Hey guys,
Just got a t-bird from my grandfather on the road, and have a couple questions. First off, the car has been sitting for about 2 years give or take a couple months. The whole break system was screwed so I replaced just about the entire set. It's been "road ready" as my dad would like to call it for about 3 days, but I'm wondering how bad old gas (had about a half a tank when it was parked) would be for the car while running it, even lightly.

I've been debating on flushing it, but I've never done it before and would like to know if just mixing it with new fuel would be okay for it. I've decided to run mid-grade in it and then moving up to premium, but the old gas might leave some residue is where my thought process is going.

In summary, my question is what would be the negative outcome of running 2 year old gas through the engine, and would mixing it with newer fuel (higher octane fuel?) be efficient in leaving a minimal amount of residue? Or should I just flush the whole system?

 

I would fill it up with mid-grade fuel and stay with mid-grade or regular. Maybe I would replace the fuel filter. I would only go further if problems develop.
You don't need to go to premium and pay that premium. It is about 10% more expensive and gives you: nothing. Higher octane only helps if the engine needs higher octane. Just stay with "tier 1" fuels. The big brands only sell "Tier 1" fuels.

A higher octane fuel is harder to ignite therefore it is used in high compression engines to combat ping.
Old fuel is harder to ignite because the most volatile parts have evaporated. Mixing it with fresh fuel helps.

But do something for the engine: you probably changed the oil already. Change it again after 600 miles or so, then go on a regular schedule. And do something for the transmission: have it serviced.

 

Hey, first off I'd like to say thanks for all of your input.

Turns out my father took the car out for a spin before I could got home from work. In his words, "It idled fine and drove great at first, but then after a while it started misfiring after about 50-75 miles". So now the check engine light is on (great considering I haven't had the time to get it inspected yet), and occasionally changes to flashing. My assumption is that it's due to the old gas since it wasn't apparent from the beginning.

The car is made to run on regular by the way, but what I'm thinking is that the bad gas might have messed up one of the coils or something, but I'm also not totally competent at guesstimating when it comes to cars (yet!). Tomorrow after work I'm going to go to the local pepboys or autozone and getting injector cleaner (when I take the car out I'm gonna use it when I fill the tank), and getting a OBDII diagnostic unit. That's the unit I've been planning on buying, just wasn't planning on it so soon.

Think I'm looking in the right direction with a coil?

 

I think it has a coil pack. I would take out the spark plugs, inspect the wires and inspect the towers of the coil pack. If there is any slight doubt about the plugs and wires I would change them. Same with the coil pack.
The blinking CEL is a warning that things are so much out of whack that it will damage the catalytic converter if you don't fix the situation.
I think there was crud in the tank and it plugged the fuel filter. There you go: clean out the tank and replace the fuel filter.