Testing the RPM Sensors

Today, I downloaded and set up a program that John Lussmyer wrote called ZillaConfig. It's essentially a desktop application that connects to the Zilla controller and provides you with a desktop window for configuration. It's really pretty slick. If you interested, you can get it here.

But perhaps the neatest thing it does is allow you real time graph of the Zilla's output while the car is running. You can watch motor current, throttle position and lots of other things, including RPM. So, with the ZillaConfig program loaded up and running on my laptop, I set off for testing.

Loyal readers (both of you) will remember that I installed both sensors on the car a few weeks ago; however, I could only wire one up to the Zilla at a time. So first up was the older style sensor that sits on the end of the tail shaft.

I decided the best way to test would be to put the car in first gear and spin the wheels up to 10 MPH, then 15, 20 and 25, taking RPM readings at each point. Simple enough. I ran the test on the old sensor, and then swapped the leads to the Zilla and re-ran the test with the newer sensor. Here are the results:

Old Sensor
10 MPH = 1600 RPM
15 MPH = 2500 RPM
20 MPH = 3400 RPM
25 MPH = 4300 RPM

Huh, I just noticed that there's a 900 RPM difference between each entry. Anyway, here are the results of the second, or newer style sensor:

New Sensor
10 MPH = 2500 RPM
15 MPH = 3700 RPM
20 MPH = 5000 RPM
25 MPH = -

The Zilla wouldn't let me over 5000 RPM, so I couldn't get to 25 MPH. Clearly, the two sensors are not sending the same signal to the controller. Bad news for me. I need to use an RPM sensor to protect the motor from over spinning it, so doing without really isn't an option. But if the only one I can use is the older one, that means the end of the tail shaft is occupied by the sensor. That in turn means that there is no room for the pulley that I need to use to drive the A/C system. In short, old RPM sensor equals a very hot summer in the Z3.

There are a couple rays of hope on the horizon. First, the supplier that I got the sensor from is working with the manufacturer to find out what can be done, if anything, to make it work. Second, I could have a piece machined that would screw into the tail shaft and extend it by an inch or so. While not optimal, that would work.

Before I run off and have that piece made, I need to go to an A/C shop and have them look at the car and determine if it's even feasible to run the lines needed in the very cramped spot the compressor sits in. Of course I can't do that until the car is out of the garage. That tachometer can't come soon enough!