earl's_f20c

I'm trying to get to the bottom of my annoying hesitation/kangaroo problem so purchased an OBD2 display (Ultragauge My link) so I could see what the sensors were doing.

The primary o2 probe values seem to jump all over the show compared to the secondary, but as I'm no expert I'm not sure how to interpret the data

Obviously, when I'm observing these changes the running conditions are stable, stable revs, load etc.

It jumps around anything from 0.000v to 0.915v then back to 0.215v for example just at a steady idle.

Am I correct in thinking that when in 'closed loop' mode the engine fuleling is based on the feedback from this sensor? (amongst others of course). Wondering if it's the culprit I'm looking for.

Any help welcome!

nb: Heatsoak, although a real problem for S2000's is not the cause here as it happens on the way to work after 5 mins, when the intake temp is cold.

s2konroids

In partial throttle yes should jump around, wot no.

earl's_f20c

Thanks s2konroids, but if I could just pick your brains a bit more...

How about when at a steady idle? I thought that 0.2v is lean, but 0.8 is rich so is my ECU 'hunting' to find the pefect mix all the time and failing miserably?
I know I'm probably a muppet but surely if conditions are stable the reading shouldn't vary wildly.

Cheers

mrgrumpy

just had mine diagnosed as faulty[now fixed],the vehicle electrician showed me a picture of how the sensor should work on the oscilloscope.it should fluctuate between 0.1v and 0.9v at regular intervals[basically up and down between those two values].

earl's_f20c

Mmmm interesting, cheers Mr Grumpy.
Can I be nosey and ask what your fault was/symptoms were etc? Always interested to learn a bit more...

Si2k

You need a scope on it. The ODB port wont be fast enough to be able to diagnose any issues

MB

This is correct - the most efficient way for the ECU to achieve the right AFR is to bounce around, effectively.

Being lean / rich for these short periods if fine, and how all car engines work.

It bounces faster at cruising speeds.

MB

If you know what you are looking for, and OBD or reading direct from the sensor can be useful, but if you do see odd readings it could be a number of things.

For example closed loop fuel control doesn't just take inputs from the lambda sensor, it will also look at coolant temps and MAP / MAF readings. If one of those sensors is screwed, this will influence the AFR reading. So you often don't know if it's chicken or egg.

earl's_f20c

Yes, looks like it works in a completely different way to how I expected! I do have a digital storage scope at work so that would be useful to check the frequency of the waveform.

Don't know which direction to go now though as I've been through all the FAQ's, cleaned IACV, MAP sensor, throttle body, had valve clearances done properly, eliminated heatsoak yet it still happens, which is why a varying value looked like a culprit, oh well, the quest continues...

MB I agree, the reader was only $60 from the states and has at least let me see into the cars' brain. So far all the values check out though, so thinking cap on!

mrgrumpy

car would start and idle as normal,but would not allow me to pull away,revs would drop to almost cutting out levels.after two or three minutes the car would be fine until it decided to play up again.i have had some kangarooing issues so i am hoping this will be sorted