in my 87 bird, i got in and started driving the other day and i had a bad miss when i try to accelerate. I just replaced both the plugs and the wires. Along with the miss my gas mileage has decreased greatly. Could it be something with the FI?

 

Did you replace the distributor cap and rotor when you did the plugs and wires?
Did you have the same miss prior to you replacing the plugs and wires?
I don't think that you will be getting that kind of a miss if you have a problem with the FI. However, you might have also a bad O2 sensor, and that, along with an ignition problem will give you poor fuel economy.
Make sure that you have a new rotor and cap.
Make sure your plug wires are installed all the way and correctly, and that they are not touching the exhaust manifolds.
Does our car's SES light come on?
More info is needed.
You could also be getting a similar symptom if you have an intake vacuum leak. But I would check the other things first

 

Saculia, thanks for your reply. No i didn't have this miss prior to me changing plugs/wires. My SES light does come on after driving for w while I have not replaced the distributor cap, rotor or O2 Sensor. I may have to give that a try.

 

double and triple check to make sure you put the correct wires to the correct plugs. Remember on these V6's, its 123456 which isn't even remotely close to the SBC 18436572 (obviously minus 2 cylinders)

 

Check your wires first. Make sure they are ALL THE WAY on the plugs and the dizzy cap.
Second, if you did not buy AC/Delco R42TS plugs, go out and get some. Anything else just sucks. Believe me, I have used Bosch +2's, Autolites, and I have even had Champion plugs in my engines. AC/Delco plugs are what these cars like best.
And, do a search for the TomP tuneup. It might cost you a little more, but you will be saving yourself a major headache and your car will perform better in the long run, making you a happy camper.

 

I second that, make sure you are running AC Delco plugs. Re-check your firing order.

Whenever you have an "all-of-the-sudden, brand-new" problem, always go back to the last minute that everything was just fine. Then slowly draw out a time line of what happenned after that.

Everything was fine, plugs and wires were changed, now there's a misfire...

Maybe one of your plug wires came apart or one of your new plugs is broken...