How do i properly do a compression test?
 

i have a 93 ls motor in my hb. how do i properly do a compression test on that motor? i have a tester already. and whats the compression supposed to be?

RE: How do i properly do a compression test?
 

Forgot exactly what the number range is supposed to be.

As far as performing the test.....
1. Pull your plug wires off the plugs (remember their order....where they go)
2. Remove your spark plugs (good time to check the condition of the plugs to spot problems)
3. (OPTIONAL) Unplug your injectors (some people do but it's not necessary)
4. Screw in tester to spark plug hole #1 - have someone hold the gauge face towards you as you are going to go into the car & crank the car over for a good five seconds or more.....until the needle stops moving up....that is your compression # for that cylinder. You can do this w/o looking at the gauge. Just make sure that you crank it over for enough time for the cylinder pressure to build up in the gauge to give you an accurate reading. Record or remember the reading.
5. Remove the tester from the spark plug hole. Release the air psi from the gauge and screw into cilinder #2 and repeat step 4.
6. Do this w/ all the cylinders.
7. If you see any major differences between cylinder pressures, just do the "bad" one or ones over again to double check the numbers you first recorded.
8. Put your plugs back in and wires back on & you're done.

I know that there is an "acceptable range" as it doesn't need to be an exact number for all cylinders. You're just gonna see if there are any MAJOR differences. If so....after double checking pressure and refferencing your numbers to pinpoint the problem.....time to ask more questions......

We'll worry about that later.
Let us know how it goes.

RE: How do i properly do a compression test?
 

thanks for the detail. ill check it tommarrow.

RE: How do i properly do a compression test?
 

For the compression test, jus remove one plug wire and one plug. Remove the ECU fuse so the injectors do not fire and the plugs do not fire. It is alot easier than removing all 4 plugs + wires at the same time. Plus this way there is less chance of crap getting into your engine.

RE: How do i properly do a compression test?
 

Doesn't work correctly, at least not on a d16. I did it that way 4 times and kept getting crazy numbers. Once I pulled all the plugs/wires, I got accurate reads three tests in a row.

RE: How do i properly do a compression test?
 

jam the throttle all the way open too. you need to feed as much air as possible into the motor. and the numbers arent so important, more important is the difference between them. the closer they are togehter, the better. the overall numbers vary too much with little differences in how people test, so for us non-trained mechanics, its better to look at the range than the actual numbers. and make sure you remember where all the wires go if you take them all off at once.

RE: How do i properly do a compression test?
 

^^^
+1
That's exactly what happened to me as well. That's why I say to just pull them all at the begining. You have to pull them all anyways so just do them all at once. I however do not know if this way works differently w/ b series motors. I don't see how it could make a difference either way.

Pulling the ECU fuse is the same thing as unpluging the injectors. Either way will work fine. The object is to crank the motor over w/o having any spark or fuel in the cylinders.

Holding down the gas pedal when cranking over the car is a good idea as stated before as you want the maximum amount of air in your cylinders.

RE: How do i properly do a compression test?
 

Well said!!!

RE: How do i properly do a compression test?
 

with the b series motors you can pull one out at a time and it will work fine. im not sure if the ls motor has a different compression than my b16 but all my numbers were 180. if your within 10% on all 4 you should be alright.

RE: How do i properly do a compression test?
 

cool, thanks alot guys. appr all the info.