2011 YZ450F Ignition Problem

Hello friends!

I'm desperate for help. About a month ago, while riding in the woods, my 2011 YZ450F started to fail until the engine stopped. I restarted the engine, it ran for about a minute and died again. After this it didn't started anymore. My Power Tuner indicated error 33 (ignition coil not receiving signal). Ok, I took the bike back to my mechanic, we tested all the electrical system (following all the steps shown in the Owner`s Manual) and everything was OK, including the ECU. In fact we also tested my ECU in another YZ450F and it ran ok. Also, the fault code disappeared from the Power Tuner. After assembling again the bike started and ran properly. I took the bike to a Yamaha dealer, who tested everything and had the same diagnostic: the bike has nothing.

After that, I rode for about 2 hours without any problem. One week later, after only refueling and washing (I have the bike for one year and it was always refueled with the same gas, same station, and washed just like the same) and the symptoms appeared again. It ran for about 2 minutes, without idling, stalled and did't fire again. No error in Power Tuner this time.

Please, I really need to help, because nobody can find the problem with my bike. I was seriously thinking in selling it after this, but I want to give it a last try.

Thank you very much for your attention!

You haven't done anything to isolate an intermittent problem. Your ECU worked fine in your bike for a while, so testing it in another bike for a short period is not much help. If you spend some time looking very closely at all the connectors and wiring and they are good, you could buy a new ECU and see if that fixes it. If it eventually does the same thing, sell on of them on TT or eBay. Absent sophisticated instrumentation and test harnesses, you kind of have to Easter egg it. Make a fault tree and work the most likely causes first. Carbs are pretty easy.

Update: today I kickstarted about 50 times and the engine started, but did not idle. After that it didn't start again. I resetted the ECU map and then it started with just two kicks, idle ok. With cold engine it did not fire easily again. Any ideas?

Thanks again!

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