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Discussion Starter #1
Hi all I have recently rebuilt a MV F3 675 non abs engine.
bike has been on the dyno today but the bike seems to be in limp mode as it will only rev to 13800-14200rpm, the rev limiter is set to 15000 in the ecu.
The bike isn't showing any fault codes.

Any help much appreciated ?
 

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Not sure that's a limp mode. Most limp modes would severely limit the RPM and or power not just 800 rpm or so.

A few questions.
1. What engine mode and settings are you using?
2. Was the power at 13000 rpm what you would expect or low?
3. Are you still running the exhaust valve?
4. How did you change the RPM, or did you send it away for a change?
5. Can you run a datalog (external or ECU)?

Cheers
 

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Discussion Starter #3 (Edited)
Not sure that's a limp mode. Most limp modes would severely limit the RPM and or power not just 800 rpm or so.

A few questions.
1. What engine mode and settings are you using?
2. Was the power at 13000 rpm what you would expect or low?
3. Are you still running the exhaust valve?
4. How did you change the RPM, or did you send it away for a change?
5. Can you run a datalog (external or ECU)?

Cheers
1: sport
2:around 115bhp around 5hp lower than I would expect
3: no (long gone)
4: ecu flash by dyno tuner
5: unfortunately no

The only reason I'm thinking "limp mode" is because I know if you have an abs bike with an abs fault it runs a similar rev limit
 

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If there's an abs fault you will get an error code, while the bike is running, not necessarily once you have turned the ignition off as the abs is a code that only displays if it's in active error and does not need to be stored.

When dynoing the ABS bikes you will get an ABS fault as the front wheel is not turning so I'm surprised that you say it limits the RPM on the F3. How would you tune it on the Dyno if it limits the rpm?

On the F4 an ABS error does not limit the RPM either on track or on the Dyno, same ECU and hardware but a different flash.

I'm assuming as it's a non abs engine you are running a non ABS ECU flash and the wiring etc is non ABS.

If you can't log the ECU, I'd ask the tuner to flash the rpm limit to 12000, check the flash and rev limit in each gear, then increment the flash and repeat.

Is the current rpm limit stable and the same in all gears or different in the higher gears?
 

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Discussion Starter #7
It could also be an inaccurate tach.
Dash may be inaccurate but the bike has been on same dyno a number of times and has always behaved as I expected,

Another observation I've made over time is that the bike runs different maps when the clutch switch is bridged or not.

I'm hoping someone can give me a list of what sensors / swithches causes the bike to run a lower power / rpm limited map
 

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My advice don't mess with the clutch switch. If the ECU thinks the clutch is in, then the rev limiter for neutral will be used which is lower than for any gear. Typically we see issues when people fit aftermarket shorty levers that don't operate the switch correctly.

Most of the sensors will affect the ECU's decision on power, its a long list.

I suggest you list the modifications you have made from levers, loom, blipper, and the flash used. Then we might be able to suggest what is the most probable cause. Most decent ecu software for flashing, can see the sensor and error data in the ecu (request over the CAN bus), I'd be surprised if your flasher (forgive the term) cant see the data live, even if he cant record it.
 
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Discussion Starter #9
Items disconnected ?
-Side stand switch
-Exhaust servo motor
-Lamda sensor
-Clutch switch
-Front and rear brake switch
-Fan
-All lights

Auxiliary starter button fitted
Keyless ignition switch
Race ecu fitted
Replacement dash fitted (same part number)

I got the bike booked in at motocorsa on Friday to get it plugged into computer, otherwise I think I will take while to track the issue down, fingers crossed
 

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First thing is to check the clutch wiring. Have you bridged it or left it open circuit?
 

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Discussion Starter #12
Been to the dealership, I'm no further forward with solving the issue.
Got a different loom coming this week, hoping that might solve it, but I'm not holding my breath
 

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Discussion Starter #13
New loom fitted, also measuring sensors as I change the loom, found that the engine pick up was slightly over spec resistance 711ohm (spec is 600-700ohm), measured it a few times off the bike and it's always different 712,699,678.

So I'm presuming this may be the issue, but can't test it before my next track outing so fingers crossed that's it fixed?
 

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The measurement may vary depending in the quality of your multimeter, either way its at the top end of spec.

Fingers crossed for you, however I doubt a few ohms will make that much of a difference. If it was fine when first started, and then got worse, you might attribute that to thermal issues affecting the sensor, but as you have not mentioned any time effect I assume its a constant performance issue.

In one post you say its a Race ECU, if you bought the MV ecu rather than flashing your own, I'd swap over the ECU just to check that too.
 

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Discussion Starter #15 (Edited)
The measurement may vary depending in the quality of your multimeter, either way its at the top end of spec.

Fingers crossed for you, however I doubt a few ohms will make that much of a difference. If it was fine when first started, and then got worse, you might attribute that to thermal issues affecting the sensor, but as you have not mentioned any time effect I assume its a constant performance issue.

In one post you say its a Race ECU, if you bought the MV ecu rather than flashing your own, I'd swap over the ECU just to check that too.
I'm electrician by trade so top quality calibrated tester.

11ohms over spec out of a range of 100 ohms shouldn't cause the problem, I just changed it as a matter of course as it is out of spec.

I did suspect the flashed ecu and tried the original for comparison, Image attached is 5 dyno runs on different ecu's, 2 of which are brand new
 

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Discussion Starter #16
limiter problem solved, then the engine shat itself?, started making less and less power then dropped another valve at few thousand revs.

Time for a new bike I think?

Hands up for some tasty upgraded parts
 

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What was the actual fault before demise?

Sorry to hear you lost another valve.
 

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limiter problem solved, then the engine shat itself?, started making less and less power then dropped another valve at few thousand revs.

Time for a new bike I think?

Hands up for some tasty upgraded parts
Wow sorry to hear of another dropped valve :(

I may have lost count, but is it the 3rd time?

I remember you sent out the head to get redone with new guides etc. Is it the same one?

Im interested in what you have to offer, PM the list once you get it together.
 
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