Did a compression check on my car with a standard autozone checker. S4 Turbo with 169,000 on the OD. Both Trailing plugs were removed. And tested from the trailing.

Front rotor:

95 psi hot Throttle wide open
85psi hot Throttle closed

Rear rotor:

85 psi hot Throttle wide open
75 psi hot Throttle closed

As I understand it, mazda specs indicate that a variance between rotors of no more than 15psi is ok. What worries me is the 75psi closed

Any opinions?

 

Well, our test S4 NA has something like 50-60psi on both rotors and drives fine, just starting is not really easy

 

I have an S5 TII with 60-60-85 and 85-85-85. Runs great except the blown coolant seal. Tough to start on hot starts only.

 

how did you get psi readings for each face? i thought psi gauges required several turnovers for a single reading.

 

Take the check valve out of the gauge, plug it in and crank the engine. The needle will bounce. Each bounce is the compression of each face of the rotor.

 

bad battery/starter can also cause low compression numbers , correct?

 

Yes,

Per FSM, your compression readings are DIRECTLY related to cranking speed.

Unless you have the proper equipment, the home compression test is merely a guide, its not the factual numbers.

Jarrett

 

Looks fine to me, and just about average for the amount of miles on that motor.

I've edited out the closed throttle numbers, cause they don't mean anything.

If this is a stock motor running stock boost, it still have several years left on it.  If you're running more boost and significantly more power, I would highly recommend getting a rebuild within the next year or two, if you're thinking of keeping the vehicle.



-Ted

-Ted