No check engine light when disconnecting O2 sensor - Bad fuel consumption

danIstrate

New member
Hello everyone,

As the title says, I've been having bad fuel consumption for the past 6 months.

It all started in autumn / fall when I started seeing an increase in fuel consumption.
In the beginning, it was 1L more / 100km so it was not that bad. It peaked in December when I reached 11L/100km or 22mpg.

Until now I checked compression, valve clearances, connections, changed plugs to iridium and verified the gaps, checked coils cold and hot.

Last thing I did I measured the O2 sensor and it has showing no continuity. I changed the O2 sensor.

But there is a problem. If I disconnect the O2 sensor, no check engine light pops up.

I'm looking for an explanation. Does this mean there's something wrong with the ECU and it practically ignores / doesn't see the O2 sensor ?

Any advices on what to check related to not popping a check engine light when I disconnect the o2 sensor ?

Thank you!
 
Could the ECU been flashed before to ignore the O2?
And now one or more injectors gone to shit and ooozing fuel into it.
Any dynos nearby?? a quick A/F measure should not cost an arm and a leg......
Have you checked the ECU on the bike, many put a sticker on em after flashed....
 
Update:

I took the connector out and did some riding, including city, highway and all out flooring it and still did not pull a code.
 
Could the ECU been flashed before to ignore the O2?
And now one or more injectors gone to shit and ooozing fuel into it.
Any dynos nearby?? a quick A/F measure should not cost an arm and a leg......
Have you checked the ECU on the bike, many put a sticker on em after flashed....
Sorry, your reply popped out after posting the comment.

This will most likely be the problem.

After it stops raining, I will pull the ECU and take it to someone to see if it's been flashed.

I am also betting on some injectors being clogged because I've been to Greece last summer and fueled in some shady gas stations, so suddenly, clogged injectors don't sound so far fetched.

I will keep you posted nonetheless.

As a last simptom that's new, yesterday it didn't start on first, second or third try.

It only started after cranking and giving it 50% throttle. So, in my opinion, it's pointing into some fueling direction.

We'll see.
 
....also, when you get it started and rev it....
If it revs and hit the idle at a millisecond it should be on point......if it dips and then hits the idle it would be fat as fekk......other way if you rev and it hunts up there before idle it should be lean......
 
Hello everyone,

As the title says, I've been having bad fuel consumption for the past 6 months.

It all started in autumn / fall when I started seeing an increase in fuel consumption.
In the beginning, it was 1L more / 100km so it was not that bad. It peaked in December when I reached 11L/100km or 22mpg.

Until now I checked compression, valve clearances, connections, changed plugs to iridium and verified the gaps, checked coils cold and hot.

Last thing I did I measured the O2 sensor and it has showing no continuity. I changed the O2 sensor.

But there is a problem. If I disconnect the O2 sensor, no check engine light pops up.

I'm looking for an explanation. Does this mean there's something wrong with the ECU and it practically ignores / doesn't see the O2 sensor ?

Any advices on what to check related to not popping a check engine light when I disconnect the o2 sensor ?

Thank you!
Check the plugs. Is one wet? Check the injectors. A leaking injector can burn a hole in the piston. You can also test the injectors in the diagnosis mode.
 
...It peaked in December when I reached 11L/100km or 22mpg...

Interesting! Mine has been getting similar performance, only I thought this was normal since it's been this way since I bought it (used). It struck me as odd at first, but I figured that this FZ8 was bound to burn more than my R6. Still... ~150km per tank is low right? It has a slip-on exhaust and pops like crazy when I decel; obviously running rich.

I'd been considering putting block-off plates and a PAIR system eliminator to get rid of the popping. Speaking of which... has that been done to your bike by chance? That could be another reason that unplugging the O2 sensor doesn't shoot a code.
 
Hello, everyone.

Check the plugs. Is one wet? Check the injectors. A leaking injector can burn a hole in the piston. You can also test the injectors in the diagnosis mode.
Plugs checked a lot of times, in the end replaced them with iridium. None of them wet.

Injectors pulled out, tested manually, all of them in working order. 12.5 Ohms resistance on all of them.
Cleaned them with carb cleaner multiple times, blown them backwards with an air compressor, cleaned them again. Spray pattern didn't seem off when I first cleaned them.
Nonetheless, sticked them back in. Bike seemed to run a little bit better first then as soon as it reaches temp, the RPMs start oscilating again.
There's been some improvement to how the bike's running but I haven't had the time / mileage to do a Fuel consumption test again.

Will do it pretty soon to see if there is any improvement.

Interesting! Mine has been getting similar performance, only I thought this was normal since it's been this way since I bought it (used). It struck me as odd at first, but I figured that this FZ8 was bound to burn more than my R6. Still... ~150km per tank is low right? It has a slip-on exhaust and pops like crazy when I decel; obviously running rich.

I'd been considering putting block-off plates and a PAIR system eliminator to get rid of the popping. Speaking of which... has that been done to your bike by chance? That could be another reason that unplugging the O2 sensor doesn't shoot a code.
I don't know if it has some kind of eliminator, I haven't seen it / something like it while tearing it down and trust me, I have teared it down too many times.
I have found no signs of tampering with the electrical wiring.

I will get back to you if I see some changes or if I ever find out.

But I am very tired of this issue and frankly, I'm tired of this bike. Too much time, money and sweat invested into it and even if I find what the problem is, I don't know if I can enjoy it anymore.
I've been looking into selling it and buying a CFMOTO 800MT but now's not the right time.

If I ever find out what's wrong with it, I will let you guys know.
 
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