a hurry I switch at 4k. My engine was rebuilt though so my engine (piston rings etc) might not have the tight tolerances that came from the factory.

 

[gamefreakgc]

Well, It may not be pristine oil, but there's no sludge to speak of, just dark. However, that doesn't totally explain the stuck valves.

I just tried giving them some moderate taps with a brass punch to see if they'll budge, and they're going nowhere.


Is the next step pulling off the exhaust camshaft and trying to remove the cups? Maybe the valve springs are broken?


Is a brand new head from Autozone/Oreillys a viable option at this point?

Toyota heads are reliable, I still think a used head will not only be cheaper but just as good and you won't have to piece it all back together.

 

[octanejunkie]

Those pics are confusing, I don't see a gap between the cam lobes and spring caps in the red-squared areas - perhaps it's a bad angle

If the valves are stuck open, the springs would have to be all the way collapsed into the seats, and there would be a gap between the cam's base lobe (valve closed position) and the spring cap.

If the valves are stuck in any position other than fully open (springs totally collapsed) then I would imagine there had to have been damage to the cam lobes of the same valve (cam wiped out) and you would probably want to replace the head.

 

[Trojan4x4]

A tip for next time. If showing low compression, pour some oil in and retest. If you got a piston related problem, the oil will seal it and the compressor will go up. If the compression stays the same, most likely a head problem.