Where and How do you do a compression test??? Always wondered that..

 

A compression test is done by doing the following.

1) Buy a compression gauge. A good one costs about $40 at your local parts store. Buy the kind that screws into the spark plug hole, not the kind that you just hold there.

2) Remove fuel pump fuse and disconnect Aux Fuel Pump (if applicable)

3) Start car....let it run until it dies from fuel starvation. Crank it over a couple of more times to make sure there is no fuel left in the lines.

3) Remove all spark plugs

4) Stick gauge into each cylinder through the Spark Plug ports. Screw it into place. Turn car over 7-8 cranks. (The FSM recommends 7)

5) look at the gauge.

6) Move on to the next cylinder.

 

IIRC you're supposed to hold the throttle open when cranking.

 

Ah - forgot to mention that step.

IanS

 

That helps fill the cylinder to fill completely before the compression stroke, so you will get slightly higher compression than otherwise. But as long as you are within the recommended pressure range, it's more important that you don't have a wide variation in cylinder pressure from highest pressure to lowest.

It's also recommended that you do the test with the engine warm. I think maybe the rings seal better when the engine is warm and the cylinders walls are coated with oil.

 

So what numbers are good? Bad? Nuetral? etc.,.?

 

according to the FSM - 185 is spec.

Minimum is 125 or so.

For example, mine are 175 - expected for the current milage on my engine.

IanS