Intermittent lean condition

[stephenpen]

I was out on the machine and I saw my AFR go from 11.5 to 20-30. I could not understand why.
I took the exhaust sensor out and changed it and nothing.
Randon lean mostly off throttle. I was trying to figure out how to check the donuts and I noticed a loose hose clamp on the main fuel line.
Tightened it up and my AFR is perfect again. I was thinking of installing a fuel pressure gauge but I alway go over board with all the gauges. Maybe I should. What is stock fuel pressure
Now I wonder what else could be loose or not done right.

 

[mbarryracing]

What AFR gauge are you using? Some don't even read that high. I thought that maybe the engine wouldn't even run, that AFR wouldn't support combustion.
Just FYI, a cylinder misfire or fuel cutoff / rev limit will cause a misleading lean spike because the unburned air / oxygen gets passed right into the exhaust... gets read by the sensor.

 

[stephenpen]

What AFR gauge are you using? Most don't read that high.
A cylinder misfire or fuel cutoff / rev limit will cause a lean spike because the unburned air / oxygen gets passed right into the exhaust... gets read by the sensor.

I was suprised to see it read that high too.
Its a prologger

 

[stephenpen]

It would only flash 20+ for a second. It was like the fuel line sucked air for a split second.

 

[mbarryracing]

Did the engine stutter or stumble? The sensors don't react that quick, especially since it takes a 1/2 second for the mixture to enter the exhaust stream and travel to the sensor...

 

[stephenpen]

You could hear a stutter at the same time the gauge read high.
I was only going 30kmh ish at the time and turned back right away.

 

[rxrider]

Idle fuel pressure is 36.3 psi/lbs or 250kPa.

A fuel gauge is great for tuning purposes, I have one I connect whenever I need to check fuel pressure.

 

[NYTRORYDERAK]

I have been haveing a similar issue with my super and prologger set up. Sometimes at wot my AFR will spike all crazy up to like 30 of 40(crazy right i figured it would of poped the motor that high) then if i chop the throttle for a second and get back on it, it will be normal again. It has been doing it off and on for the last two rides. I inspected the exhaust system and found some cracks in the header pipe before the o2 so I welded them up and hoped that was it. Next ride same thing. Sled runns great and never misses a beat so I am thinking it is a o2 starting to go out. Any other ideas??

 

[mbarryracing]

Does it do that after a constant throttle cruise? What was the AFR reading before it all full of a sudden spikes to 30-40? Might be heat related, a sensor frapping out.. Especially if you don't feel or hear the engine bog or stumble at that moment, then it's likely a false reading.

 

[NYTRORYDERAK]

Ya it seems to happen when boondocking after a bit of wot. Never felt anything different with the way the sled was running. Afr's is about 11.5 at wot no matter how long i hold it there. Sometimes it might dip a bit to around 10 but most wot pulls are right around 11.5. I have been trying to get a good look at the gems when this happens and it stills shows that it is fueling in the red mode when the afr's go all crazy so I believe that the contorller is still working. Exhaust dought nuts are shot maybe? o2 on the way out?

 

[mbarryracing]

Heat wreaks havoc on electrical components, 02 sensors are not immune. An exhaust leak wouldn't change so drastic so quick.
Try a new sensor...

 

[DooAssassin]

The lean spikes could be from raw fuel hitting the O2 sensor, its a faultily reading. This happens if the sled misses or hits the rev limiter. I had this happen before also, scared the out of me. I know it should do the opposite but ive found it show lead momentarily. Maybe thats whats happening with your sled.

 

[mbarryracing]

Stock rev limiter is a fuel cut type, so no raw fuel from that...
A misfire, yes.

He had mentioned the sled doesn't miss a beat, but could be happening un-noticed...

 

[rxrider]

Raw fuel will make the AFR read 20.9 for most systems, that equals to full lean. A higher reading is most likely caused by heat, faulting sensor or an electrical condition. At full lean your engine will not run.

 

[MOUNTY]

I have learned that all gas is not the same, I seem so be a sucker for high octane and would fill up at a certain gas station whome would have 94 octane. When I fill up at this place, my fuel air ratio is all over the place and lean. If I fill up at any other place with 92 octane, my fuel air ratio is bang on to where it should be. I run 5-7Pds. of boost at any given time unless I go to the mountains.
Mabee try a different gas than your usual. I know we all have our favourite places to buy gas, but what is good for our sleds sometimes takes residence.