I have a 93 sdv with 4.9, according to the fuel data im only gettin 8-9 miles per gallon. I think it might be right because i rest thtrip odometer and had five gallons in it and i was on empty at about 42 miles. I fix cars for a living and ive done a complete tune up on it including replacing the oxygen sensor, fuel filter and doing a fuel rail cleaning. the car has just a little over 100,000 on it. I dont know if it makes a difference or not but the fuel date module thats in it right now is out of my 86 sdv, im hoping im just getting the wrong info from the module. I really like this car but if i cant get better fuel mileage then its going up for sale, I figured ill ask some of you long time caddy owners for some new ideas.

As you probably know, the '86 is a HT4100 I believe but I thought all calculations where done by the PCM. If not, that may be your problem.

I assume you checked the FPR?

im sorry what do you mean by ht4100, and i am starting to lean towards the pcm

The HT4100 is the 4.1 engine Caddy used for most of the '80's.

I just replaced the plugs, cap & rotor on my '89 4.5 TBI with 100k and got 26 mpg on the highway afterwards. I get about 18 mpg around town if I soft peddle.
With PFI you should be get a couple mpg better than I. I would do some hard, real time calculations of miles/gal and see how it compares to your fuel data center. Hopefully it's just a matter of incompatibility between the '86 center and the 93 PCM.

Im going toworrow to try to find a fuel data module thats close to my 93 sdv. Thats a good point Kev thanks for the advice. Ill let you know what the outcome is.

Im going toworrow to try to find a fuel data module thats close to my 93 sdv. Thats a good point Kev thanks for the advice. Ill let you know what the outcome is.

Do not quickly dismiss Ranger's comment about the FPR.

There are two known fuel wasters for the 4.9L. The first being a leak from the fuel pressure regulator, and the other is a stuck or leaky injector(s). 8-9 MPG is very likely according to your post. Also likely not the result from the wrong fuel data module.

On any given bad day, you should average around 16 (15.7-16.2) MPG around town. If not, there is a problem.