My '00 OBS 2.2 ran strong after an ECU reset, but after a certain number of miles would revert back into a (fault) mode where below 4250 the torque was diminished A WHOLE LOT (no displayed CEL however).

 

Remembering stories about the electrical ground that runs between the firewall and the trans being critical for eliminating "phantom" hesitation problems, I went ahead and ran a nice new fat ground between the firewall lug and the engine block. BAM! Problem gone.

 

My question is this: has anyone ever figured out the specific mechanism that's at play here? I hate "fixing" something without knowing what I actually did.

I would suspect that the ground eliminated noise from the ignition system getting into places it shouldn't normally, since the ignition pulses are so high.

And I guess I would think that it might be because you eliminated an intermittant connection. Ground is so critical on modern cars as excess wire size and grounding straps have been eliminated to save weight and money. Even the batteries are smaller in many cases. If you live in a salt state your car may need all the gound help it can get.