compression test

[microgalant]

I have a 4g64 engine with 4g63 head wiseco piston 9:1.1,.20 over cometic head gasket, eagle rods.
Engine was built last year sept.
This year i put the turbo on, went dyno last week, and today i decided to do a compression test just to see if everything is ok.
1)120,2)120,3)125,4)125
Is that ok??

[WarmAndSCSI]

How many times did you let it crank when doing an individual cylinder? Those numbers are below the acceptable threshold of 125-130 PSI. That could be because you didn't crank it enough.

You're really looking for numbers ranging from 160-170 PSI with 9:1 compression.

[microgalant]

i'm i think 4 time,but wait, do i have to get all four spark plugs out?
and btw my battery was a little weak

[laxinwarrior]

I say try it again but this time charge up your battery first just to be sure and don't forget to block open the throttle body or else it will skew your numbers as well.

[tom04841]

The proper way to do a compression test is to:
1. Get car to operating temp
2. Remove all spark plugs
3. Remove fuse for injectors
4. Block open throttle
5. Crank until the gauge stops going up
6. Repeat on the other three cylinders

As a side note, a weak battery WILL result in lower numbers. Make sure battery is fully charged.

[microgalant]

I have a problem,either with the battery or the altenator.
But i think the battery doesn't charge sufficient.
My car start too weak

[eksz]

If your battery won't turn the engine over you can use a battery charger that has a "boost" or "starting" mode. I am not sure if Walmart is in Aruba but if so you can find an affordable charger there. Set the switch and it jumps up the power being supplied to your car so that even if you have a dead battery/bad alternator it will still power up the starter enough to turn the engine over for a compression test. jjj

[WarmAndSCSI]

Unless you have a battery charger with a 200 A "boost" mode, it's not going to help turn the engine over fast enough for a good compression test.

[eksz]

Just checked my battery charger and the boost setting is only 100 amps. On my stock 2.4L 4G64, it will easily spin the starter/engine. FYI: It is an Everstart 100

[WarmAndSCSI]

Does is spin the engine as fast as the starter does when it's healthy? Probably not.

[eksz]

You know I can't say for sure as it has been a month or so when I did it. It did sping it fast enough for ithe engine to start despite the battery being stone cold dead and the prevailing outside temps being in the mid 20's (F).

[WarmAndSCSI]

You won't see good compression numbers unless you get the engine cranking at the correct RPM (250-400 RPM).

[4-G-rim]

Your compression numbers are really low...those numbers are out of spec compression numbers for a stock 4g63, so its even lower for your built motor. Like what the others are suggesting you will need a healthy battery to crank the car up a good 5x's to get a good compression reading. You also want to make sure it holds compression too.

After you check the compression ratio of all the cylinders and they all check out. You want to take the cylinder that has the lowest comp reading and do the compression test again on that cylinder. Take the reading and keep the tester hooked up for a hour or so and check if the compression has gone down.

My stock 4G64 with 130,000 original miles has 210 compression all across the board and holds too. Your compression numbers should be around the 180-200 for your motor. ( I am assuming it should be higher than a stock 4G63)

How much ft lbs of torque did you torque your head? Did you retorque it after the engine was running at operating temp for a bit?

[WarmAndSCSI]

Just a few comments of my own:

The compression of a built motor is going to be lower if you put in lower-compression-ratio pistons.

The compression tester has a check valve, if the compression went down after an hour, it's because the check valve leaked some air back into the cylinder.

I agree with you about 180 PSI, but he's not going to see 200 PSI cranking compression with relatively low compression pistons.

No Mitsubishi head requires retorquing after reaching operating temperature - the most you have to do is retorque once during assembly. A warped or poor-sealing head would be holding hardly any compression at all, not 120+ PSI.

[microgalant]

ok guys, i went today, check the compression again, like you guys told me to do.
The results, piston 1-150,piston 2-150,piston 3-175,piston 4-150
I don't know why piston 3 is 175

[WarmAndSCSI]

Bad carbon buildup can cause a cylinder to read high or the other 3 could be sealing poorly.