'97 4.6L Thunderbird POOR MILEAGE

[tapout]

Hello everyone.. I'm hoping you can help me determine what may be causing the poor mileage i am experiencing lately from my '97 4.6L bird.. I have replaced fuel filter, air filter, pcv valve, spark plugs, and spark plug wires. City driving is giving me around 14mpg Expwy driving around 21 mpg.. any ideas?? all bone stock..

Thanks in advance..

[zpn_by]

A few questions: what was the mileage before it went downhill? I've got an 07 mustang 4.6 that gives about 17/25 but it's shaped like a brick and up about 100hp on your 4.6. I'm guessing about 19/28 is what you should be getting.

Is your check engine light on? Even if not, try to get the codes read - there may be a code stored even if the light isn't on. (or, worst case - a previous owner might have removed the bulb! It happened to me) If you do get codes, post them here and that can help with the troubleshooting.

Are you the only person driving the car? If not, is the other driver's style and/or type of drive similar to yours?

Could someone be siphoning your tank little by little? We've seen it in our neighbourhood, but that was last year at 4.00/gal (1.50/L)

Last, How many miles are on your car? Is your transmission slipping? Are you using your a/c all the time? Did you just get the car during the winter?

As you can see Tapout, there are a lot of things to consider. It could be anything from emissions system components to driving styles or environmental conditions. We'll try to help you as much as possible, but the best thing is to try and get your codes read. If you do get any, please post the exact code, not what it means.

[BroncoJoe19]

I agree with zpn_by and ask some of the same questions.
What kind of mileage did you get in the past, so that we know what you are expecting?

I get 19 mixed, and 25 highway with my crown vic 4.6. I am gentle on the throttle. I imagine that if I drove it like I stole it, and could get the city mileage down to 12-14 mpg. Also city driving is a very relative term. Some cities have a traffic light every half mile, and can be driven through in 10 minutes, other cities may have a traffic light on every corner take ten minutes to drive 3 blocks.

[TBIRD430]

If your not driving this Bird like a race car driver, I would recommend you try cleaning the mass air flow sensor with some CRC brand (spray can) eletronics cleaner. Have the trans fluid flushed, the rear diff fluid changed out, and replace the O2 sensors with new Motorcraft parts (if these items have never been serviced before).

What type oil filter & oil do you run? Have you ever had the fuel delivery system serviced? If not, try searching "Sea Foam" on this site (& do the 2 can service).

Drive the Bird a few hundred miles and then get back to us...

[tapout]

thanks for the suggestions guys.. sorry i havent responded.. i was expecting an email to notify me of any responses to my post. Actually, this car is driven by my 76 yr old mother to church and grocery store.. believe it or not.. and sees an occasional trip out of town. She drives the speed limit.. never abuses the car and maintains it very well. She doesnt do any jack rabbit starts and the mileage has steadily gotten worse since we bought the car off a dealer a few years ago. I havent thought to have the codes read since there is no check engine light but that is a good suggestion... The transmission pulls hard and doesnt seem to slip.. so i guess i will start with the cleaning of the maf sensor and replacing 02 sensors.. the tranny and diff fluids will be changed this coming week.. I will keep you posted.. thanks for the responses!

[TBIRD430]

With this added infor, I bet a 2 can Seafoam brand fuel treatment will blow a lot of built up carbon out of the engine. Use the "search" function on this site & you can find out how it works. I would do this before the new O2 sensors too.

Good luck.