Checking Compression Question

[duke16]

When doing a compression check on each cylinder, should I leave the other spark plugs in, or remove them all? I've seen threads mentioning both ways.

Also, just checking I've got my procedure down. I just attach the gauge to a spark plug hole and crank the engine for a few seconds to build pressure. Is that right?

 

[DirtyDog]

I've been told that the engine should be warm and the throttle should be fully open. Also, don't forget to remove the fuel pump relay.

 

[Cobraguy]

And disconnect the coils.

By taking the plugs out, you are making it easier on the starter, battery, etc to crank. That's it. If I was just checking one or two cylinders, that's the only plugs I would pull. If I'm checking them all, I would pull them all. They all have to come out anyway.

 

[duke16]

Do I have to disengage the fuel pump if I pulling the wires and coil pack?

 

[Cobraguy]

Yes. Just pull the pump relay in the box under the hood. Your owner's manual will tell you what one.

 

[duke16]

Thanks.

I did the passenger side today and all four were within the 120 - 130 range. Does that seem low? I help the ignition down for about 4 seconds each time... so maybe it wasn't long enough...I'm not really sure how to tell when 1 stroke has completed.

 

[cleudard01]

I usually try around 10 revolutions on each cylinder to get max reading & I do a wet test too to check if rings are bad.

 

[Cobraguy]

Watch the gauge. It will take about 3 good sized jumps then pretty well level out. That's on a good cylinder.

 

[BrooklynBay]

http://www.explorerforum.com/forums/showthread.php?t=204909

 

[duke16]

For future reference for anyone else checking all 8 cylinders... have someone on standby to jump you. I only seem to be able to get through 6 before my battery dies.

 

[Cobraguy]

Then you need to check your battery and charging system. And that will also contribute to poor compression readings.