Sudden MPG drop

[RocketOgre]

I've had an SR in my hatch for almost 7 years now, I did the GT2871R .64 thing almost 5 years ago telling myself I'd go GT30 soon after so I have 755injectors and a Z32MAF tuned with a JWT ECU in retrospect I should have gone 555s but that's another story. Since the turbo upgrade the car has stayed in the 20-25mpg range like clock work. It's daily driven and it's been a habit of mine to calculate fuel mileage, check the oil and fluids etc. at every fuel stop since I was a young boy learning how to take care of my dad's pride and joy 65 mustang. Suddenly in December the fuel mileage dropped by nearly 5mpg on average. I see 16-19 now. I usually see my fuel mileage increase a touch in the winter since the whether helps me keep my foot out of it. I've checked for fuel leaks and vacuum leaks, hell any leak and nothing to be found. Idles fine, drives fine, pulls hard, warms up just fine I can't think of a damn thing. I'm assembling parts for the old summer tune up on it so fuel filter and plugs and all that will be replace soon, but on year old equiptment I can't for the life of me think of something that could account for such a sudden and then sustained drop. Any ideas?

[compactfean]

Check tps voltage, adjust, and adjust timing. Check to see if cts and oxygen sensor are good. And check base fuel pressure. That's pretty much everything that can affect fuel mileage. Oh and a clogged exhaust. Sounds like its time to check the electrical vitals.