badazz769

Ok, so i have a 98 WS6 and I usually get gas at the same gas station and have the same driving routine thru the week and i get about 18-20mpg. Well my last 2 fill-ups have been at a diff gas station and ive noticed that my car has only been getting about 14.5-15mpg! So i filled up this last time w/ the gas i was using b4 i swithed to see what it would do and it still is getting bad mileage. So im wondering should i run another tank or so thru it w/ the gas i had been gettin and see if it changes? Also, if it does not change, what could it be? My car is not running any differently than ever b4 so thats why im confused. Should i maybe try some injector cleaner and see if its something simple like that? If anyone has a clue please let me know. thanks

wssix99

iTrader: (5)

This is most likely caused by the mechanical properties of $4-5 gas. It has probably happened before, but you are only noticing it now. (Dropping from 20mpg to 14.5 is not necessarily a problem, and shouln't cause any immediate alarm. Keep in mind that driving conditions can cause fluctuations of 18 mpg between city and highway driving.)

Regardless of your situation, you should be sure that you are using the correct high octane gas as described in the owners manual and a Top Tier gasoline as recommended by GM to keep the engine clean. If you do that and maybe do a periodic carbon cleaning, you should be in great shape.

My city driving mileage on my '99 WS6 fluctuates has fluctuated from 12-20 mpg in city driving, depending on the conditions and carbon state of my engine. The recent fluctuations you have seen can be explained alone by using the A/C more often in the summer heat, etc.

You should give it a few more tanks to see if you have a real trend or just a one-time blip. If you have not done a carbon cleaning, you may get some better mileage from doing one. (It won't "fix" your recent fluctuation, but could give you a general boost regardless.) You'll see many posts here relating to SeaFoam treatments to do this. I took mine in to a shop to get a MotorVac CarbonClean treatment done (Achieves a similar aim with less time/mess but more $$$.) and got an additional 2 mpg across the board city and highway.

Jon Boy

The mpg dropped bad on my Z71 last year . Right before, I had put fuel injector cleaner in it. Turns out, my fuel filter was clogged and caused my mpg to go down drastically. It might be worth a try.

Empatho

iTrader: (16)

+2 on the fuel filter
and also seafoam your car

badazz769

thanx guys, ill check it out.

LT1Formula26

ive heard bad stuff about sea foaming, any negatives? what would it cost to get a new fuel filter?

Blazingz28

iTrader: (5)

very very cheap and easy to do fuel filter. maybe 10$ ?

-jack up left rear
-open gas cap(not necessary but I have done every time)
-OPTIONAL:take a screwdriver and shop cloth and purge the shrader valve on the front of the driver fuel rail (bike tire type valve)
-A foot or two in front of the rear driver tire you will see a metal cylinder with a line running in and out, this is the filter.
-Disconnect the side with the nut, takes 2 wrenches
-push in the 2 clips and pull the filter off both sides
-let the fuel drain, or try and put the new filter on as quick as possible if you don't want to make a mess.

Done!

LT1Formula26

sweet, ill have to do that then, but not sure if fuel filter is the prob. i thought the new pump came with one.