Compression test result on a 3.4 V6 engine

Hey,

I did a compression test on my engine. It run good but I did it by curiosity.

The result: starting from the right front cylinder :

1:179 4:179
2:150 5:150
3:180 6:180

The results seems to me very symetrical, but the center cylinders have less compression ( 17% less)

Is it normal or there is a problem?

 

Per the Toyota FSM 2001

With fully open throttle, and a full charged battery to obtain at least 250 RPM on a warm engine.

5VZ-FE
174psi or higher
145psi Minimun
Difference between cylinders 15psi

I'd retest and do a leakdown, otherwise you've got 2 cylinders on their way out. The engine will run quite a ways lower yet, especially with 4 good cylinders pushing but you'll be losing some hp/mpg on those 2 eventually. I have no personal experience with those motors but from reading, 2 and 5 seem to be problem cylinders, 2 being the more prevalent.

 

The spark plug on the cylinder 2 had some burning on it... I dont know if its linked...
Thanks for the answer!

 

The engine is still good. Low compression could be from piston ring wear or a leaky valve.

 

Burnt oil on the plug, best guess is piston ring.

 

there's another test you can do, put some oil in the cylinder (coil not connected to spark plug) and do the compression test. i think if you do this, and the compression improves, you need new rings. or something like that. few beers and everything's a little fuzzy. can anyone else chime in on this?

 

or you could use chevron gas and/or system cleaners to remove potential carbon buildup on the valve seats that could be allowing compression loss.

 

Yes, if compression increases with a little oil in the cylinder its usually a sign of worn rings. Low compression could also be something as simple as valves needing adjustment.

 

Thats roughly correct. Whats incorrect is directly attributing bad rings to it, there could still be bent valve if you money shifted or the timing belt lots a tooth. Though some level of blowby is expected and designed in to allow for thermal expansion. Not offsetting the break in the engine rings during installation can cause extra blowby. Most often a lack of compression is through crack heads or a bad head gasket

 

Squirt a little oil in the 2 low cylinders & then test again, that will most always narrow it down to rings or valves (as undying said). That engine will run a long long time just like it is.

 

"there could still be bent valve if you money shifted or the timing belt lots a tooth."

3.4's are non-interference motors so a timing belt jumping wouldn't result in a bent valve.

 

Oh man.... other day a daewoo head came by my shop for rebuilding. Timing belt had broke. 8 of the 16 valves were bent. 2 intake, 6 exh. And i had to hammer the valves out just to start the whole rebuilding process. he's likely going to need new valve guides and seats. It was ugly :-( but it's still a couple hundred dollars cheaper to rebuild than to buy used.

 

Daewoo.....

 

Some timing belt engines will damage valves if the timing jumps or if the tb breaks, that's a interference motor. But the 3.4L is a non-interference motor.

 

so i did mine today out of both curiosity and boredom
from right front;
1:175 2:176
3:169 4:164
5:166 6:231

#6 ...231 is really out of spec with the rest not to mention really high so i suspect error...241543 miles.