Dear Mr. Know-It-All,
I was in the middle of a rather large race last weekend, and midway through, my 2021 KTM 300XC started running like somebody stuffed a softball in the intake and wouldn’t idle or rev out. Upon trying to diagnose a few key areas, like spark, compression and the inline fuel filter, I ran out of quick-fix ideas and had to pull out of the race. What on earth is the problem?
Bryan Kook
via [email protected]

Mr. Kook (I love that), with today’s fuel-injected machines comes the technology necessary to let the ECU send its signals to open the gates for proper air/fuel ratios and flow. This means that there are a number of devices that collect data to send it to the ECU. I have heard of some issues with the ambient air-pressure sensor and sometimes the crankcase pressure sensor. The two sensors are interchangeable, and if your machine suddenly starts running ragged and won’t idle, try (and this helps if you have a buddy with a TPI machine) plugging another sensor in place. It should fix it immediately. I have heard from one fellow TPI pilot that he unplugged his crankcase pressure sensor and used it to test the ambient air sensor with total success.

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