That's what the transport delay is, it's the time the ECU allows before it re-reads the lambda information after a correction, if this isn't correct the ECU can get into a state where it's "chasing it's tail".
As has been said above, it should be fine in the collector area as this is where it is on cat cars - all these are 3 or 4 wire heated sensors though. On my 16V ibiza, I have a 4-1 tubular manifold and have a 4 wire sensor in the collector area - for clearance I had a small 90 degree bend put in with a lambda boss on the end - now the lambda runs parallel to the collector but the sensor is right at the end so can still snifff exhaust gas. My ecu does not need a lambda to work but I have an air/fuel ratio guage in the car that uses the lambda - and it works a treat. So I would stick it in the main pipe or collector if I was you Cheers Rob
Just to repeat what I said earlier, probe placement is dependant on the ECU rather than being generic.
The ECU does basically sample the voltage and correct accordingly. If it sees a low voltage for a set time it takes steps to richen the fuelling, and vice-versa. If you had two sensors both showing rich or lean at the same time, there wouldn't be much problem. It's when you're close to stochiometric and they're both oscillating that the problems occur. At each extreme you'd have either totally destructive interference, and the ECU would see a false lean signal, or constructive interference where the ECU would see rich. In reality you'd be somewhere in between and the ECU could be seeing anything. The other potential problem is that the sensors aren't powered, they're generating the voltage themselves so they need to be feeding something with a suitably high input impedance.
I understand what you're saying about one sensor reading high and one low but surely wouldn't that be the point, so the input signal is an average across 2 or 4 cylinders? I'm much better with engines than circuit boards, but would'nt you need a low impedance with such a low output voltage?
But the ECU is expecting to see a fairly clean square wave signal at around stochiometric mixtures, and it's control strategy is designed around that input. Adding together two different square waves with likely different phases and frequencies will produce a fairly random output, with similarly random effects on the ECU. Have a play with this, it uses sine waves but you'll get an idea of how messed up the combined output is getting. A low impedance will try to draw too much current, which the sensor isn't able to provide.
I've played with the wave interference thing and I understand what you mean but for that to happen wouldn't the probe output have to be AC or at least modulating (if that's the correct term)?
You wouldn't get totally destructive interference, but you will get the same shape of waveforms, just centred around 0.5v.
Yeah but if I understand the way the ECU samples the the voltage it's not constantly monitoring the output voltage, it just takes an instantaneous voltage reading and compares it to the table. I'd have only thought waveform distortion would affect a continuous reading
The sensors response time is not that quick, its response time will average the exhast pulses to give a smooth signal to the ecu. Typically taking at least a few engine revolutions to update to a new oxygen value.
The problem there is that the response of a sensor is such that if the ECU were to sample a voltage of around 0.45V, it could map it to quite a wide range of AFR A google trawl also found this info, basically most ECU's will assume the sensor is not ready if they read ~0.45V from it.
Maybe I'm being thick but I don't get this at all, here's the chain of events as I see it. ECU thinks, oww best check the lambda voltage. ECU get's out it's voltmeter and measures voltage. ECU thinks oww that was 0.86V that's a bit rich. ECU removes X unit from the base fuel map figure. ECU leaves it X ammount of time. ECU get's out it's voltmeter and measures voltage. ECU thinks ahhh 0.47V, within spec. ECU leaves it X ammount of time, then starts again. I'm not taking the piss just trying to simplify why I don't get your wave distortion thing.
Me again (sorry to butt in ) Just been reading up and it says it`s possible to kill an o2 sensor by having it too close to the port (overheating), would my stainless (and wrapped) runner cause the gas inside to be noticably hotter than the normal G60 setup? Also it says the heated lambda`s are best sited at the collector, but due to the ecu and distance from the ports I can`t see this being an option, plus the ecu expects it to be 1.5ft from the port? Has anyone killed a lambda sensor though heat?
OR... ECU thinks ahhh 0.47V, the sensor hasn't warmed up yet ECU ignores the sensor for a while. Which admittedly probably wouldn't be the end of the world, as it's likely to be happening around stochiometric so correction isn't really needed anyway. But it's still not functioning correctly
But why would the ECU think the probe wasn't ready just because it returns an acceptable voltage. Please tell me if I need to go away and get a degree in electronics
Keith, to go back to your original question with a tubular steel manifold wrapped at least to the back of the subframe your original suggestion of just after the collector sounds good
Cheers, if there`s room I`ll stick it near the collector, wrap right up to the sensor to keep the gas nice and warm Just read this off the link, A fully warm O2 sensor *will not spend any time at 0.45 volts*. In many cars, the computer sends out a bias voltage of 0.45 through the O2 sensor wire. If the sensor is not warm, or if the circuit is not complete, the computer picks up a steady 0.45 volts. Since the computer knows this is an "illegal" value, it judges the sensor to not be ready.
The wave distortion thing is not relevant. The oxygen value is just fluctuating between two values, as opposed to sitting at the 0.47V, which you may have expected.
I actual start to get how the sensor works now, sniffing oxygen, best to be monitoring all 4 cylinders I think as it wouldn`t take long to melt a piston (although it isn`t active at WOT?).
