PCM Output Voltages - O2 Sensor Issue Diagnosis

[Cincinnatus]

If running on one bank, it would be so obvious.

[evilstuie]

If running on one bank, it would be so obvious.

Well it seems obvious by the fact the engine is not producing any heat on that side and the O2 readings are showing no fuel.

I've tested both injector banks for power which they both have.

[Cincinnatus]

Is it running on 4 cylinders? It would run terribly. Injectors are ground switched. Check for injector pulse with test light. Pull plugs to see if wet. Good compression? Basic diagnostics before blaming O2 or PCM.

[Charlescrown]

You don't need a noid light a 12 volt test light will do.

[evilstuie]

Is it running on 4 cylinders? It would run terribly. Injectors are ground switched. Check for injector pulse with test light. Pull plugs to see if wet. Good compression? Basic diagnostics before blaming O2 or PCM.

For maybe the fourth time now, I know the injectors are constant 12 volt and grounded by the PCM to actuate.
A noid light is a test light but it has the correct resistance filament to light up and not cause damage to the PCM which the normal test light can do.

I appreciate the effort guys, but the expertise and specific information I need to diagnose the PCM, or eliminate it from the root cause is not here.

I can't fit a compression gauge in with the headers the way they are designed without removing all of the exhaust and my back is not letting me get under the car to remove it all at this stage.

[Cincinnatus]

It's unfortunate that my 35 years as a mechanic aren't enough expertise for you. A test light will not damage the PCM as I've used one many times. Compression you can tell by cranking without starting. I've never heard no heat from one side of an engine as a complaint but I've had a dead bank and knew it immediately. Just trying to help you out since you aren't finding the problem using your diagnostic process.

[kojab]

Hey guys,

I've been chasing some answers to this on a few forums but no-one seems to know.

I'm chasing some electrical gremlins in my 0411PCM LS1 swap into an 85 TransAM and need some help with what I should be seeing on the O2 Sensor wiring.
These are using the flat black 4 pin O2s for Bank1 & 2 pre cat, no second sensors, and I have a wideband for tuning on left exhaust only.
When I log in HP tuners when the car fires up, my left o2 is sitting around 0.1v-0.3v and the Wideband is completely lean (20.0), the right side is sitting on 0.448v with a bit of a twitch but doesn't move. ( suspecting it could be dead)

Here's the thing though, the right side is nice and hot at the exhaust side, but the left side I can grab onto after a minute of the car running and it's only slightly warm, like it's not even firing.
I checked all the coil wiring and injectors for correct voltages, 12v where it should, ground on the coil pack, and about 430ohms on the control wires.

I got down to the O2 sensors and got these readings:

Left side:
Pin A: 4.4v
Pin B: 1.26v
Pin C: GND
Pin D: 12.4v

Right Side:
Pin A: 4.4v
Pin B: 1.26v
Pin C: 12.4v
Pin D: GND

I was told the heater pins C&D don't matter with polarity, but as far as I know Pin A is meant to be low reference so I was expecting something of a 0v / GND continuity situation and Pin B is High which I expected would be 1.0v.

Is anyone able to confirm what voltage should be outputted from the harness when the O2 sensor is unplugged?

Also, I find it strange with all the DIY work done on these and custom harnesses that no-one has ever put together a table with the PCM pinout that includes the expected voltage outputs, inputs and resistances so you can do a complete check of your harness and PCM prior to firing up...
I'm putting one together as I test everything, but it seems pointless while I'm still having issues, as I won't know what's correct and what is giving bogus readings due to wiring issues/ stuffed PCM.

Any help as always is appreciated.

Had a closer read of your first post.

Possible scenario.

You say "When I log in HP tuners when the car fires up, my left o2 is sitting around 0.1v-0.3v and the Wideband is completely lean (20.0),
the right side is sitting on 0.448v with a bit of a twitch but doesn't move. ( suspecting it could be dead)

1) When you say the car fires up, I assume its running an all 8 Cylinders.

2) You are logging with 2 sensors on the left hand bank with HP tuners. Lets assume both sensors are working correctly.
Your left o2 is sitting around 0.1v-0.3v and the Wideband is completely lean (20.0)

O2 0.1v-0.3v would indicate that the sensor is working and is also inline with your Wideband (20.0) both reading lean
probably due to both sensors not reached normal working temperature.

3) You say "right side is sitting on 0.448v with a bit of a twitch but doesn't move".

Looking at your O2 Pinouts above it appears the Right Side O2 is not wired correctly. With no 12 volt voltage on Pin D
you would normally be reading the output of the PCM being 450 mV which you are seeing.

4) You say "right side is nice and hot at the exhaust side, but the left side I can grab onto after a minute of the car running and
it's only slightly warm, like it's not even firing.#

I would look at possibility of one of the Cats has collapsed.

Left side:
Pin A: 4.4v
Pin B: 1.26v
Pin C: GND
Pin D: 12.4v

Right Side:
Pin A: 4.4v
Pin B: 1.26v
Pin C: 12.4v Incorrect
Pin D: GND Incorrect

[Cincinnatus]

Kojab, if pins c & d are O2 heater, polarity doesn't matter as it's just a heating resistor. He said he has headers, so prob no cats, but it is a possibility.

[kojab]

Kojab, if pins c & d are O2 heater, polarity doesn't matter as it's just a heating resistor. He said he has headers, so prob no cats, but it is a possibility.

Yes I understand the heater circuit but best to put the wiring where it should be. People do strange things with wiring. One never knows what problems can arise if some where else in the loom has been modified for what ever reason. As you would know the 12 supply to the Oxygen sensors go to other sensors and modules.

[evilstuie]

Kojab, if pins c & d are O2 heater, polarity doesn't matter as it's just a heating resistor. He said he has headers, so prob no cats, but it is a possibility.

Yes I understand the heater circuit but best to put the wiring where it should be. People do strange things with wiring. One never knows what problems can arise if some where else in the loom has been modified for what ever reason. As you would know the 12 supply to the Oxygen sensors go to other sensors and modules.

Hi Kojab,

Cats are installed, not sure how long it takes to clog one, but I'll check it out.

I borrowed a mates noid light set and had signal on 1 and 3 but only testing one at a time, i was only getting it light up once or twice in 4 or 5 seconds of cranking.
I have a 3HP torque reduction starter so it kicks over pretty qcuick.
My mate also had a different style compression gauge that fit in between the headers.

I did a compression test in the little time I had this afternoon on cylinder 1 and 3.
It was cold but had 180 and 175.
Heads are 241 higgins cnc ported with 30thou shaved off and a VCM710 cam which is around 232/234 from memory.

Cylinder 1 spark plug looked like it had never fired, motor has run in total for probably about 6-7 minutes since build.
Cylinder 3 spark plug was black and wet.

I tested both out of the cylinder though with an alligator clip to earth it and was getting spark on both.

I'll check #5 & #7 tomorrow, but it's just getting stranger.