New to this platform. So the car is supposedly a tuned 383 stroker. The car has long tube headers with the downstream sensors tuned out (square plug). Sensor wiring got destroyed loading onto a trailer. When looking into why the car was running bad i found I'm guessing what looks to be a resistor and maybe a diode not exactly sure soldered inline in the wiring. I have a new sensor on the way I'm just wondering what route to take and if there is a plug n play setup I can order in its place.

 

Hard to identify those wires.

Since you indicate you have after-cat sensors, you must have an OBD-2 1996 or 1997. The after-cat sensors have little, if anything with how the engine runs. If they are "tuned out", no need to replace the damaged sensor. It's only purpose would be to plug the bung in the exhaust pipe.

And if the after-cat O2 sensors are "tuned out", wiring would not seem to be required, unless maybe the heater circuits,

Have you scanned the PCM for codes? Again, tuned out, the sensing circuit should not set a code.

Looking at the wiring diagram in the 1996 factory service manual (essentially same as 1997) the four wires to the after-cat sensor are black, pink, (heater circuit), and tan and purple (sensing circuit). There is no gray wire involved, so it's hard to tell what wires they were even working on. Are these part of the wiring to the O2 sensor connector? Typically with long tubes, harness extensions are required. Are these wires part of an extension?

Did they do the same mod on the after-cat sensor on the other side?

 

They extended the harness and wired this resistor into the flat plug with a heated sensor ac delco afs 97 is the sensor #. The square plug is not plugged into anything. Thank you for your reply and time.

 

Your description completely lost me on what wire on what sensor had this modification.

Been here for 27 years and haven’t seen anything like that before. Maybe someone else can pick this up. Might take a while, since not many people follow this site any more.

 

I am right there with you. I don't get why they changed the plug from the square plug to the flat plug and also wired in the resistor and diode. If that's what it is. All I know is the car ran great idled and throttle response was very responsive before sensor wires were ripped out. Idk what else to do other than hack up an expensive sensor and add this back in or get it re-tuned afterwards. I was just hoping someone would know what kind of hackers i was dealing with. I ordered the same sensor but they have the square plug. I got a conversion plug from Michigan motorsports to convert from square to flat plug then u guess in going to wire in the resistor and diode on 2 of the wires.

 

The pre-cat sensor may have failed, so they took the unused sensor out of the after-cat position, necessitating the change to the square connector on the pre-cat harness. The sensors for pre-cat and after-cat are identical part #, only the connectors are different. But the diode/resistor hack serves an unclear purpose.

Let me see if our electronics guru can look at this.

@GaryDoug

 

Found this…. see post #4 and following.

https://www.ls1.com/forums/showthread.php?t=8950

Apparently this is some kind of hack on the after-cat sensor, to dampen the voltage swings to the extent they don't trip the SES light. More evidence to suggest someone just moved the after-cat sensor up to the pre-cat location. Surprised this didn’t cause issues, and an SES light. Does the SES light come on during bulb check when you turn the key to “RUN”? Maybe someone pulled the bulb??? You need to scan for codes.

 

Describe exactly how this resistor/capacitor is or was wired. Where does the wire from the resistor go...to the sensor or to the car wiring? I am asking about the grey wire going to the right in your photo. That is a low pass filter (resistor and capacitor) that changes any input signal from high frequency to lower frequency. I have a feeling that went to a square wave generator which signal is then changed to more of a sine wave signal, so the pcm could more easily read it as an o2 signal. I used a very similar filter (100k and 4.7uFd) in my pcm test rig to change a signal from a little (555) square wave generator to an O2 output signal. A possible use would be in the downstream O2 sensor circuit to simulate a good signal there.
https://www.eleccircuit.com/simple-5...rator-circuit/

 

I think you are right. The previous owner just swapped the rear o2's to the front not knowing there was a resistor and diode wired in and just changed the plug from square to flat. Because it looked like there were 2 different sets of wires used. So using new sensors for both sides moving forward what do I need to do?

 

it is in-between the plug and the sensor. Any suggestions from you guys would be great ive got new sensorels on the way and square plug to flat plug conversions from Michigan motorsports. Do I still need to wire in the resistors. I'm not very tech savvy. But I can solder in those wires if need be.

 

Which way does the grey wire end go... to the car or to the sensor.? I suspect it goes to the car. Remove both the resistor and the capacitor. They have no purpose now.

 

I suspect it goes to the car to send back a lower voltage or show resistance. The wires were ripped out of the sensor and I had cut the plug off to reuse on the new sensor and was going to use those wires to extend my sensor and found the resistor if that is what it is I'm unsure of the correct terminology. I'm going to just try it without and see if it works parts wont be here till Monday so I will let you guys know what happens. Thanks you guys both for your time I really appreciate it.

 

https://www.paladinmicro.com/MustangMILEliminator.htm

 

So it's a DIY replication of an O2 sim (the thing they outlawed, to put Casper out of business)?

https://www.epa.gov/enforcement/casp...-clean-air-act

 

yep..sorta. I think Caspers device was an active signal generator that did not need the o2 sensor to be installed. Different technique, same result.