I have been wondering for sometime now but never got an answer.

I have been told that you have to take the compression from the bottom plug. Which I do. But whats the difference in the reading if its taken from the top plug?

 

Per FSM, compression tester goes on top (trailing) holes. No idea why.

 

Really?!

I asked the guy at mazda and he told me bottom....And I said'' are you 100% sure?!'' And he said ''yea...''

Anyhow, whats the difference between top and bottom?

 

Never mind, close this thread. I did the test and there is absolutly no difference between trailing and leading in the readings.

/thread.

 

But we were having such a wonderful discussion...

I can't see how it would matter where you screw the gauge...maybe Mazda says top just because it's more accessible. Been lots of threads on today about compression testing...and most have touched upon this. Good to know you got the same results.

 

Fixed.

I dont know what the difference would be when using the mazda tester.

 

Thats good to know, I never tested that, I always thought that maybe the leading was best and the the smaller hole in the trailing would restrict the pressue into the gauge a little causing lower readings or something.