Compression Test

[wiccanferret]

What's the easiest and least expensive, yet definitive way to test compression? I'm wanting to see if my 223k mile 3100 is worth putting more money into or if I should just save up for a new longblock. Is there anything else I should look for? It doesn't smoke at all and performs well.

[Homer]

All the cylinders should be within 10% of each other, thats the easiest way to figure out if you have a problem.

[wiccanferret]

All the cylinders should be within 10% of each other, thats the easiest way to figure out if you have a problem.

Ok. That's the end product. I guess working backwards is better than not at all. What I need to know is where to get a compression tester, how much should I expect to pay, how do I use it, etc etc...

[pontiac92gp]

About $30 - $50 for a compression tester. Any parts store would have one .. AutoZone, PartsAmerica, etc .

To test, take out one spark plug at a time, screw in compression gauge and crank.

I found it best to grab a piece of paper and draw 6 circles (3x2), one for each cylinder, and label the circle with a cylinder number. As you check the compression, just write it down next to it. If this is confusing .. then forget I mentioned it

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[Anonymous]

Oh, make sure you pull the fuse for injectors & ECM or something so it doesn't start up. I believe the Haynes manual says to let it turn over (as in, bump the needle on the gauge) 7 times then stop & read the results.

[RLJ]

You should disable the fuel and ignition systems before you do it though. Simply pull the ECM/fuel pump fuse and the DIS fuse.
Crank the engine over for 6-7 compression strokes and watch the guage. The compression should build up quickly. If it doesn't something is worn. Then try squirting some oil into the cylinder and try it again. If the compression jumps up, the rings are probably worn. If not, it's probably the valves.

[wiccanferret]

You should disable the fuel and ignition systems before you do it though. Simply pull the ECM/fuel pump fuse and the DIS fuse.
Crank the engine over for 6-7 compression strokes and watch the guage. The compression should build up quickly. If it doesn't something is worn. Then try squirting some oil into the cylinder and try it again. If the compression jumps up, the rings are probably worn. If not, it's probably the valves.

If it's either I'll probably just leave it be and start saving for the 3400 swap. Thank you for your help guys!

[v6h.o.]

To test, take out one spark plug at a time, screw in compression gauge and crank.

the proper way to do a compression test is remove All spark plugs, and have the throttle body open.

i usually take a screwdriver and stick it in the throttle bore to hold the t.b. open so i dont forget, it will make a difference.

also pull the fuel pump relay or fuse, to kill the fuel.

[Homer]

I bought my compression tester from sears, its an actron, I like it and it cost like $40. To add on to "the proper way" make sure put the spark plug wires some where you won't be able to get a nice poke from the DIS.

[Cliff8928]

I bought my compression tester from sears, its an actron, I like it and it cost like $40. To add on to "the proper way" make sure put the spark plug wires some where you won't be able to get a nice poke from the DIS.

Or you could just unplug the 2-wire connector on the ignition module (which supplies the power and ground)

Cliff Scott
89 BerettaGT
89 Volvo740