I keep reading posts referring to gas mileage in the 25-27 mpg range. I have had 4 Reattas (3 '90s and 1 '91). and logged close to 500,000 miles in them combined. The '90s all got around 21 mpg on the highway, and the '91 will get about 24 mpg. I check the mileage every fill-up (because I have found the fuel guages to be unreliable) and the mileage rarely varies. Am I doing something wrong? I keep the tire pressures correct (to a little high), replace filters regularly, replaced the plugs with 100,000 mile iridium plugs, and I am not a hot-rodder. What else controls the mileage that might be causing to be so much poorer than the other posts I read?

I had a similar problem with my 90, only got like 26 on the highway if I remeber correct, and like 16 in town, will see what I get coming back from georgia, hopefully the trans rebuid will help a little

I am strictly an in town driver. Temps in OK are in the mid 90's. I drive with the AC blasting away. My '91 gets about 13-14 MPG. My '89 gets 12-13 MPG. Did a little better before the ethanol mix came on the scene. Definitely not in town cars but I love to drive 'em..

Mike

The oxygen sensor adjusts the fuel mixture. It is cheap so replace it.
Also clean the MAF and throttle body.
Contrary to popular belief a dirty air filter does not hurt Mpgs all that much but replace it. Use RedLine fuel System Cleaner or Techron.

Do not drive with lights on during the day time.
505 miles was my best tank in the 89 Reatta.

I've got an '88 and can register 35 mpg on the instantaneous readout but my overall mpg is in the 27 range at best. I drive by the instantaneous readout and starting out from a stop sign or light, I'm registering in the 7 mpg gallon range until it gets going. Also, I have one strange aspect to this car that I've never experienced with any other vehicle. It will idle at 1350 rpms and the car will do 40 mph until a an uphill changes the rpms and the mpg.
The fill-ups that I do rarely coincide with the car's computer. I put one gallon more in this last time than the computer said it used. I know that time of day and heat affect the amount of fuel that the tank will accept but...
The statement about the air filter's condition is also accurate. I could not loosen the screws holding the air box together and the filter had a little over 10,000 miles on it after five years of driving. The mileage did not change.
I also use Lucas products in the gasoline and oil, have a fresh tune-up and run the tire pressure a bit higher as well.
I really like driving the car but keep it as a back-up in case one of the work cars needs repair.

The fuel Economy calculator I believe is a function of the BCM and I assume must have factors built in to do calculations off either vaccuum or fuel injector pulse numbers.
Since going to the S/C the calculator is constistly off by about 10%. I don't think it even uses the fuel tank gage as a factor because the estimated range is now really far off.
The high idle you're seeing is programmed in, once the BCM sees a certain speed I think it's using either the cruise control or the IAC to elevate the idle. From what I've encountered in re-programming where the manual transmission is concerned, that elevated idle is to reduce emmissions.

I would pull out the IAC and clean it.

I've had 6 Reattas.
An 89 coupe got 30+ on the hy, my 90 ragtop gets better, the 91 seldon saw over 21.

Curious. Does anyone know how the trip monitor measures fuel flow? How do it know?

the 91 has larger diameter wheels , but they also bumped the axle to 3.3 or so
wife's lesabre at 70mph is short of 2000 rpm and gets high 20 / low 30 on the highway.
91 is 2000 or so at 60mph , haven't had it on a super slab for any length of time as yet.
91 has too many rpms for cruising and in town , although it is a bit quicker.
for pre 91 try 16 inch wheels probably need a prom change to keep everything even up. but will result in lower cruise rpm on hwy. pre 91 has enough torque that it shouldn't matter power wise.

There were some problems with the fuel calculations in the computer. See previous posts. If you are going by your computer's estimates they can be way off. My 88 says I am averaging 18 mpg, but I have never had less than 25 mpg when I do the math myself. There are some previous posts about a chip to rectify the problem. I just do the math.

With the ANCX Prom my 88 is pretty close on trips, not so in town - only once or twice have I put in as much as the computer said I used. Idling seems to be the worst.

Also the 225x60x16s read about 2 mph low - is 57 mph when it reads 55, suspect a 215x60x16 would be just about the same as stock 215x65x15s.

I am not seeing much difference with what may be ethanol enhanced(smells sweet). BLM is sitting in the 135-138 range. MPG may be down a bit. Of course in this weather the a/c is being used more and that has about a 1 mpg impact (see http://www.nrel.gov/docs/fy00osti/28960.pdf for a report and some interesting thoughts (Floridians always seek shade))

So is it generally agreed as EDBSO suggested, that assuming the car is in a good state of tune, mileage is mostly controlled by the O2 sensor? I drive carefully, but above 70 on the freeway when possible. In 50/50 city/highway driving I get right about 20 MPG on my 90 [70k] correcting for the larger tires. That seems a couple of mpg low given what I am reading and that we are not talking large elevation gains/losses.

I just topped off my 91 this morning, gas here (89 octane) was down to $3.86. I put in 4.5 gallons (per the pump) to get it back to full and my trip odometer was at 75.5 miles since last refuel reset. This comes out to about 16.8 MPGs, in combined city/highway, mostly city, A/C running most of the time with outside temp in the mid 90's. Any yes, I am a bit heavy on the pedal, but I do not gun it off the line at every stop sign and green light.

So, my mileage is not great, about 2-3 MPG better than my 95 Deville gets in the same kind of driving. Of course, the Cadillac takes premium, has 8 cylinders vs. 6 and is about 1200 pounds heavier so I would have expected a bigger difference.

Note that I need to do a tuneup, I have been putting it off because I have too many other tings going on right now and it is too hot to work on the car during the day. Maybe this will make a notable difference.

KDirk

I strongly recommend that you open an account here and log every tank.

YAHOO I am over 9% over the EPA estimates!!

Well, based on what EDBSO wrote, I decided to install my spare O2 sensor. Turns out the old one was not very tight, but worse, it was either separated at the base or very nearly so. Doubtful that it was doing much sensing. Now that I have the new one on, we'll see what a difference a day makes.

It likely would have read lots of extra oxygen and made the mixture richer which tanked your mpgs.

Good luck and start logging.

Does the O2 sensor have a default mode? I am thinking it was not operational at all. Just the process of carefully putting a box end wrench on it made the top separate from the base completely. I could then put a deep socket on the base and it wasn't very tight.