PC III and O2 Sensor Question

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Gitbox

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The Power Commander III USB installation manual does not mention disconnecting the O2 sensor. In fact, it doesn't mention the O2 sensor at all. I have read that it needs to be disconnected for the PC III to work correctly, but would that not generate an error condition? The ECU has codes for improper O2 sensor operation and since the PC III goes between the ECU and the injectors and not in line with the O2 sensor, how is it that no error codes are generated with it disconnected? I tried asking PC III tech support, but they did not even know the FJR has an O2 sensor, so they were no help at all.

 
No, No errors. No need to spoof anything like on other more complicated platforms

The FJR ECU is a very simple one. It cares not if it sees an O2 sensor.

Works fine... lasts a long time.

 
Why do you have to do this?

It seems counter intuitive to me as well.

Inquiring minds want to know how the computer adjusts A/F ratio without the only input that tells it what the A/F ratio is at the current moment.

If it works, and it obviously does because many have run the PC on early FJRs for years, don't F.... With it, but Why?

 
The ECU generates fuel injection signals of a particular pulse width to control fuel quantity, and thereby controls the intake mixture. It does that by monitoring a bunch of different sensors at all times. The ECU operates in two modes: Open loop mode or closed loop. In the default open loop mode the ECU pays no attention to the O2 sensor, therefore the injection time is dependent only on the base map program and all of the other sensors.

Under limited circumstances the ECU will switch to "closed loop" mode. Those are when the bike is either idling or under steady throttle (cruising), and after the O2 sensor has warmed up enough to output a signal of the "proper voltage" range.

During closed loop mode the ECU will trim the injection duration based on the O2 sensor's feedback to achieve the target A/F ratio that creates the desired O2 level in the exhaust stream. Before the O2 sensor has warmed up, or if it has been unplugged, the ECU just never goes into closed loop mode, so it relies on the base map program and all of the other sensors.

The Power Commander simply adds or subtracts time to the fuel injector signal pulse width from the ECU, based only on it's own input parameters., to add or subtract fuel to the mixture Those input parameters are just the engine rpm and the throttle position. If the O2 sensor were still connected and the ECU went into closed loop mode, any time added by the PC would be subtracted back out by the ECU as it attempts to achieve the optimum O2 signal feedback.

In other words, the ECU and PC would be fighting each other, or canceling each other out and you would have no benefit from the PC when the ECU is in closed loop mode. The way to prevent that from happening is to disconnect the O2 sensor.

Nobody really cares much about the mixture at idle (except the EPA), but one reason to run a PC is to eliminate the "lean surge" condition during steady throttle cruising. If the O2 sensor is plugged in the PC will not be able to eliminate that. It will still work at all other times, because the ECU is in open loop mode, but won't rectify lean cruise surging.

 
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Thanks for the responses, guys.
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Queensland: the installation instruction page that you referred to is for Gen II FJRs, mine is a GEN I and those instructions make no mention of an O2 sensor.

Fred: excellent description of ECU fuel control! The problem I was wondering about is that the ECU diagnostics have codes for improper operation of the O2 sensor, so why are no codes generated when it is disconnected?

What I am going to do is unplug the O2 sensor (PC III removed) and see if a code appears. If it does not, then the diagnostics are incorrect in the service manual because it should give a code 24.

24:
No normal signals are received from
the O2sensor.
• Open or short circuit in wiring harness.
• Defective O2sensor.
• Malfunction in ECU.
• Improperly installed sensor.
 
Nope, it won't. I ran my 1st Gen with the O2 sensor unplugged for many years, as do many others. No codes. The FJR ECU is a fairly crude affair.

 
Strangely enough, the O2 sensor may cause a code if the A/F is out of the range the ECU can set but doesn't cause an error if it is missing entirely!

 
I kind of thought this was the situation but thank you Fred for your excellent explanation.

Much less stringent controls than on a current automobile

 
I guess I'll have to throw a scope on the sensor and see if it ever enters closed loop mode. I am assuming of course that the trace should look like a car's O2 signal. I might add some propane and a vacuum leak to see if the sensor responds correctly. It'd be so much easier if the bike was OBD II compliant.
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Ross: Odd that the ECU would care if there was a too lean or too rich condition, but not care if the O2 sensor was missing. Very weird.

Hah! Maybe that's why the PC III instructions omit the O2 sensor completely. If the ECU doesn't care, why should it?
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Not that it matters but my 03 has run close to 100k with the 02 sesnsor plugged in and the PCIII installed. It was installed that way and set up on the Dyno by a factory dynojet tech. It cured all the lean surge at low and cruise speed. I don't profess to know how the damn thing works but it does well on my bike.

 
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I tried it both ways on my '05 and there was a marked difference (for the worse) in the lean surging with the O2 plugged in, so I left it unplugged.

 
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Still investigating this but I did find why there is no mention of the O2 sensor in the GEN I FJR PC III installation instructions. The wire to the O2 sensor is intercepted in one of the wiring harness connectors so the disconnection takes place inside the PC III, therefore leaving the O2 sensor connected or not makes no difference with GEN I PC III. I'm sure the wiring is different with the GEN II FJRs and I'll bet the O2 sensor is not intercepted.

 
Still investigating this but I did find why there is no mention of the O2 sensor in the GEN I FJR PC III installation instructions. The wire to the O2 sensor is intercepted in one of the wiring harness connectors so the disconnection takes place inside the PC III, therefore leaving the O2 sensor connected or not makes no difference with GEN I PC III. I'm sure the wiring is different with the GEN II FJRs and I'll bet the O2 sensor is not intercepted.
Wow! I have unplugged the O2 sensor in my '04 because Dynojet said to. I would be interested in reading the article about the Gen I and Gen III O2 use. I know the PC III reads the TPS signal, didn't know about the O2 sensor, I thought it was unplugged to keep the ECU from going closed loop.

 
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I don't think the PCIII disconnects the O2 signal for a couple of reasons. I think it has a pass through on the signals that it doesn't use, including that one.

While the O2 sensor signal does pass through that cable connector (on both Generations), I recall that DynaJet specifically informed me to disconnect the O2 sensor. even though it isn't in the 1st Gen's installation instructions.

When I did re-connect the O2 sensor on my 1st Gen as an experiment I'm fairly sure that it started surging again, though it was quite a while ago.

Also, there is a "street legal" version of the PCIII that does require the O2 sensor to remain connected, but I suppose the wiring for that one could be different.

It would be pretty easy to ring out those pins with an ohm meter and see if the signal gets passed thru

 
Good points Fred.

I think I will check the wiring harness and see if the O2 wire does pass through.

 
In my case, adding the O2 fooler with PC-V caused the ECU to start running leaner and leaner until it was absolutely unrideable in the closed loop area. If I reset the adaptives by disconnecting the battery, the bike ran great, then started to run worse and worse again.

It took a couple of hundred miles to get to be unrideable. It is surprisingly hard to run a 1300cc bike outside the Open Loop area to get home!

My theory is that the O2 fooler was somehow giving the ECU a slightly rich signal and it was adjusting to try to get back to where it wants to be.

 
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