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Discussion Starter #1
I am having an issue with my 5m-gte in my pickup. For some reason the ecu is not referencing the o2 sensor at cruising speeds as it should. I have replaced the o2 sensor with a few of my spare nd sensors and then I bought a bosch sensor and they all act the same way (except the bosch unit reacts and warms up quicker). The only time the ecu "looks" to the o2 sensor is while cruising around town below 35 or so. And then when I give just the slightest increase in throttle my a/f guage goes rich and stays there until I back off to almost closed throttle before it oscillates again. Could this be a faulty afm? or something else. This is becoming very frusterating.

Matt
 

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It sounds like it's dropping out of closed loop. I would check the TPS and it's adjustment.
Have you "adjusted" the AFM? If not, then check the resistance curve per the TSRM, but the AFM isn't the deciding factor in closed/open loop operation.
The TPS is what tells the ECU to ignore the O2 sensor when it reads WOT or 70% throttle, depending on which year setup you used.
Ihth,
Jamie
 

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Discussion Starter #3
Im pretty sure it is not the tps. Since I unplugged it and drove home and it did the same thing. The only thing that happened was the rpm's rose at idle. Could anything else cause the ecu to fall out of closed loop? i.e. water temp sensor, afm, rpm sensor etc. Noise on the sensor wires?

The system I am using is from an 83.

One more thing it seems totally dependant on throttle, with or without the tps plugged in.

thanks.
 

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i would imagine it would be in open loop mode without the TPS connected, so i wouldn't rule that out yet. it also stays in open loop mode when the engine (and o2 sensor) is cold, so if you have a bad coolant temp sensor, so maybe that could be it.

shiva
 
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