I was told that if I change the airbox on my RZR-S to the UMP airbox, that I need to put an EFI controller as it will run too lean without. I was under the impression that fuel injection was suppose to take care of this automatically.

Any ideas/suggestions/comments...Thanks in advance!!

EFI wont auto correct for mods like that

The EFI only adjusts for altitude and temperature changes.

Will it really lean out that much over a UMP install?

It allows it to breath better ... so more air......I say run it without for a while and report back

CApt

Call me crazy, but isn't that was an air flow sensor is for? The same one that decides air density and flow into the intake as you change altitudes and temperature?

Not saying a tune isn't helpful, just saying it sounds like you don't believe in the hardware already there. What's the difference between more air flowing in due to temp/altitude or more air due to a new intake.

The exhaust part, now that I understand, no sensor on that end IIRC

Yes it will run lean. They run on the lean side anyway and introducing more air without more fuel has bad results.

im calling bs on that.have had the utv inc air box on both rzrs for about 1000 miles.no issues.the utv inc airbox is basically the same except for a better seal design.put it on an run it , you will be fine

show me evidence on this particular vehicle

I know they run lean already, all of new stuff does. But going boom due to a new airbox is a stretch on a vehicle with a sensor designed to adjust for airflow.

I am fully aware of what happens when you go too lean but I too am calling BS over just a UMP.

You don't need a efi programmer. An UMP isn't like a high flow cold air intake.

Thousands of RZR owners are running the UMP with their stock gear.....no issues. I've sold well over 100 of these units and there's a VERY small percentage of those sales where people purchased fuel controllers. I've got one on my RZR-S and it runs like a raped ape....well, a 36 RWHP raped ape........