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Sensor's and MPG
03-27-2012, 02:06 PM
Post: #1
Sensor's and MPG
Hello To All -

1990 Cadilllac Deville 4.5 L FWD 182, 000 mi.

Recent Tune-Up / No Error Codes presently.
I am curious if it would be worthwhile for the purpose of increasing
gas mileage to perform an extra careful voltage measurement, etc.
test of each of the Emission Engine SENSORS ?
Would weeding out old or on the border of spec's SENSOR's
help a vehicle's gas mileage ?

Thanks for any input.
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03-27-2012, 11:31 PM
Post: #2
RE: Sensor's and MPG
Probably not, although if you just want to putter with it may be interesting enough just for the learning experience.

Here's what you have to work with... and it's not much. The car is OBD-I so rather primitive compared to later versions of the same vehicle. In your case the ECM does basic monitoring and fuel trim using input from temp (air and engine) plus throttle position, manifold vac, engine speed, and exhaust (O2) sensors. There is no monitoring of the cat efficency, and likely nothing watching the trany shifting either. The trany is just doing the gears based on road speed and engine load.

About all you can see with a fancy scanner might be the input readings, and they will all be within "normal" range unless the dash light is on.

Now, if you were just trying to improve MPG, what I would do is jack the tire pressure to the max (on the side wall of the tires) make sure the front end is properly aligned, (less rolling friction) and drive it easy. (light foot) Also brake easy to get more coasting. If it's due for plugs and other tune items you should consider that too. Typical results with these tips (all combined) can add 10 - 20% to your MPG. Sometimes just changing the way you drive (or where you drive) can do the same.

BTW, my father had a 92 Caddy and he got 5 mpg more than my mother did on the same car. Amazing what switching a driver can do, eh?
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