Work Case #19 Honda CRF250R MX
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The Honda MX bikes are fuel injected, and at the time just kick start with no battery, so how exactly did that all work then?!
![Surprised :o](./images/smilies/icon_e_surprised.gif)
Interestingly it started effortlessly once warm, and initial checks when cold showed a good solid spark and plenty of compression. So what was causing this issue then, the cold-start button? No as it happens, and not everyone is aware that on fuel-injected bikes this “choke” control does not make the mixture richer for cold starts but just raises the idle speed slightly. Bikes, and most modern cars fitted with electronic throttles, automatically adjust the idle speed for cold starts so don’t need a manual control.
So the bike’s ECU monitors the engine coolant temperature, and the outside air temperature, and adjusts the mixture accordingly. Except this one presumably wasn’t richening things up when cold and causing the reluctance to start. OK, so how to check this? I had a Honda engine management computer thing but it needed the bike’s electrical system powered up, and the bike had no battery! Aha, of course, you have to stick a separate 12V power supply onto the bike’s loom and hey presto I could read some data.
![Smile :)](./images/smilies/icon_e_smile.gif)
The outside temperature was showing 15 degrees on a cold morning, which was bang on, but the engine temperature was over 20 deg, too high. So it must be a faulty sensor then and tried swapping that. Ah, exactly the same - oh! Borrowed another ECU from one of the second-hand bikes in the showroom, and..... all ok.
A quick swap back and forward to double check on the good bike and yes, definitely the ECU. Called Honda who tell me it can’t be reprogrammed, and the only option is to replace it.
The customer is quoted £400 ish for a new ECU but decides that is too much and takes it away as it is!
Oh, ok then...
![Confused :?](./images/smilies/icon_e_confused.gif)