HOME COMPRESSION TEST

Think you messed something up? Think you may have lost compression in one of your cylinders? Well, there is one easy way to tell without having to drive to your mechanic to get a compression test. Do as follows:

1- Turn on ignition and start motor.

2- Let the car idle until warm, and have a steady idle.

3- Starting with cylinder 4 on the left side of the motor, pull out each spark plug wire one by one, and listen for idle drop. Replace spark plug wire before testing next.

What should happen is the following:

1- If your motor is alright, when you pull out the spark plug wire in each cylinder, the idle should drop significantly.

2- If the motor is damaged, and one or two cylinders in particular are the culprit, when you pull out that spark plug wire from that cylinder, the idle will NOT change, but it will remain constant, and that means that you are NOT getting compression in that cyldiner, and that is the root of the problem.

If you try this, and the idle drops each time, then your bottom end may not be the root of your problem. If it does drop in any particular cylinder, then that cylinder could be cracked, scratched hard, or that piston ring could be burnt beyond belief.

 

or just get a compression guage and actually test it.

 

Of course it will drop when you pop out a plug wire because you are simulating a misfire. If you don't notice the engine do this, then that means that you were already getting a misfire which would throw a code thus rendering your test useless because you would already know.

 

Sorry about that. I had a long bad day. You're just trying to help

 

well, it would tell you that a cylinder isn't firing gas. but it doesn't tell anything about compression really. a bad injector, injector clip, plug wire, cap with a bad contact, etc, etc would all cause a misfire in a given cylinder to begin with.

 

If you arent firing on one cylinder (which is what this test will tell you) you wont have a steady idle to start with nor will acceleration be smooth.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ActiveAero &raquo;</TD></TR><TR><TD CLASS="quote">or just get a compression guage and actually test it.</TD></TR></TABLE>

 

http://www.sears.com/sr/produc...89000

 

that test has been around for ages. All it tells you is which cylinder is the culprit of WHATEVER problem there may be. Basically, if the performance of the engine doesn't significantly decrease, then you know what cylinder is bad. This could mean : the plug is bad, the wire is bad, the injector is bad, the compression is low, the sleeve is cracked, the valves aren't sealing, etc etc