Polaris RXL and Indy 500 EFI Select Monitor Software and Interface


I love my old Polaris 92 RXLs. When the EFI is right and the engine is sound they have a great crisp throttle response and they are fairly fast as the old triples went. Properly tuned, they always start on the second pull, even stone cold.

For a long time I had to guess at sensor readings and the throttle position sensor settings by testing them with an ohm meter because the Select Monitor from Polaris was hundreds of dollars.

Well that is no more. For $20-25 you can have the functionality of the Select Monitor by using a free program, a special USB cable, and a Windows computer or laptop.

The first order of business is to order the interface cable. You need to be accurate here. The interface cable is a USB on one end and a series of wires on the other.  My cable is made with the FTDI chip, the cable that I tried with the Prolific chip did not work at all and was a waste of money.

interfacecableThe cable needs to be an RS232 TTL with 5v signaling. There are other cables that are RS232, but not TTL signaling or voltages other than 5v. You need to make sure that it is TTL 5volts.

My cable is clear on the USB end. You can get black ones, but I prefer the clear since you can see the green and red LEDs for transmit and receive and tell if it is communicating.

Digikey.com is an electronics supplier in Minnesota and they have them here at $21.07 plus s&h. When I ordered stuff for the RXL from them it came USPS Priority and shipped in a business day.

So now you have your FTDI RS232TTL 5v USB cable. You will want to go to this web site and download the FTDI drivers for your computer. They have VCP or DLL based D2XX drivers. I am using the D2xx drivers, but either should work.

Next you will want to go to this page and download the Select Monitor program Link #2. Install the program, and I went for both the desktop and quick launch icons. You can launch the program without it hooked up to check it out.

Unzip the FTDI drivers into a folder on your desktop. Plug the cable in and your computer will find new hardware. Guide it to the FTDI drivers in the folder you just made. You will have to do this twice, once for installing the USB device, once for the serial port. Once it installs both unplug your cable.

On the EFI computer where the main harness goes in there is a smaller  six wire harness with plug on the harness. There is a dummy plug in it to keep the connections clean. Pull that out.

plugdiagramorigHere is a rough approximation of the plug and a diagram that tells you which wires to put where.

The cable will come with more than the three wires that you need. The others are not used.

The ones that you are concerned with are the Ground (GND), the Transmit (TXD), and the Receive (RXD).

The smart cable and chip are powered by the USB so you only need the three. You will want to consult the data sheet for your cable to determine which wires are RTX, TDX, and GND. The cable linked above are as color coded in the diagram above.

On my cable I stripped the outer casing back to make it easier to work with. This is a good idea since there are two black wires, one for the shielding, one for the ground. You want the ground that is in the wire bundle.

I have not found the right terminals yet to fit the plug connectors. At that point I had to get a little creative. I stripped the wires back a half inch and tinned them with a soldering iron to make them more stiff.  I inserted the wires into the connector and had them make contact by also inserting a piece of solid wire to hold them against the connection tabs. It worked pretty well and was a sound connection.

Now you are ready to plug in the USB cable. My laptop recognized it and installed the software that we installed above.

Now go to the control panel on your laptop. Choose System, then Hardware, then Device Manager. At the bottom of the device manager there is a USB controllers entry. Click the + next to it to expand the menu. At the bottom there should be a USB Serial Device. That shows that your smart cable is recognized and installed properly.

Next in the device manager open up the Ports (COM & LPT). Again you should see a USB Serial Device followed by a com port. It will say something like USB Serial Device (COM5). You need to know this for two reasons. One, you need to have both the USB and com port installed for it to work. Two, you need to know what port your cable is on in the Select Monitor Program.

Now you are ready to open the program. Click the icon and it will open. Pick your com port, and click Connect. You should see a lot of activity on the red and green LEDs on the smart cable. Check off the values that you want to read and they should fill in fairly quickly.


Here is what mine looked like after I set the TPS.

Setting up the cable and software was a worthwhile effort on my sled  because the throttle position sensor was a little off, the idle trim is a little rich, and my air intake sensor is telling the computer that it is 73.4F when it was really 41F as indicated by the crankcase sensor. That would make it run lean, a bad thing for sure.

You can set your throttle position sensor up by loosening the screws on the side and rotating it. The proper procedure is to remove the throttle cable and back off the idle screw until the butterflies are all of the way closed. Rotate the TPS until the 0-39 number just breaks to a positive number. As shown above, at idle it was between 3-4º per the Polaris Manual. It had conflicting information on what the wide open reading should be, it says that it should be over 74 in one spot and over 77º in another. On mine it was well past either value.

Unless it has been running, the crankcase sensor and air intake temperature sensors should be at shop temperature.

The voltage reading is handy to check the charging system and operating voltage. It should be over 12v sitting or idling and over 14 volts running above 3,000RPM.

You can also check the throttle position sensor for wear in the TPS Graph section of the software. What you are looking for here is flat spots or gaps as you gradually open the throttle.  That indicates a flat spot in the TPS resistor, and that it needs replacement.

Most people aren’t running remapped chips in the RXL, but some do. If you want to share that map, the software gives you an option to do that.

I really like my RXLs, and am very happy that I can check and calibrate the EFI on them without spending hundreds of dollars on a Select Monitor.

Thanks goes out to Rensu who wrote the Select Monitor program and was generous enough to share his efforts for free to other riders.

Hat tips also go out to Mr Holmquist, Baldur, and Ugly Old Poo Kid over at the Snowmobile Fanatics forum for putting me onto this and some guidance along the way.

This is just a first pass at this article. I encourage comments, corrections and additions.