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Discussion Starter #1
Hey all,

I have a 1990 GT that is running very rich and seems to stay in open loop. I had a shop verify that the Bank 1 02 sensor is reading 0.0 volts at all times. I've verified my grounds, resistance values of the ECM harness and pin 46 of ECU, replaced the passenger side O2, and replaced the O2 harness. TPM and MAF appear to be functioning as they should, but MAF voltage at idle seems a little high... Around 0.9-1.1V. Is there anywhere else I could look or any potential causes that could be causing the 0 V reading at the sensor? FPR appears to be functioning well too.... Just scratching my head over this one...

Forgot to mention that the bank 2 O2 sensor is working properly...
 

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What is pin 46 of the ecu?
Do you have a electrical diagram showing the o2 sensors and pin out to the ecm to post?

I would maybe check continuity at the pin on the ecu that goes to the 02 sensor in question and to ground (Guessing without looking at the diagram). Do this with ignition off. Your looking to find out if you have a complete circuit.
If continuity is infinite, you have a break somewhere in the circuit. If you are seeing zero resistance, you have a short in that circuit somewhere.

Either do above, or check voltage at the wire right at the ecm (whatever pin number and wire colour that is) that goes to the o2 sensor while the vehicle is running. Any voltage there?
 

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Pin 46 is a signal return gnd for your TPS, ECT, ACT, egr, and BP.
 

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Hey all,

I have a 1990 GT that is running very rich and seems to stay in open loop. I had a shop verify that the Bank 1 02 sensor is reading 0.0 volts at all times. I've verified my grounds, resistance values of the ECM harness and pin 46 of ECU, replaced the passenger side O2, and replaced the O2 harness. TPM and MAF appear to be functioning as they should, but MAF voltage at idle seems a little high... Around 0.9-1.1V. Is there anywhere else I could look or any potential causes that could be causing the 0 V reading at the sensor? FPR appears to be functioning well too.... Just scratching my head over this one...

Forgot to mention that the bank 2 O2 sensor is working properly...
How did you verify your grounds?

resistance value of harness? what........I single strand of wire will show GOOD, but will NOT carry current and will become a voltage drop.....

You have to perform voltage drop tests ON ENERGIZED LOADED circuits.

search on how to do it. and learns it.

I will give you two quick possible reasons for 0 volts on the 02, that works

1) open
2)short to ground

both may NOT show up on a resistance test, with a common OHM meter.
 

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Discussion Starter #5
How did you verify your grounds?

resistance value of harness? what........I single strand of wire will show GOOD, but will NOT carry current and will become a voltage drop.....

You have to perform voltage drop tests ON ENERGIZED LOADED circuits.

search on how to do it. and learns it.

I will give you two quick possible reasons for 0 volts on the 02, that works

1) open
2)short to ground

both may NOT show up on a resistance test, with a common OHM meter.
Updated below and good points....


  • I'm not sure how the shop was able to get a voltage on 1 bank, as I'm seeing 0.0 volts at pins 29 and 43 with the car idling.
  • Measured 1.5 ohms resistance from the driver's side HEGO harness to pin 43 - HEGO unplugged
  • Measured 1.6 ohms resistance from the passenger's side HEGO harness to pin 29 - HEGO unplugged
  • Measured 12 volts to both HEGO sensors with them unplugged (i.e. orange wires) and the ignition on
  • Measured 3.0 ohms resistance from chassis ground near ECU to pin 49
  • Less than 2.0 ohms resistance from chassis ground near ECU to pins: 16, 20, 40, and 60
From the above points, I'm not seeing an open circuit. I do need to see if I'm shorting to ground. This was an issue I had with a 442 I restored and kept me busy for some time. I'll check to see if I have voltage to any of those grounds with the vehicle running. Any other ideas or suggestions?
 

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I am ignoring all your resistance checks, as I told you they are not valid........

do voltage drop test on, energized circuits.
 

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Did the OP ever find his problem? I am having the same issue on a 95 GT. No voltage to bank 1 O2 sensor. I am using the Moates Quarterhorse, and I will have very little voltage on cold start up and then it will drop to zero after very little time. I have verified that my computer is good on my brother's car. I have changed the O2 sensor harness as well. Been chasing this problem for some time now. Luckily this is not my daily.
 

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what was the results of your testing?

voltage readings.
 

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this is very common on the eec-iv's usually its the capacitors in the ecu have gone bad
 

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known good ecm was used apparently, no change
 
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