Hayabusa Rev Limit error
JimSpencer - 17/9/12 at 01:07 PM
Hi All
Appealing to the collective knowledge to get a friend out of the mire..
He's got a Hayabusa in the back of a Davrian - and a very interesting tool it is too.
But it won't rev past 8k.
Now this isn' the "coughing and spluttering" sort of won't rev it's the:-
"runs beatifully until it hits what feels just like a smooth cut" at 8k
does this in every gear.
So my thoughts are it's got to be a design feature buried in the ECU that's not seeing something it should so is rev limiting itself, have
heard about a rev limiter while it's in neutral? but can't seem to find any more detail on that..
So am wondering if that might mean there's a gear indicator fault somewhere etc etc.
But that could be totally wide of the mark,. not got much of a clue really!
He has tried another ECU, exactly the same issue.
So I think it must be the ECU is missing an input from something, or is getting an input it shouldn't of course..
Anybody got any ideas, or preferably had this and fixed it 
Thanks all
MikeRJ - 17/9/12 at 01:32 PM
Is the engine standard, or does it have aftermarket cams etc?
Jon Ison - 17/9/12 at 01:32 PM
is the rev counter reading correctly ?
JimSpencer - 17/9/12 at 01:34 PM
Hi
Yes, totally stock, except the wiring and dash.
Yes re-counter reading fine.
BobM - 17/9/12 at 02:20 PM
The ECU will run different maps for neutral/different gears but none of those maps will cut it at 8k. Nor will any of the interlocks (sidestand, kill
switch, tipover switch etc.) - they either stop it turning over to start with or cut the fuel injection completely.
How confident is your friend that he has his dash calibrated correctly and that the 8k is really 8k?
twybrow - 17/9/12 at 02:42 PM
Could it be in a limp home mode? Ie a wiring fault, or other engine related fault is causing the ECU (new or old) to go straight into a limp home
mode, and hence limit the available revs? Have you checked for any fault codes?
MikeCapon - 17/9/12 at 02:45 PM
If the clutch switch is permanently shorted the secondary injectors won't work and it will run like the proverbial sack. You can watch the
injectors with the airbox off and it is obvious if they are working or not.
JimSpencer - 17/9/12 at 02:53 PM
Hi Bob
Yup the rev counter match's the engine speed 8k is 8k etc
Hi Mike
It runs and pulls fine, seem to have plenty of torque just gets to 8k, and stops going any higher.
Hi Twybrow
Ahh - would it have full performance in Limp home mode? i.e go like a train at the bottom end? if so perhaps we're onto something?
twybrow - 17/9/12 at 02:57 PM
It could well do - when my last engine went into limp home mode, it too topped out at 8k revs. The difference was, the cause of my limp home mode was
also meaning rough running - your sounds like it appears to run fine. Is there anything that the ECU is looking for a signal from, that it cant find
as it has been removed? Eg - cold start/idle valve, secondary injectors, road speed sensor etc...?
Do you have access to a fault code reader? If not, can you get the car to someone who does, or borrow one?
Jon Ison - 17/9/12 at 03:00 PM
I think my next post of call would be pick the phone up, mal. Yorkshire engines, Damien day tuner.....
MikeCapon - 17/9/12 at 03:18 PM
The secondary injectors are primarily for high rpm operation.
There is no 'limp home' function on the Hayabusa apart from some safe maps that will allow way over 8K rpm
The fault codes are dispalyed on the standard Hayabusa dash.
Permanently shorting the clutch switch will disable the secondary injectors without any fault code showing. You need either a relay or a second switch
to start the motor to avoid this happening.
twybrow - 17/9/12 at 03:29 PM
Cam timing? - seems that Busa can suffer chain
stretch, and a little bit of stretch is enough to thorw the cam position sensor off...
BobM - 17/9/12 at 03:36 PM
quote:
Originally posted by twybrow
Cam timing? - seems that Busa can suffer chain
stretch, and a little bit of stretch is enough to thorw the cam position sensor off...
Not a problem I've heard of before and IIRC the
cam position sensor doesn't do a lot once the engine's running.
Which year Busa is it?
MikeFellows - 17/9/12 at 04:11 PM
is it a pre or post 08
as the pre 08 didnt have secondary injectors 
nick205 - 17/9/12 at 04:26 PM
Does it stop flat on 8k like it's on a limiter? Just wondering about the basics like fuel/air restriction somewhere - I'm sure it's
been checked mind, but it can sometimes be the things you rule out early on.
JimSpencer - 17/9/12 at 07:27 PM
quote:
Originally posted by twybrow
Cam timing? - seems that Busa can suffer chain
stretch, and a little bit of stretch is enough to thorw the cam position sensor off...
Hi
Followed that link and done some more digging - I think we have a likely candidate, symptoms sound exactly like this, works perfectly and seems to hit
a none existant rev limit.
Will report back once we've given that one a go!
Thanks all for your help