Hey all; I have a 1997 STS.

New Platnum +4 plugs, new FPR, new 02 sensor.

Always 91oct. Fresh fuel filter too. What on earth would cause 9.8MPG??

No hesitation at all..runs smooth. no overheating or anything.

 

running in low gear.
pull codes

.

 

perhaps a heavy foot and going up hill!

 

If you are going up hill and the incline is steep. I could see that kind of m.p.g. when you recorded that info. were you on flat ground?

 

parking brake on?

running on ethanol ?

timing off, wayyyyyy offfff......

 

Flat ground, no heavy foot. Driving normal! Always running 91oct. Tires might be 1-2psi under inflated, but I coudltn see that giving me the same milage as a 3 tonne 7L Hummer? Any sensors I should look at? I dont think this is a simple "change your air filter" or "Dont goose 'er " kinda thing here.

No codes are up, I pulled them the other day, then cleared them all, so far nothing new.