chicomacattack

Sounds like a wrx. And compression is 240 230 240 and cylinder 4 is 120.any ideas what it could b3. Or how to doagnose the problem further. And how to fix it

JUSTINTHECOASTIE

Sounds like a bent valve(s) get a leakdown test done

PdxPartsCo

anything significant recently happen that could cause this?

chicomacattack

Well it would jerk every now and then with bad gas or when i went low on gas. The day before i almost ran it empty and the next day it jerked a few the cel came on and started flashing and started shaking. Obd said misfire in cylinder 4. I checked the coils and spark plugs and injectors all are good. What will the leak down test tell me?

jeffbrig

That the cylinder is not air tight. Nothing that you don't already know from the compression test, IMO.

Slowcrash_101

Leakdown test is best on these cars, that way you don't have to remove hot spark plugs from the aluminum head. It will tell you whether it's exhaust valves intake valves or rings.

06Estukay

Agree with Slowcrash. Do a leakdown, and report back.

If it's a valve, pull the head. If it's a ring, the whole engine has to come out. Big difference between those two jobs, so finding out if the problem is top or bottom end is key.

Listen for air escaping at:

-Intake (indicates intake valve(s))
-Exhaust (indicates exhaust valve(s))
-Oil dipstick hole (indicates piston ring(s))

chicomacattack

So i took it to a shop qnd now there trying to tell me that my tps is whats causing low compression im pretty bs ure there full of it

DeeKay

i call bs. throttle position isn't relevant to cylinder compression.

PixelJunkie94

All great points! I'm not sure if you have attempted a wet (oiled) compression test. That will speak volumes about your rings and doesn't require any additional equipment that a compression test requires at this point. With the "wet" test, you should see your number go up a bit, if it jumps up past 160 I would def blame rings. However, rings are unlikely as they generally wear down similarly with age/miles. I'm thinking you have a specific mechanical failure such as valves. TPS is not causing your low compression.

Chris Brewer