MPG - Dramatic improvement I don't understand
 

I have a 2002 SC430 with 115k miles and in great condition. All stock except for downsized wheels (16" on 55 tires).

When I bought the car this winter I put in around 33psi on the tires. Since then I've been getting around 19-20MPG on my daily commute.

A couple of weeks ago I did two things: I put 37psi (more for handling than mileage) and poured a can of injector cleaner into the gas tank.

Now I'm getting 26MPG on exactly the same driving conditions!!! I don't get it. I know from a scientific standpoint you shouldn't change two variables at the same time, so now I'm really curious to know if the change was the tire pressure or the cleaner....

What do you guys think? I have since lowered the tire pressure a bit (36 in the front, 34 in the back, car was too jittery) and I'm still seeing ~26MPG, so I'm inclined to think it was the cleaner... but it seems too much improvement to be just the cleaner.

thoughts?

cs

If your injectors are clogged, which is common, can make a dramatic difference. I remember about 10 years ago I used to drive a jag, and I always thought it was slow. Then I put a bottle of lucas injector cleaner. The car instantly turned into a monster. Night and day difference. Didn't keep track of mpg but clearly there was dramatic difference in fuel delivery. Have been using quality fuel injector fluid like lucas, seafoam, etc every since!

Plus I wonder if tire size could have effected your computers calculation of mpg??

A clogged injector can have huge effect on gas mileage, and in many cases, you can't really tell with modern engines if it's not pulsing properly because the electronics will compensate for it (retard ignition). You may also have noticed that the car is idling more smoothly.

It's always a good habit to throw a bottle of injector cleaner in the gas tank about every third fill-up or so...pays for itself in the long run.

Also

Winter weather mpg is typically 10-20 pct lower than warmer summer months.

Winter blend gas is also less efficient.

Thanks all. I hadn't thought about the winter blend... maybe that has something to do with it as well...

Only caveat is if you use to much maf sensor may be effected and spark plugs will get residual build up.

Just did a plug replacement, injector and throttle body clean, as well as partial new fluids (coolant, tranny, etc). Drove 85 miles at 75 miles per hour and recorded 27.5 MPG. I'm thinking the injector and throttle body clean are the biggest contributors.

Warmer weather and cleaning out your injectors is the cause of your increased mpg. Also changing spark plugs, cleaning the MAF, a k&n air filter and cleaning the throttle body will improve the efficiency of these motors.