I have a 94 formula which has not been running right. When you get to to about 1800 rpm's and keep pushing the pedal it just holds that speed for a while and then takes off. I unpluged one of my o2 sensors and how it runs fine. I am right that by unpluging the o2 I am forcing it to run in open loop? If that is true which sensors are not used in open loop? I have a laptop and the only code a get is for the o2 sensor that is unpluged. Please help me.
Thanks

 

o2's get lazy or slow to respond, How old are they? What does the laptop show for the signal change?

Bosch recommends testing by warning up the system including the o2s and disconnect the o2 your testing. Hook a meter to the o2 and disconnect a vacuum line. If the voltage drops to .2 volts in one second it's ok but if it drops slugishly or never gets to .2 then replace it. They also have a rich prodcedure but that requires propane.

Hope that helps Good luck to you.

 

The o2s are only 6-8 months old. I have not logged any runs so I am not sure how fast they are changing. Is there any sensors or anything that would not be use by the pcm when the o2 sensor is unpluged?
Thanks

 

Any one have any ideas? I do not think it is the O2s because it does it right away. Is the Maf use when the 02s are unplugged? Are there any other sensors that are not used when the O2s are unplugged?

Thanks

 

So your saying you can actually drive without them pluged in then and it drives fine, it go's back to its default setup i read somewhere too right?

 

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The only difference between open loop and closed loop as far as the sensor is that the PCM ignores the O2 readings. It still uses the MAF to measure air mass flow, the inlet temp sensor, coolant temp sensor, MAP sensor, etc. It just isn't trimming fuel based on O2 sensor feedback.

When you are in closed loop, the PCM looks up a long term fuel correction for each driving condition (CELL, a function of RPM and MAP), then uses those corrections to fuel the engine. In open loop, it uses CELL 17 and 18, which contain long term fuel corrections based on all the other cells... some sort of algorithm that calculates a value.

So.... it appears that the problems are in the long term fuel corrections in the 1,800rpm range and above. Use your laptop scanner to log a wide range of operating conditions, so you can see the long term fuel corrections for CELLs 01-18. That will help point you in the correct direction.