How hard is it to do a compression test and how long does it take? What exactly do i need to do?

Thanks

1.Buy a comp. tester
2.warm engine to normal operating temp.
3.pull all plugs
4.unplug ignition coil
5.install tester in 1 cylinder
6.crank engine with throttle wide open for about 4-5 seconds
7. write down results.
8.repeat steps 5-7 for each other cylinder.
9. re-install plugs
10. plug ignition coil back in.
11. start car to recharge battery.

Generally pulling the plugs involves removing the washer res. and perhaps the intake tubing(stock).

Good luck.

p.s. if I missed anything I'm sure we'll hear about it.

Good write up. Try to have one person checking the comp. while another turns the key.

Nick

Unplug ignition coil?? Aren't the coil packs attached to each plug??
Crank at WOT? Gas pedal down & crank the engine??

Unplug ignition coil?? Aren't the coil packs attached to each plug??
Crank at WOT? Gas pedal down & crank the engine??

On an 02/03/04/05 wrx, yes you have coil on plug. You'll find that they get unplugged when the spark plugs are removed. On an 00' rs, there is a coil pack

And,

Yes, you need to have the throttle wide open during the test.

Was there anything else?

I've done leakdown and compression tests before. Fully aware of how you do it. But, how do you do it on a 'drive by wire' STI? How do you get the throttle to be wide open?

t

It is the same for the STi. I did it a few weeks ago to my STi.

Nick

I've done leakdown and compression tests before. Fully aware of how you do it. But, how do you do it on a 'drive by wire' STI? How do you get the throttle to be wide open?

t
Hold your foot on the gas ;)

I assume that most people don't remove the battery when changing plugs then? Or do you remove the battery, pull the plugs and reinstall for the test? Just curious...

Also, shouldn't there be a way to prevent fuel from entering the cylinders during this test? Will fuel in the cylinders skew the results?


Good thread so far...I've been wanting to do a compression test for awhile now.

I assume that most people don't remove the battery when changing plugs then? Or do you remove the battery, pull the plugs and reinstall for the test? Just curious...

Also, shouldn't there be a way to prevent fuel from entering the cylinders during this test? Will fuel in the cylinders skew the results?


Good thread so far...I've been wanting to do a compression test for awhile now.
Fuel in the cylinders shouldn't have any effect, just for kicks I've done a compression test with fuel and with out fuel, and there was no difference at all. I couldn't find the fuel pump fuse, so I just unplugged the injectors to stop the fuel.
Since we're talkinga about compression, here are my results from last week:
cyl 1: 175psi
cyl 2: 176psi
cyl 3: 175psi
cyl 4: 178psi

Nice results! And thanks for the reply...now I just have to find the time to do it.