i removed the doghouse so I could have a pre-look at how bad the spark plug job would be... and noticed the vacuum hose completely disconnected from the fuel pressure regulator. Lots of dirty buildup on everything, so it's definitely been that way for a while. I cleaned it up and reattached it.

I look forward to seeing if it runs better than it has recently.

I will report back soon.

 

Interesting...I wonder what your fuel trims look like. That would give it higher than normal fuel pressures at low engine loads, which your PCM should adjust to with feedback from the oxygen sensors. Kind of surprised it didn't set a rich code.

 

i don't have catalytic converters, so that confuses it further.

Im under the assumption that the computer would have to adjust fuel injector pulse width to compensate.

Strangely, I've driven it almost 100miles since reconnecting it, and there is no discernible difference. Light throttle, heavy throttle: nothing.

I am watching the fuel economy though.

 

Not so much, when present the downstream O2 sensor is never used to adjust fuel mixture. The upstream sensors are used to adjust mixture once the PCM reaches closed loop status, which would compensate for abnormal fuel pressures. There are short-term and long-term fuel trims that are applied to the fuel tables to continually adjust mixture. My guess is that your fuel trims were in the negatives...beyond a certain threshold it would set a code for "Bank 1/Bank 2 rich".

 

Maybe you have a weakened fuel pump that won't get into the high pressure range but good enough to keep the injectors running. You also may have a bad regulator. A gauge on the fuel line and see what the readings are with the hose on/off to compare them.