Milage Is Down

[98BLACKBURB]

I have a 1998 Chevy Suburban 1500K ,350 (5.7),4L60E,3.42 Gears,all stock except RV Shiftkit,Flowmaster SUV Series,Foam Air Filter............My Question is I was getting 14.80 MPG.now it has dropped to 12.77...... ...Burb has 168,000 Miles...still runs good but looking for more milage,I've heard ethlynal cuts milage............Any Ideas.. ..thanks guys

Here's a pic of my 1969 Camaro SS playtoy Click once ,after it loads then click again....

[hubbycap]

My last tankful dropped about 2.5 mpg. from a consistent 16.8-17.1. WTF.

[Bish]

First thing I would think would be o2 sensors assuming you have done the standard tuneup items like plugs and possibly wires. No codes I assume? I replaced them on my old Tahoe at about 90K after noticing a drop in mileage. Immediately got the mileage back and I had no codes. I think they can get lazy. Does the 350 have a cap and rotor? If so, I suggest replacing.

 

If you replace the 02 sosnors, only replace the upstream ones (closest to engine) as the rears only tell if the cat is working or not and they do not affect mileage.

[JimL]

whats the temp guage at, if the tstat is stuck open it will run cool... Then it will run rich and your mileage goes to sheit...