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Discussion Starter #1
Little history.... The van had a serious thump when driving from a stand still... usually at a red light. Also, when cruising around a corner, hitting the gas almost always caused a thump.

Shifting from forward/reverse also causes thumps.

I had attributed this to multiple broken motor mounts...and was about to replace these.

Before doing this I decided to replace the O2 sensor on the cat...I was showing a ODBII code... no point in replacing the mounts if I fail inspection!

After replacing the O2 sensor... the thump is gone?!!! The van now shifts nicely! I still feel a thump going from Forward/reverse...this is due to the mounts.... But the annoying thump while driving is gone.

I guess the control loop that uses the O2 sensor was completely out of wack...and was giving the engine way too much fuel when accelerating?

For those of you experiencing this... think about your O2 sensor!
 

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Discussion Starter #3
I had/have the following codes:

P0730 - Low Tranny fluid
P0780 - Low Tranny fluid
P0420 - Failed Cat
P???? - Something about shift points


I replaced the O2 with a Bosch direct replacement...I think PN


The shifting improved after the O2 sensor. 2 days later I ended up topping off the tranny.

I suspect that they might all clear !
 

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Discussion Starter #5
The sensor provides fuel/oxygen information back to the computer... which in turn decides how much fuel to dump into the intake.

If the sensor says that the mixture is too lean when it actually is not...the computer may over compensate. This creates too much torque at shifting points.

All that I can say is that replacing the O2 sensor made a huge improvement.
 

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The sensor which provides that information is the front sensor which is right on the exhaust manifold. The one in the rear after catalytic converter is there solely to monitor the efficiency of the converter. It does NOT affect the mixture ratio.

- Vikas
 

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Discussion Starter #7
Well then I guess I must have a 'special' engine.... I'll I can say is that it changed the torque applied when shifting which must translate into less fuel.

You can't assume that the control loop does not include post cat converter information.

Either way, it helped my van ...all for $100 and 10 minutes.
 
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