Did a little compression check this morning and the results are in:

#1 - 165
#2 - 166
#3 - 168
#4 - 165

Service manual indicates ideal pressure is 163lbs.
I love my car.

 

Great a clean bill of health now for some big powa!

 

does your higher compression just mean you have a strong motor?

 

hellifIknow

prolly just means I didn't know what I was doing when I ran the test. The most important thing is that I'm right around the target range and all cylinders are within' 3lbs of each other.

 

how do you do your own compression test? I am just curious. It's good to hear that you are in good shape and your motor is healthy!

 

As long as you had WOT, the engine was warm and you rotated the engine on the starter a least four times per cylinder you did it correctly.....
I have seen cylinder variances from as high as 175psi to as low as 140psi, however I have not tested a single evo yet that has not been within the 14psi specified difference between cylinders...

 

so can anyone plz explain how to do a compression check?

Thanks

 

I made so many mistakes, I might do it again.
Using the Evo Tech manual as a reference, I made the following mistakes:
1. Engine was cold
2. Crank angle sensor clip was not disconnected (which I believe is meant to disable the injectors)
3. I pulled only one plug at a time and then reinserted it before moving on to the next cylinder.

 

when I did mine it was cyl. 1 170 cyl. 2 170 cyl. 3 166 cyl. 4 171

I am pretty sure those are good numbers.

 

This will lower numbers due to heat expansion of pistons within sleeves usually raises compression.

You are correct, by not disabling the injectors you spray fuel into the cylinder. This in turn degrades the oil buildup on the walls (the buildup helps compression) and in extreme cases can cause the rings to wash out causing total loss of compression. (this takes a LOT of fuel, obviously this didn't happen to you, you still got good numbers)

Slows the cranking speed of the engine since it has to compress the gasses in those cylinders, again, lowering numbers...

So if you got ~166 doing all these things wrong, you're probably one of the people in the 175 club. Congrats

- Steve

 

Superhatch,
You ROCK! Thanks for the analysis! I just got done reading that our Evo is #1 of all time in Sport Compact Car magazine, so I was already feeling great. Now I read this and feel even better.

 

I forgot to disable the crank angle sensor and also did the test when the motor had only been run for 5 seconds. It read 150 across the board, should I buy the car? Is the compression good enough?

 

Disable spark/fuel while peforming test via fuse for ECU or CAS.
All spark plugs should be out.
WOT while cranking.
Only 4 rotation of crankshaft should be read.
Make sure the battery is fully charged. Slow cranking would reveal lower readings.

Nice healthy motor there Smog.

 

Mine did 180 on all 4 and i just checked it last week. As long as you are within 10~20 psi from each piston you are ok.

 

From the shop manual:

COMPRESSION PRESSURE CHECK M1111002600421

1. Before inspection, check that the engine oil, starter and
battery are normal. Also, set the vehicle to the following
conditions:

• Engine coolant temperature: 80 − 95°C (176 − 203°F)
• Lights, and all accessories: OFF
• Transaxle: Neutral

2. Disconnect the spark plug cables.

3. Remove all of the spark plugs.

4. Disconnect the crankshaft position sensor connector.
NOTE: Doing this will prevent the engine control module
from carrying out ignition and fuel injection.

WARNING
Keep your distance from the spark plug hole when
cranking. Oil, fuel, etc., may spray out from the spark
plug hole and may cause serious injury.

5. Cover the spark plug holes with a shop towel etc. Crank the
engine for a few seconds to clear debris from a round the
spark plug holes. After the engine has been cranked, check
for foreign material adhering to the shop towel.

6. Install the compression gauge to one of the spark plug
holes.

7. Crank the engine with the throttle valve fully open and
measure the compression pressure.
Standard value (at engine speed of 250 r/min): 1,128
kPa (163 psi)
Minimum limit (at engine speed of 250 r/min): 951 kPa
(138 psi)

8. Measure the compression pressure for all the cylinders, and
check that the pressure differences of the cylinders are
below the limit.
Limit: 98 kPa (14 psi)

9. If there is a cylinder with compression or a compression
difference that is outside the limit, pour a small amount of
engine oil through the spark plug hole, and repeat the
operations in steps 6 to 8.

(1) If the compression increases after oil is added, the cause
of the malfunction is a worn or damaged piston ring
and/or cylinder inner surface.

(2) If the compression does not rise after oil is added, the
cause is a burnt or defective valve seat, or pressure is
leaking from the gasket.

10.Connect the crankshaft position sensor connector.

11.Install the spark plugs and spark plug cables.

12.Use the scan tool to erase the diagnostic trouble codes.

NOTE: This will erase the diagnostic trouble code resulting
from the crankshaft position sensor connector being discon-
nected.

I got 175 on all.

Should I put this in the how-to section?