Burning rich

[Raptor05121]

for the past month and a half I have been using the same BP gas station for gas (only one in town that doesnt have E10) and I've been getting 16mpg if i drive like an ass in town, 18 conservatively. Very recently I noticed shes burning fuel. I mean, 65 mph on the highway and I'm getting 13mpg, and only 9 mpg city.

I cleaned the MAF, IAT, IAC, filter, and throttle body with a PCM reset. Nothing. Returned my 87 street tune to stock. Nothing. Tire pressure is good, and I have a dual-core radiator, 180* thermo, and electric fans keeping my water temp at 180*. Oil changed with Motorcraft 5W-20 Synthetic blend 800 miles ago, and no CEL. Plugs are Motorcraft platniums gapped appropriately about 10,000 miles ago. Coil pack has never been changed and wires have never been changed. The fuel filter is over 8K miles old.

My truck has FOUR oxygen sensors and id like to know which is the problem one (if it is even a O2 problem) before i go spend some money.

[bk_cauley]

Im not sure if tony and D have a scanner or even if the tuning software reads stock o2's, if they can put it on the scanner and watch the 02's counts. they should all be within a certain percentage of each other. And another thing to think about is clogged catalytic convertors.

[Raptor05121]

Yes it may be a clogged cat. I did put some Gumout in my tank about a week ago. I just datalogged my O2 sensors and the front ones (from what I am told are the ones that control A/F) are swinging back and forth together, so Im guessing those are okay. My left rear isnt doing diddly squat though and my right rear is moving a little bit with different throttle pressure