Vacuum Gauge & Automatic Trans Shift X's
 

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

when selecting the gear, the lowest rpm possible will be the best choice, as long as you are not at WOT.

The vacuum gauge is not going to help you select the gear,
but rather, let you select the vehicle speed for the given gear that obtains the highest vacuum in that gear .

Neutral coast downhill with the engine idling, if the grades will allow you to do so.

Highest gear possible for best mileage.

Try inflating the tires to sidewall max.

Coast in neutral with engine running (idle) as much as possible to forced stops.

Vacuum reading in highest gear at 11-12 inches sounds a little low to me but it changes drastically depending on the grades involved.

Make sure the alignemnt is good and no brakes are dragging. Does the car push easy on flat ground?

regards
Mech

Been neutral coasting using both EOC, engine on and off. Will inflate tires up to 40 psi soon, should have already. Last tank was one of the best I've had. Getting better, but need some more practice. Car doesn't pull or seem to have any alignment issues after ball joint and tie rod end replacement. Was on the fence about if it was better to use 3rd gear or 4th at 40-45 mph. Thought perhaps the engine was under to much load in 4th making the vacuum lower. Brakes don't seem to be dragging as it's easy to push by hand out of gear in neutral. Last tank was 34 mpg, don't see any reason why I can't get it up to 40 mpg with practice. Hopefully I won't be driving it much soon as the weather is warming up and the motorcycle will take it's place as my daily driver.
VT247

engine vacuum readings only tell part of the story. lower engine vacuum can be a more economical choice.

the increase in engine rpm requires more power just to turn the motor.

and higher rpm means more injector firing events just to maintain the same air/fuel ratio, even though they are smaller amounts due to the higher engine vacuum.

With the O/D transmission in your Escort 40 MPG is achievable, but you'll probably have to work at it. My dad had a '94 Escort LX sedan with the O/D transmission and I think he was able to break the 40 MPG barrier a few times in it. I noticed your 90 day average is below 30 MPG, 35 should be pretty easily obtained with this car by simply adjusting your driving habits if it's tuned properly. I've got 4 Escorts with the worst one on gas being an '88 GL with a 1.9L 3 speed automatic and I can usually get somewhere between 30-33 MPG in mixed city/highway driving as long as I keep the speed at 55 or below on the highway. Your O/D should be worth a few extra MPG since you are probably lowering your engine speed by 600-800 RPM in overdrive. I'm not sure about yours, but I've found 50-55 MPH seems to get me about the best mileage in the automatic since it doesn't have to down shift to climb fair sized hills.

Keeping it in third gear didn't net me anymore MPG, actually lost a few > : ( Last tank using the overdrive was much better. Have since filled up and I'm hoping that I'll get to see 37-38 mpg this tank. Rarely have any other cars around on my way to work. Been doing a lot of neutral coasting with both engine on and off. Wishing it was a 5 speed.
VT247