I am testing my pressure sensor on an 89 (S5) Turbo II JDM. It is an N370 sensor on a JDM motor. Anyway, at atmospheric pressure (no vacuum applied) and we are at about 600 feet above see level in St. Louis, the volt reading is 2.03 V. At the recommended test level of 3.9 inhg, it is reading 1.70 volts. The FSM recommends 1.9-2.1. Is this too far out of range? Should I replace the pressure sensor?

 

First, what exactly is your setup? And what symptoms are you trying to trubleshoot by checking this sensor? Are you throwing a code? It doesn't seem too far off... and I don't think it matters all that much anyway as long as it's not totally fubar'd. Here's why:

The pressure sensor does affect timing under boost a little bit, but it is mostly determined by the engine load measured by AFM. That's why if you put a Fuel Cut Defender on your car (not talking Rtek here, they don't make s5 turbo Rtek's yet), and the pressure sensor doesn't "see" all the boost, the car can run alright without detonating provided you have a decent setup. If the car is stock or isn't boosting enough to hit even fuel cut, then you're probably not going to detonate anyway as long as you have good gas in it.

 

It is reading a little low, but unless you're willing to go look for another unit (kinda rare) or buy a new one from the Mazda dealer (expensive!), just use the one you got...
It's really only important for the overboost fuel-cut.


-Ted