4 wire O2 sensor

[EagleMark]

Robert is exactly correct! Which could be why your overall rich. There are also some timers for Closed Loop to begin when vehicle is started, some will not go closed loop till reved up once.

But I smell HiWay Lean Cruise... = Open Loop at highway speeds...

[CDeeZ]

Fixed the exhaust leak and have been running the 4-wire O2 for a bit now and it seems to work well. I soldered all the connections so it should be foolproof!

Sorry it took me so long to post back, been busy.

Forgive my ignorance but, why exactly does RBob's lean cruise patch go O/L and how does that work I don't understand?

[RobertISaar]

lean cruise jumps out of closed loop to run AFRs leaner than stoich.

[CDeeZ]

Which must be via the "Hiway AFR" table correct?

[EagleMark]

Yes if you have installed the patch. If not it does nothing.

http://www.gearhead-efi.com/Fuel-Inj...on-1227747-ECM

[damanx]

that's why i would run the O2 sensor's signal ground to the ECM.

even if the entire rest of the ground system essentially fails for some reason, with the O2 having it's own ground reference, it will always read 100% correct. if ground isn't really ground, then the O2 voltage will shift, sending a falsely rich or falsely lean signal, depending on the shift.



my 2 cents anyways.

and i'm not sure what ECM the schematic i looked up was for, it may not have been for a 7747, there were at least 2 O2 sensor circuits i could have chosen from, both were at least slightly different.

This seemed like a good thread to revive from the dead since a related question about the 7747 case ground was in question.

I'm going to add my opinion since having read through this thread, the correct response was kind of revealed in a "beat around the bush" kind of way.

In any case, the above diagram is the correct schematic for the o2 sensor circuit for the 7747 ecm.

Essentially, if you are going to run a 4 wire sensor, AND, you want to strictly run the O2 sensor ground signal to the ECM, then you really want to use a high grade quality shielded wire. Otherwise, as Robert stated, ground the D6 wire from the ecm and then ground the O2 wire for this pin, but make sure you have a really good ground.

The schematic above doesn't really show the true circuit for the o2 sensor, but in any case, it's nothing more than a differential amplifier and the short of it is that you ultimately want the "potential" reading from the o2 sensor to be a stable reading regardless of how the ground is actually applied.

Edit to add:

If that circuit in the ecm is as I suspect, then that circuit does not care about the voltage level of the signal between o2 high and o2 low, it only cares about the absolute value between the 2 points. Maybe that is easier to understand.

[daleulan]

One thing to be cautious of when swapping O2 sensors around - planar 4-wire sensors. They are very nice in that they can light off quickly, they are faster, more accurate, and that's what most OE's are using these days. Also they are almost always ungrounded - they are designed to be tied in to the ECM sensor ground and eliminate the requirement of that (expensive) differential amplifier. The fact that National Semiconductor stopped making one of the more popular O2 sensor amplifier IC's (LM9040) is a pretty good indication that most everybody has switched over to planar sensors. But heating is critical, the heaters are modulated using a 'dewpoint' algorithm which looks at the exhaust energy and predicted exhaust system temperatures (model for exhaust pipe, catalyst, and oxygen sensor tip). The heaters are then controlled at a low duty cycle for a while then ramped up slowly to avoid breaking the sensor due to water impingement. Same applies to the LSF4.x UEGO sensors. You probably will find that aftermarket UEGO kits 'eat' sensors quite often and this is one reason why.