Bad Gas Mileage, WHy?

[michaelmiller85]

I have an 89 FI Manual Festiva. The body is a 89 and the engine and tranny are from a 91. The computer is for an 89 Auto.

I do not have the correct computer for this car, and was wondering if this would cause me to get bad gas mileage?

I drove short 5minute runs and got 30mpg, and then went on the interstate and still got 30mpg. It doesn't seem right that both city and highway be the same, plus i thought these cars were supposed to get 48mpg. My b6t got 36mpg, shouldn't i get more?

Michael

[Levitan]

Things to check first: Complete tuneup incl air filter and pcv valve, tire pressure, and catalytic convertor.

[michaelmiller85]

I'm have never owned a 1.3L festiva, do they usually seem really weak? When on the Interstate, i had a hard time making it up hills without decelerating huge amounts. Is this normal?

Michael

[Levitan]

I'd start with the tuneup, but I have a feeling your cat is plugged. You have to have air leaving the motor as fast as going in the motor. When the catalytic convertor plugs up, prevents the exhaust from leaving the pipe. That means a car is spending energy pushing exhaust instead pushing car. DO you hear a "whooooooosh' exhaust sound(beneath or maybe from in front of the car, not the rear like normal) when you accelerate? That be the telltale sign of plugged cat. First and cheapest thing I would do is tuneup and filters. If the cat is plugged cut it out and it's up to you whether or not you put it back in. Legally, yes, but many ppl will argue many different points of view on reinstalling the cat.

[collegeboi]

i get about 30 i thionk, next week will do tune up and c as well.

[WmWatt]

You can detect a blocked exhaust with a vacuum guage. Look at the article on vacuum guage diagnostics at the top of the forum.

[Levitan]

You can detect a blocked exhaust with a vacuum guage. Look at the article on vacuum guage diagnostics at the top of the forum.

Absolutely correct!!! I didn't even think about that. Good call Wm!

[packrat427]

I am not sure how many different computers there are , but I am going to go with the problem being what you said in your 1st post ..
Not sure how well the auto comp works with the manual .
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I have an 89 FI Manual Festiva. The body is a 89 and the engine and tranny are from a 91. The computer is for an 89 Auto.

I do not have the correct computer for this car, and was wondering if this would cause me to get bad gas mileage?