[vacationtime247]

Trying to find the best time to shift using the vacuum gauge. '91 Escort Wagon LX. 1.9 liter / automatic. Has 3 shift selectors on the shifter 1st, drive and OD. Typically drive 40-45 mph on the country roads traveling to work, @ the posted speed limit or lower. Quite a few stops, hills mixed with flat land. Last fill up I used the OD selected for the trans and at these speeds (40-45 mph) it would go into 4th / lockup. The vacuum gauge read in the drive range but low at 10-12 inches. This tank I've tried using 3rd gear at 40-45mph and the vacuum is reading much higher. Does this mean the engine is under to much load at these speeds using 4th gear with lockup? Should I always try and keep the vacuum gauge reading at it's highest point or go ahead and let it upshift? Should I keep it locked in 3rd gear since the vacuum gauge reads higher? Confused, explain.
VT247