Hi all,

I’ve just bought an f4i Rossi rep UK model and love it. But I do have an issue with the tacho not working. I did a quick search on here and found some advice on fault finding the issue, I’ve come to the conclusion that it’s an ECU issue, voltage low on yellow and Green wire. Now my problem is that I can’t seem to find a direct replacement ECU I have a 38770-MBW-D41. I have found a 38770-MBW-D21 with ignition switch, HISS reader, lock set and 2 keys. Will this work on my bike with no issues and no reduction in power.
tia for you responses

 

Does tach do full-sweep of RPM-range when you 1st power ON? If not, tach is bad, not ECU.

Can't measure voltage on tach line because it's not analogue voltage signal. It's digital square-wave for each ignition-pulse. Looks like this on oscilloscope.



1. measure tach-signal at ECU connector with oscilloscope.

2. measure tach-signal at clocks connector with oscilloscope. Same shape as in #1???



Other ECU # should be OK. They were both used on 600F4i models from 2001-2004 with D41 used up to 07. Primarily for OZ markets. The "D" part shows they're same model/part with "21" vs. "41" being minor changes. Don't waste your money & time swapping ECUs until you've actually identified it as problem. Test tach signal 1st. Could be tach is bad or wiring in between is bad.

 

Dannoxyz thanks for the info, much appreciated. Tach does needle sweep when switched on just sits at 0 rpm when bike running. I’ll try and get hold of an oscilloscope and test as you suggest.
thanks again

 

Another thing that might be worth mentioning. The guy I bought the bike from had a haltech gear indicator fitted and said the tacho stopped working 2 weeks after this was insalled. Could this have something to do with the tacho not working?

 

yeah, he probably snipped wire going to tach to install gear indicator. Remove it and restore harness back to 100% factory OEM condition.

 

Hi dannoxyz. Managed to get hold of an oscilloscope, with the clocks unplugged the reading looked how you suggested it should at the clock end (see below)


however with the clocks plugged in I got a very different reading


I’m guessing this would indicate a short within the clock unit causing some electrical interference and this means the clocks are bad?

sorry for the dumb questions, I’m no expert as you can probably tell.

cheers

 

Great job! So ECU is perfectly OK and signal makes it to clock connector properly. Wiring is OK.

Lowered signal when plugged in can be caused by different things and usually OK. But in this case, it's most likely caused by splitting signal and supplying 2 separate circuits: tach and gear-indicator. This lowers high-impedance tap and drains signal too low.

Disconnect gear-indicator and restore harness back to 100% factory OEM condition. Then tach will work just fine like it did when leaving showroom floor in 100% factory OEM condition. Proper gear-indicator to use is digital unit that connects to diagnostic connector and gets gear-position data from ECU.

 

Thanks mate, you’re a star. I’ll get the gear indicator ripped out and 🤞 all will be good!
thanks again, appreciate the help

 

So now im really confused. I’ve removed the gear indicator, it was a haltech plug and play with the signal wire spliced into number one ignition coil. Tacho still not working! Is it safe to say it’s the clocks at fault yet?

 

Hmmm, very odd. So gear indicator didn't connect to tach line?
Certainly sounds like tach is bad then. Strange...