Diminishing MPG's
 

Hi guys,

another day another problem. been noticing im getting less and less miles out of my tank before the light comes on.

fill up 1 - 313 miles filled up 14.6 gal (when light comes on)
fill up 2 - 245 miles filled up 14.5 gal
Fill up 3 - 210 miles filled up 15 gal

driving style is consistent (pretty spirited), and i noticed my MPG fell after i changed the trans and diff fluid, which i cant imagine would affect the mpg that much, plus with the z-tube i should be able to pick up a mpg or 2...

car has new air filter, cleaned TB, fresh oil, new pcv valve, new trans fluid, diff fluid, z-tube

still on the list to change is spark plugs...

any advice is appreciated, would like to catch any potential problem is theres one

I would change out your plugs then report back. Also I would probably run BG's injector cleaner through the system and see what happens.

thanks, ill try it with the next fill-up.

Big6, the mileage we get depends on where we drive and under different conditions! Driving around town don't expect even good mileage, on roads where you can use your cruise control is where you'll do the best! I've never been a fan of driving until the light come on, anything below 1/2 tank I'm looking for a Chevron station. Having your G serviced won't effect your mileage in a negative way! About every second oil change I always drop in a bottle of Redline injector cleaner, AMSOIL also makes a great injector cleaner...either one will get the job done!
Gary

im mostly driving around town since i dont commute on it.. i used lucas cleaner before and dont think i've seen a difference..my top choice is shell super, then bp, then everything else.. my daily is a RX330 and ive seen a 4mpg + difference going from exxon to shell

Using Shell gasoline I consider myself lazy because they're a few blocks closer than my Chevron station and mileage isn't as good!
Gary

I'm not sure where you're getting the idea that a Z-tube would give you better mpg, but that's neither the problem or solution.

What it sounds like is that your O2 sensor is starting to fail.

Possibility, wouldn't he be getting the "Check Engine Soon" warning of the dash? :smile027: Something we all dislike seeing...Gary

That would come as soon as it fails completely. O2 sensors actually wear out progressively and one of the tell tale signs that it's on its way out is that your MPGs get cut by about half.

It's my experience people get varying results from different brands of gas. My G and my GTO for some reason prefer Valero over all others for mileage and performance and I've tried a lot of brands of gas over the years. Might be a regional thing. :dunno:

Valero is actually garbage. They use heavy sour crude vs shell or Chevron who use light sweet crude. Valero also JUST recently became top tier (strictly for marketing purposes) which means it uses outstanding detergents, but considering Valero is so small compared to other top tier companies, I'm almost certain that they use the bare minimum amount of detergents to have the "top tier" label. I worked there for 13yrs and the regional repair guy was an old timer car guy who had an srt-8 Challenger and he said he'd never put Valero gas in his car.

He also had a 2700lb 67 Dart swinger that ran 9.9 1/4 miles, so he new a thing or two. One of those older guys who keeps up on tech cuz he's been doing it that way all his life. I miss that guy. Haha

Tire pressure
Any junk in the trunk?
I'm sure if you fill your tank and drive 300 miles 65-70 MPH you will see much better results. I use WaWa gasoline and fill up before the light comes on usually at the 1/4 mark.

Telcoman

Is your car a 6MT or auto and what year is it? What oil are you using in the motor?

Check your brakes to make sure there's no dragging and that your parking brake is completely disengaging. You could also have worn wheel bearings adding drag to your rolling efficiency. The front wheel bearings aren't known to be terribly durable on these cars.

i'd think better airflow would help it run a litte more efficient but i get that its most likely not the solution or problem.. i am too starting to suspect the 02 sensors, gotta find my o2 sensor socket haha

i'd guess its regional, some poeple swear by valero and delta, the worst gas in my experience was costco, my RX and my gf's ecoboost mustang saw a crazy drop in mileage and the car felt dull and sluggish