Injuneer

I really think there is a wiring problem, or maybe you just bought the wrong O2 sensors. But it would be unusual for both of them to be so screwed up, unless they aren't the right ones for your car. Why did you pick Bosch, and who selected the specific model #?

Injuneer

The weird thing is, when it goes into closed loop, both O2 sensors are hanging at 1.097 volts. The ECM drops the LTFT's to 108 (the lowest they can go), then starts dropping the STFT's all the way down to single digits (have never seen them go that low, in hundreds of data logs), yet the injector pule widths don't change very much at all.

At this point, I don't know what to say.

teddie300c

I used the Bosch 15703 because they were cross reference from gm 19178930

Injuneer

Look in the 1993 factory service manual at DTC 45 (page 6E3-A-78) to see if any of those conditions could exist.

teddie300c

hey guys i think i may have figured this thing out once and for all. i think the heater in one of the sensors was dead right out of the box as i cannot get 12v through the heater circuit.

teddie300c

also for the sensors i have and from what ive seen searching around on google and videos is that the sensors with the same color scheme as i have is that the 4th unused wire according to shoebox is actually needed to ground the sensor circuit. the reading on the scanner stays stuck at 1.097 unless i ground this 4th wire and then it seems like it reads as a good sensor should.

Injuneer

Strange.... Shoebox's diagram has been the “go to” for 20 years.

teddie300c

yeah and i understand that. i could still be wrong as i have my doubts but once i get another sensor ill know for sure. did you happen to look at the last scan i sent, the sensor that reads the 1.097 unless the extra wire is grounded i would really like confirmation that it is doing what its supposed to.

teddie300c

also maybe this could be a thing just for these bosch 15703 sensors. a few schematics ive come across noted that the there are the 2 heater wires and a high and low res signal. or what i think i have being 2 heater wires, a signal wire, and a signal ground.

Injuneer

Did you coat the threads of the new O2 sensor(s) with anything.... Teflon tape, etc.? Did the packaging for the sensor indicate the threads were coated with a CONDUCTIVE anti-seize compound?

Sounds like the exhaust piping is not providing the ground that the sensing element relies on for both the stock 1-wire sensors and the 4-wire sensors wired per the Shoebox diagram. Not sure how that's possible, unless there is something weird about the way the (newly discovered) headers are installed, which is a stretch.

I'll look at the scan again. At what line of data did you attach the sensor signal ground wire to a chassis ground?

teddie300c

it had a little bit of anti sieze on the threads but nothing else. i dont remember exactly but i can do another scan of grounding it on and off. one of my radiator hoses just started leaking so ill do one after it cools down enough to fix.

pretty much though if the sensor hits 1.097 the shoebox unused wire isnt grounded. i dont even remember which side it was on but only one was doing it

Injuneer

Check for a ground at the O2 sensor bung on the header collector, both sides.

I'll look at the most recent log. I ran max, average, and min calculations on both O2 sensors from the point it went into closed loop through shutdown. I don’t recall the varying values you indicate but there's a hundred thousand pieces of data in the log. I’m not on my PC, and looking at a data log of a few thousand lines of data on an iPad is extremely difficult. I'll try to get to it in the morning. That’s the best I can offer.

Injuneer

I went through the log form May 19 IN DETAIL, FRAME BY FRAME, that you attached to post #20. There is absolutely no place in that data log that either O2 sensor "reads as a good sensor should".

When you start the log, the engine is not running. Bank 1 and Bank 2 sensors appear to not be hot enough to work. Bank 1 is colder than Bank 2 and heats up more slowly. That would appear to be the one that you indicate has a bad heater, although given the apparent problems with wiring and not knowing which wires are which, I'm not convinced it's dead. Are you sure you are using the multi-meter correctly?

When you start the engine (line 114) Bank 1 is still at 0.706 Volts, and slowly warming up. Bank 2 oddly jumps to 1.035 Volts, indicating it is warmed up and working. Bank 1 does not reach full operation until line 264 when it reads 1.035 Volts, although it's still wavering slightly above and below 1.000 Volts, indicating the temperature is marginal.

After line 290, Bank 1 only drops below 1.000 Volts ONCE in 2,080 lines. Bank 2 NEVER drops below 1.097 Volts in the same period. Yes, there is some small movement on Bank 1 in the 1.0XX decimal values, but that is NOT what a functioning O2 sensor is supposed to do.in closed loop. It should produce an AVERAGE value of +/- 0.450 Volts, and occasionally drop below 0.100 Volts.

There is no way what is shown in that data log can be considered acceptable, and it is impossible to identify where you attached the ground wire, unless you feel the small changes in the 1/1,000ths position of the voltage reading is an indicator. It isn't.

teddie300c

hey i got the new o2 sensor replaced the heater circuit was dead in. im sure it was dead because i could not get 12v on the "negative" side of the sensor. you can see it from the start of this scan that the sensor sits at 1.097v until i ground the 4th "unused" wire.

Injuneer

There is no “negative” side of the heater. Either wire can be connected to 12 volts and the other to ground. Best way to check the heater would be to measure resistance. I'm not sure what you even did when you indicate you “could not get 12v on the “negative” side of the sensor”.

In post #42 I asked you to check for a ground ar the header's O2 sensor bung. That's how the 1-wire sensor gets its ground to complete the circuit. That should also work to ground the correct 4-wire sensor, eliminating the need to ground the 4th wire. Did you do that!? You asked for help, and I'm trying to help you. I don’t want to spend the time it takes setting up and reviewing another log, until you follow up on my simple request. At this point this thread is going nowhere.