I was getting around 21 MPG, and the last couple tanks have dropped to about 16.7 MPG while driving the same roads/highways. I am changing the airfilter today. Anybody know of anything else I can check out/replace?

 

plugs, wires, pcv valve, o2 sensor, fuel filter, pull codes

 

Any change in your heater/AC control settings lately? I was shocked to find out that setting the control to any of the dual-outlet pictogram positions also runs the AC pump (this is on an '03 2.3l B2300). The reasoning I'm told is the pumps last longer if there's oil circuilating. - Michael

 

Well I'm having the same problem too, so it will be of some interest, to see what you find & what the cure is.

I was thinking maybe dirty MAF, or perhaps you folks got a load of that high sulphur fuel that Motiva let loose over in Fla. Ruined many fuel tank guages & who knows what else before they got a handel on it.

There is a class action law suit against Shell/Texaco = Motiva joint venture in Fla.

Lady in Potland Oregon on another site, wth a 03 Toyota Corolla just made a trip down to Calif. & on the way back got a check engine light, finally traced it to a lazy O2 sensor.

We recently found out the nothern Calif area, up to Portland has also recently gotten a slug of high sulphur fuel, so we now suspect she took on a load of it during her trip & damaged her O2 sensor. Don't know how she could prove it though.

So if you've used any Shell or Texaco from Fla. or suspect you've perhaps gotten some in your area, as you're close by & may have been served by the same refinery, then I might suspect a lazy O2 sensor, as has been suggested.

A computer scan would be in order here, as has been suggested & IMHO would be a good idea, as it could, if your lucky, help you zero in on the suspect part, or at least the system, before you begin throwing parts at the problem in the hope of fixing it.

Don't know how many miles are on your ride, but if it's time for a routine maint. schedule & if you have not done it yet, I'd begin with that, along with the computer scan & see how things go, before a wholesale change out of parts.

It's likely to be somehing straightfoward & fairly simple.

I suspect my problem may be combustion chamber deposits, with a resulting retarded timing by the computer to prevent ping.

I suspect this as I'm beginning to hear marble noise again, on cold start up & for me that's a shure sign of deposits in my 99 4.0L pushrod engine, which has always been extreemly sensitive to the slightest combustion chamber deposit buildup.

It's also time for me to switch fuel brands, as I do this at every oil change to cut down on combustion chamber deposits.
It takes about 5 tanks or 1000 miles of driving for one fuel's detergents to clean the others deposits.

In my area & for my engine, I've found Chevron & Texaco fuels work best for me, so I switch between them, at every oil change.

So if you suspect engine combustion chamber deposits are causing your computer to retard the timing to prevent knock & thus affect engine efficiency, try switching between your two best performing gasolines at each oil change.

You may be plesantly surprised by the response you get, I was, on the Ranger & especially my 94 3.8L Taurus, Texaco REALLY woke it up.

 

My truck has just over 50,000 miles on it. I have changed many things and have done all the maitainance work on it. Really the only things I havnt changed that might need to be in the near future are the plug wires and O2 sensors. Last night I changed the air filter and fuel filter. The air filter only had about 10,000 miles on it and the fuel filter had maybe 20,000. I will be going on a 300+ mile trip today so I will know if changing those two helped at all.

The whole shell/texaco sulfur fiasco happenned in new orleans, about 70 miles from here, and I havnt heard of anyone having problems here. Plus, i only use chevron fuel. That is an interesting idea about switching b/w the 2 fuels. I might want to give that a try.

 

The AC compressor runs in the other heater/AC setting to remove moisture from the air.

 

Did you change the tires? That could make the speedo read wrong and seem like a drop in mileage. What else if anything has changed since you noticed the drop? Things to check:
1. Dirty air filter
2. Emission system problem (any codes?)
3. Low tire pressure
4. Brakes hanging up or wheel bearings too tight. Feel the wheels after you drive it for heat. Should be warm but not hot.