Twat faced CB125F o2 sensor question.

[Weisse Schlange]

Hiya

Grandsons 2013 CB125F wont run, ticks over but won't rev.

Has been going into limp mode when the o2 sensor code flashes up but clean it and the code goes but it still won't run properly.
Bogs down, just won't rev up.

Checked the fuel pump, it's fine. Spray carb cleaner in and it revs sweet as a nut.

Trying to find a delete plug for the lambda sensor but cannae find one and a new part is £110 quid.

Any other ideas, or places that supply a delete plug ?
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Hing Oan

[xX-Alex-Xx]

Looks like there’s pre-made ones online (eBay) for CB500, might be worth checking if the connector is the same and trying one of those?

Or you could chop and modify the connector from your existing sensor if you can find what size resistor to use (that’s literally all a delete plug is).

Edit: looks like 300 ohm is about the right value to use, connect across the white wires
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DILLIGAF

[Weisse Schlange]

Thanks for that.
Where did you find that info. Shouldn't be too hard to at least try to see if it cures the issue.
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Hing Oan

[WD Forte]

what code do you get?
A failing lambda sensor just affects closed loop control and shouldn't
trigger a limp mode.
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bikers smell of wee

[Weisse Schlange]

Yeh was getting code 21 but you're right, the engine should run, so I need to find out whats stopping it.

It revs clean on carb cleaner so I'm thinking fuel. The pump is pumping but is there an inline filter ?

Tried it with the tank cap off but no change.
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Hing Oan

[Hong Kong Phooey]

If the lambda signals it is rich the ECU can pull short and long term fuel trims down. This should still run though.

Lambdas don't like to be disturbed, knocking them can break them.
If the flash code says lambda then it needs attention before doing other things.

Cheap after market ebay ones do work, but your issue could just be wiring.
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'81 CG125, '97 FZS600 : '99 CBR600F4, '09 KTM RC8

[Weisse Schlange]

Been running it at tickover just now. No codes showing (soaked the o2 sensor in brake cleaner overnight)

No change. Won't rev and struggles to maintain tickover. Spray carb cleaner in the inlet and it runs like a sweetie.
It's fuel but I just don't know how.

No code is the pain in the arse. I'll end up having to strip the throttle body and test the tps.
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Hing Oan

[Weisse Schlange]

AArgghh

Ok
I started the bike with the inlet hose removed from the throttle body.
I've checked the flow right to the injector and it's fine, but when I open the throttle I'm not actually seeing any fuel spraying in. It seems like its just trying to keep running using whatever it's getting at tickover.

Fuel flow issue but not sure what. Maybe blocked injector ?

Keep throwing ideas if anyone has any

I'm narrowing it down to icv or tps.
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Hing Oan

[Hong Kong Phooey]

You can test the tps with a multimeter set to read ohms. Don't loosen the adjuster bolt just spin the throttle, usually three wires so won't take you long to work out which is which.
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'81 CG125, '97 FZS600 : '99 CBR600F4, '09 KTM RC8

[Weisse Schlange]

Fixed it.
TPS was fucked so picked up a used throttle body for £30 complete.
Job jobbed.
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Hing Oan

[xX-Alex-Xx]

[Weisse Schlange]

Braw, thanks.

No code showing at the mo after soaking the sensor and the bike is running perfect after fitting the throttle body, but I'll have a look at making up a resistor.
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Hing Oan