It's hard to believe myself - - -
3 weeks ago, Ron and I regrooved my TB and I reset the fuel trims. Took it for a road test and noticed on the scan tool it was staying in "open loop" all the time. This means it was running rich, as if it was just started and engine was cold. Bad for MPG. My pre-cat O2 sensor was very sluggish - original sensor with 220k miles. Well, being the cheapy I am, I put off replacing it. Up to today, mpg has been around 19. Normal is around 22 - 23.
Today I broke down and replaced the O2 sensor. Drove the van to work and scanned for "open/closed loop" status. Still Open after driving 30 minutes.
Replaced the sensor and reset fuel trims. O2 sensor now responding properly between .9 mv to .1 mv. Fuel trims were adjusting down from a "high" of 20% positive.
Now for the really good news.........
Drove home. 15 miles into trip, checked fuel trims, load%, O2 output, and on-board mileage computer which does avg and instant mpg..........
Short term fuel trim - fluctuatin around -9%
Long term fuel trim - stable at around -19% - - - not a typo
Load % at 55mph, level road - 50%
O2 reading - flux between .9 and .1
And, get this, On-board mpg showing 28.6 mpg AVG., and of course instant flux based on throttle response.
That's a 50% increase from the morning trip, 30% increase from normal!
I have not checked the tailpipe yet for smell. I want to let the system clean itself out. We are taking this on a trip down state on Thursday on the interstate. I will monitor the mileage closely.
I was going to regroove this, but I don't think so now.
Scott Castleberg
Pellston, MI
Gadgetman Michigan
