Dear Sarge,

I recently bought a used RZR 900. It was not running but I thought it would be an easy fix. That has not been the case. When trying to start her, all I get is a back fire through intake and it dies. The problem I am having seems to be no pulse to the left injector. Following the Service Manual, I have determined there is power to the left injector and on the signal return wire to the ECU. I swapped the ECU for another unit but I get the same results. Right now Sarge I am stumped. Can you help me with diagnosing fuel injection problems?

Dorian Ames

La Sal, Utah

I see Boot that you are following the factory Service Manual. That is a good thing, up to a point. What the factory Service Manual will not do is determine what a previous owner has done to your Zooter. It could be something as simple as the previous owner swapped the injectors, left for right. That will cause backfires. The crankshaft woodruff key could be partially or fully sheared, causing the timing to be off. Or the ECU is getting an over temp signal and if it goes into limp mode, the ECU will not allow both cylinders to fire until a certain cool down threshold temperature has been reached. Check that out in your Service Manual. Beyond that, long distance troubleshooting of electronics ain’t easy Boot! Sounds like you purchased a “Pig in a Poke”! Laugh Boot! Maybe a trip to the Local Motor Pool would be your final step with a list of all your tests and results. Pushing your Zooter there will build character and give you time to reflect on this purchase! Dismissed!


Fuel injection system problems can be difficult to sort out, but don’t overlook simple solutions. Be sure the fuel pump is working in the engine on key position. Check for fuel pressure at the fuel rail. Replace the fuel filter according to the service schedule for your machine, or more often if you ride in extremely dusty or muddy conditions.

See UTV Action’s full test on the RZR 900 Trail here: POLARIS RZR 900 EPS – UTV Action Magazine

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