Failed compression test - What to do next?

[recoil]

Hey guys, my skyline story becomes more of a horror story every day.

I did a compression and leak down test, here are the results:

Compression:
Cylinder# - PSI
1 - 157
2 - 157
3 - 155
4 - 156
5 - 128
6 - 145

Leakdown:
Cylinder# - PSI
1 - 160
2 - 159
3 - 160
4 - 161
5 - 131
6 - 147



Soo.. What's my next step? I guess I obviously have to pull the motor.

Is there any easy way to tell what needs to be done to fix the compression? I have never had to re-build a motor before. I can't believe I bought the f'in car like this, I wish I knew then how to check the compression.

[Supraclean]

Was this done on a warm engine? I mean that's low in number 5 but how's it run?

[DarkCaporaL]

^

Are you having specific issues? If the engine still runs, and this is just a street car, I would just keep running it until it blows. It could still last quite a while.

Looks like a classic case of leaning out on cylinders 5-6.

[RWD_GTR]

my motor has 130psi across. Im driving it. just gonna crank the boost

[MarusGTR]

I'd be freaking out too, but lets be honest, it's probably nothing to worry about right now, especially if it's on stock boost. If there's no smoke and it's smooth keep going at it, just make periodical tests (each season).

BTW, if coolant levels are ok, there's no coolant contamination, there's no blowby and no smoke there's seriously no reason to panic. It could be a valvework problem.

[Bugsly17]

Cylinders must be within 20% of eachother. Too lazy to do the math. But those results do not look too bad to me. And I'll bet it was not done correctly anyway.

[recoil]

I fouled 5/6 plugs in four idles for 10 minutes each, not even driving it once, car runs extremely rich. The motor shuts off around 5k rpm's under wot, almost stalls after coming to a quick stop, assume that's due to vta bov which I am going to try & recirc.

Car is slow to boost, may have a vacuum leak, no clue what is causing these problems.

You don't think it would be a good idea to look now before it blows? I read somewhere 150+ PSI in all cylinders was important.

Cylinders must be within 20% of eachother. Too lazy to do the math. But those results do not look too bad to me. And I'll bet it was not done correctly anyway.

I followed the instructions in the shop manual. I pulled the fuel fuse until engine shut off after warming up and cranked to make sure. Took everything out, tested all cylinders cranking until max psi was read. Put 3 drops of oil in each cylinder and tried again.

[amnash]

good idea to go over whole engine with an un lit propane torch to check for vacuum leaks.

[DarkCaporaL]

Yeah I'd start with the basic and easy stuff first.

What do you mean by car "shuts off" around 5k RPM? Like hitting a wall and it doesn't have any power?

Check for vacuum leaks and check your MAF.

Cylinders must be within 20% of eachother. Too lazy to do the math. But those results do not look too bad to me. And I'll bet it was not done correctly anyway.

He's getting close to the limit, but he's still within working range where the motor should still run, unless there's an internal failure somewhere.

[recoil]

I've cleaned the mafs, but I've never actually tested them. I can almost guarantee I have a vacuum leak... I'll have to track it down.

[Bruizer]

Service manual says 14psi between cylinders or more needs replacement.

If you're doing your compression test when warm and wot, then it's the right readings. Put a teaspoon on oil in the plug hole and see if that helps. If so, it's the rings. If not, most likely a valve.

Nothing wrong with low comp on a stock car. Just drive it. If you were dropping Money (not talking about $100 boost controllers either) into it thouth I'd rebuild it. Otherwise it could be fine for a long time. Do lots of oil changes.

[recoil]

I will re-do with a tea spoon of oil.

Any idea why I fouled 5/6 plugs idling for a total of maybe 30 minutes?

The motor was extremely hot, maybe I have to go 1 heat range colder?

If I have more chance of a lot going wrong without fixing it now such as bad pistons etc, I might as well just re-build it now rather then spend extra money for not fixing what was wrong in the first place. I do plan on dropping a lot of money on the car, but the a lot of money takes a long time to build up so there are no immediate plans but with the mods I have I feel I could push close to 400hp with good compression.

[Bugsly17]

Buddy, run the car.

I just compression tested my rb26-
1. 5 psi
2. 10 psi
3. 5 psi
4. 20 psi
5. 25 psi
6. 25 psi

[DarkCaporaL]

^^ hahaha I can see why you hate Skylines

[Bruizer]

Buddy, run the car.

I just impression tested my rb26-
1. 5 psi
2. 10 psi
3. 5 psi
4. 20 psi
5. 25 psi
6. 25 psi

you either did something wrong, make like 0 power or you're timing assembly is way out