Gas mileage keeps going down.

just a stab but maybe the o2 sensors are going south, also its a 97 so its 11 years old, maybe the catalyst is plugging up? Tires inflated to 35 psi? (or what ever the door asks for on the tire info placard) using E85 fuel? I understand many see a drop when they switch to e85 over regular petrol.

could be other things, could be a lot of things.

Don't use E85 but there is ethenol in the fuel. Tires have more than half life left and are inflated. Don't know where to look for O2 sensors or catalyst. lou

You *really* expect us to believe that?

The 'new' blends of piss and gasoline will reduce your mileage some as well. I think you are underestimating the loss due to the topper but I could be wrong on that since I can't see it.

Does it seem to perform properly still? I could see a failure to lock the TCC as a possible issue, draging brakes, or other similar thing, but I suspect your fuel is the main issue. The mandated blending of ethonal hurts mileage (you burn the same amount of gasoline per mile, however, so it doesn't (IMHO) help any on pollution).

Personally I would suspect you'd see a code of the O2 sensor(s) were off, but that could be the problem. The O2 sensors are in the exhaust system, one in front and one behind the cat typically--not sure about your truck, it may have four with two cats.

I had an older Dakota that dropped milage like that without throwing codes. Someone suggested the O2 Sensor, which I changed out, and I got my milage back.

FMB (North Mexico)

Yes, it still performs properly. No dragging brakes or inlaws. It's not empty but maybe 50lbs in the back. What is a TCC? And can the O2 sensors be changed in my driveway or do I need to take it in? Lou

exactly the upstream o2 sensor (the one(s) closest to the engine) has everything to do with fuel management. It is what tells the computer "too much" or "too little" in regard to what amount of fuel its putting in the engine while its running.

The sensor reading could be off and the computer would have no way to tell. the only thing the computer can tell about the o2 sensor is whether or not it is switching (rich/lean) as it should. and that is what the computer watches for in order to set or throw a code.

the catalyst is a "muffler like" device in the exhaust pipe. what i mean by that is the shape is similar to a muffler. you will find it between the muffler and the engine. This is not a part that most could replace on their own as the removal usually involves the use of a torch.

the TCC is the Torque Converter Clutch in the transmission.

the o2 sensor can be changed in the driveway, takes a 7/8" wrench, some penetrating oil and a lot of patience. they do make special sockets to remove them but i've found that if i can get a good 6 point combination wrench on the thing i've had better luck getting them out.

Ok guys I've had a chance to crawl under there and find the O2 sensors. While under there I see that the entire muffler is split. Its not noisy but I might as well change it. I can't remember the last time I had the catalyst changed if ever so I might as well replace that with the O2 sensors on both sides. Thanks for all the advice. Lou

if your muffler is split and your considering replacing the cat and o2 sensors its well worth it to take the thing to a muffler shop and have them do the sensors and the cat/muffler.

Oh I agree Chris, my days of tearing this stuff apart are way over. I'll be taking it into the shop next week for the whole thing. Lou