YBR 125 - Cutting out

[YamMan22]

Hi there, new to the forum and looking for some guidance please.

I've recently rebuilt my project Yamaha YBR125 (2009) EFI model.

Yesterday I took it on its maiden voyage and it started cutting out, but it would instantly start back up. It appears to be mainly cutting/bogging out when you achieve higher RPMs, but randomly also I only rode it for about 15 mins.

After checking and testing various connections, I found a fault with the: Throttle Position sensor Output voltage, although the Input voltage is fine at 5.00v.

The yellow/blue wire on the throttle position sensor is showing 0V when opening the throttle, Haynes suggest the voltage should raise when opening the throttle.

This yellow/blue wire goes to the ECU and have checked continuity and it is good.

So I guess now either the Throttle Sensor has died or could the ECU be the issue?
Thanks for any help

[WD Forte]

What fault codes are being displayed?
Getting a 1-5 or 1-6 flash up on the eml indicates a tps fault
As the tps is basically a variable resistor, I'd put a meter on the power in and tps signal out pins and
watch the display as I steadily worked the throttle open and shut.
I would expect to see a smooth change of resistance as I did it
Anything else would suggest a worn wiper or track.

If it is faulty the snag is you can't just buy a resistor and bung it on as its a compound assembly
with other sensors in it and I'm not aware them being available seperate from the throttle body
Second hand ones may easily be just as worn so that's a gamble.

New throttle body assemblies are hundreds of quid from foulups but you can get aftermarket ones from China for 80 odd quid
ofn that ebay place
____________________
bikers smell of wee

[YamMan22]

Thanks for the help WD Forte

Unfortunately on this YBR there is no EML on dash

Ok I have tried what you said to do and hope I did it right, assuming here that the Blue wire (V pin on connector) is Power in and the Yellow/Blue (T pin) is TPS signal out.

I'm getting 3.50 ohms (20k resistance setting on MM) between these 2 pins and the value is not changing when I open/close throttle.

Yes as you say you can't just buy the electronic sensors new, but can get one second-hand for about £30, so could be worth a gamble!

Definitely can't go for a genuine new one, too expensive!
Cheers for helping

[WD Forte]

lemme guess, no indicators either?
brown seat? bar end mirrors? no mudguards?
Show us what you did to it
____________________
bikers smell of wee

[YamMan22]

Haha, no I didn't cafe-racer it or anything else, it's pretty much factory standard but just restored from a freshly painted frame.

I am assuming it never had a EML (I don't have any unaccounted for connectors)... And this loom has separate LEFT + RIGHT turn signal warning lamps

When I got it as a project it had aftermarket cheap clocks (Km/H) type.

I changed these clocks to a better version than above (ones with MPH), but not genuine as was very expensive... I fitted Honley HD1/HD2/HD3 clocks.

Thanks

[WD Forte]

As a quick fix
You could connect a small ( 2.2) wattage bulb between the light green wire from the ECU and ground as a temp eml
Normally
At ignition on it should light up as you hear the fuel pump spin up to
pressurise the system and stay on until the engine starts then go out

But
if the ECU detects a fault it will flash a 2 part code
for instance, 1 long 5 short for error 15
1 long 6 short for error 16 and so on
15 and 16 are both tps related faults

I would do this before spending any money or parts
____________________
bikers smell of wee

[YamMan22]

Thank you very much WD Forte,
I will do what you suggest and will post back my results soon!

Thanks again for the help and knowledge

[YamMan22]

Hi there,

Only getting a chance to look at bike today...

I've tried connecting a 1.7w bulb to the light green wire, not getting any codes/lights on ignition stage (tried with and without fuel tank connected).

Not even getting any voltage from this green wire.

The bike has this green wire on the 6-pin connector block in headlight cowl, so I guess originally I did have a engine warning light.

Thanks

[WD Forte]

All YBR from 2007/8 had ECUs so EMLs

The other day I only had a brief glance at the diagram without me glarses on and mislead you a bit
Just found me glarses and had a better look

The light green isn't a supply wire but is a ground wire switched via the ECU
hence your getting no voltage.
The eml bulb gets its supply via brown
( switched live from ignition switch)
and lights when the ECU switches it to ground

In Brief:
Brown to one side of blub, light green to the other side
HTH
____________________
bikers smell of wee

[YamMan22]

Hi WD Forte,
Thanks for the help mate, that would make sense!

Nice one, I will try it this afternoon cheers

[WD Forte]

Strictly speaking.
The light green isn't a ground cable per se but actually a signal wire
which gets pulled low when lighting/flashing the eml or communicating with an OBD device.
____________________
bikers smell of wee

[YamMan22]

Hi WD Forte,

Ok I did what you said (connected 1 side of bulb to permanent live and the other to the light green wire).

and the bulb is just lighting up for a few seconds (on ignition) and then going off.

I then tried unplugging FI - Nothing
Unplug ignition coil, again nothing

Then I tried unplugging Engine temp sensor... This did work, had 2 slow flashes and 8 fast flashes, which yeah corresponds to 28 - Engine Temp Sensor.

So I guess the Engine Trouble Light does work, but not getting any fault codes or flashes when everything back plugged in.

Thanks again for the help

[WD Forte]

I'm more familiar with the Honda PGM-Fi than Yamaha
where you can call up historic faults and clear them without
any OBD readers
Not sure but I think the YBR only displays a current fault.

As you seem to have a fault occur after the bikes been running for a while, you may want to reinstall the eml and run the bike to see if you get a code when it plays up.
____________________
bikers smell of wee

[YamMan22]

Thanks for the help WD Forte, yeah you could be right perhaps this one doesn't store historical codes.

Good idea running the bike and see if a code pops up, will try this next.

Cheers

[YamMan22]

Hi

I've tried running and revving the bike for 5 mins (in my garage) and still can't get any faults to show... In fact it didn't cut out at all at high revs, but I guess this would be different when riding it... I'll have to take it up the mountain again for a test

Actually maybe I should of put it in gear and try bringing up to speed (I will try this tomorrow).

Also ordered a used TPS sensor / throttle body module, one from a WR125, it looked exactly the same I guess they would use the same part from the same factory, worth a shot for £20.

Thanks again for the help WD Forte, will post back any updates

[YamMan22]

Hi there,
Just an update, TPS module arrived today and I've tested it on throttle body...

And it does not work (not getting any resistance value changes).

So I guess either I have a duff part or the fault is on the other side of the resistor (magnet side - A). Is this possible?

I assume a magnet never breaks or loses its force and logic tells me I have a duff part but I'm not too sure.

And yes the magnet side is turning when you turn the cable mechanism.

Thanks for any help

[Nobby the Bastard]

Magnets imply a pulse rather than a resistance change.
____________________
trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Sprint ST 1050

[WD Forte]

Hmm.. if its got magnets not a VR as I wrongly assumed
then I'd hazard it's using a Hall effect shaft encoder type device
to determine the throttle position.
In my defence I dont and never have, owned a YBR
I just work on one for a guy from time to time and keep the manual here cos he'll never prise the pages open

You've got an eml now so why not just get on and ride the fecker until
a fault occurs and you hopefully get a code to point to the offending
part

Otherwise just keep spending money playing 'swap and hope'
____________________
bikers smell of wee

[YamMan22]

Hi,
Yes it has a magnet in it, ah I see not a VR then well I guess I can try the new sensor and check if voltages go up and down, will do that now

Thanks for all the help, will post back

[YamMan22]

Hi

Ok replacement sensor is now fitted and getting up and down voltages on the yellow/blue wire (closed 0v to 4v open throttle)

So it's looking like this was the fault, but I will take it for a spin soon to confirm it, thanks again for helping

[YamMan22]

Hi guys, just an update...

Took it for a spin and same problem (cutting out).
With fault code 33 (Ignition coil) now showing.

So will now look at the coil/wiring.

Edit, checked the Ignition Coil:

Primary winding resistance
2007-on YBR models 2.16 to 2.64 ohms @ 20°C
Result - 0.06 Ohms

Secondary winding resistance (without plug cap)
2007-on YBR models 8.64 to 12.96 K-ohms @ 20°C
Result - 5.38 Ohms

Spark plug cap resistance approx 5 K-ohms @ 20°C
Result - 4.98 Ohms

So looks like a bad coil, I should of checked this before however given it is a brand new (aftermarket) coil it was the last thing I thought would break

[YamMan22]

Hi all, just an update,
I replaced the Ignition Coil and the bike is now running fault free.

But ignore previous post regarding testing the coils, I did the test wrong...

Both coils show similar resistance, so it's nothing to go by... I guess when the coil heats up that is when it malfunctions

I will try putting old coil back in to see if problem comes back just to fully confirm it.

Thanks again for all the help

And for the record... The bike does store the 'flashing' fault code after dieing, as long as you don't start the engine and just turn ignition on/off/on/off/on etc the fault will continue to show infinitely... After the engine starts the fault then deletes itself.... if that makes sense