Reattas, MPg, & Congress

[padgett]

In running the O2 sensor tests I noticed that peak mpg occurs between 45 (TCC lockup) and 60 Mph, decliming after that to about 24 at 70.

On reflection this indicates the regulations in place then - may not be evident today but all Reattas were designed and build during the dark period of the National 55 mph speed limit which was repealed in 1995. Consequently "speeds in excess" were not really considered.

Note that the SII 3800 cars were introduced after the repeal when speed limits were returning to pre-1973 levels. Today except for a few slowdowns around cities, my entire Olando-New Orleans trip was under 70 mph limits with most traffic running 5-10 mph higher.

Now while the "C" engine does very well at this, it was really optomised for 55 mph and it shows.

[Guest EDBSO]

Could this not also be a function of increased air resistance at higher speeds?

I have read that you can pedal a bicycle at 60mph if you remove all air resistance. Have actually seen test track films of bicycles drafting behind transport trucks doing 60 with the wind resistance broken.

Kinetic energy (moving energy) is expressed as 1/2 of the mass times the velocity squared. This is why going very fast takes a lot more power?

Just my 2cts, not a technical paper just some vague thoughts.

[Guest Buick Mike]

Believe it or not, someone has pedalled a bicycle 152 MPH (no typo, that's 152) tucked in behind a specially rigged pace vehicle.

Mike

[padgett]

On level ground, the only resistance is drag. Knew some had pedaled over 120 behind trains almost a century ago. With right "draft" would require almost no effort at all.

Observation I was making wasn't that the drag would not be higher as speed rose but rather that the drop from 60 to 70 for a "C" engine seemed more than expected. Add in the very high MPG values that a SII 3800 records (saw 40-42 mpg instantaneous several times at 60 mph - two different cars - on flat stretches with 2001 Avis LeSabres. Under similar conditions my Reatta shows 31-34 mpg.

Made me wonder if was at least partly due to the 55 mph national speed limit that was in effect when the Reatta was built. Know that the exhaust systems are better and the air cleaners much larger on the late cars. Suspect the cams are more agrresive also. Anyone know if the SII has a different combustion chamber ?

[Guest Reatta1]

Padgett, what year is your Reatta? What brand o2 sensor are you using? I have never changed the o2 sensor on my 88, have had the car 2+ years and currently has 69k. I consistently get 28 to 31 mpg on the road at 70mph average spd. City driving gets me 22 to 24. Have seen over 70 mpg instantaneous when coasting from highway speed coming into a reduced speed zone. What were the driving conditions that generated those figures?

[padgett]

Mine is an '88 with about the same miles and also has the factory PROM update ANCX (corrected low reporting of MPG). Florida also has a number of long flat stretches. The readings reported are the range seen on at least three times after stabilizing for a half mile or better.

The O2 sensor is a Bosch 12014. RapidFire #3s, stock otherwise. Run on lowest price 87 octane. 225x60x16 tires (less than 3% different diameter than 215x65x15). Orlando is about 100 ft above sea level. Car is garaged. Thinking about a Jacobs.

Filled up several days ago and had to go to Kissimee yesterday (about 1/3 Interstate, 1/3 highway with traffic lights, 1/3 city and showing 20.3 MPG average after 60 miles. I generally use the cruise when possible but tend to be "spirited" out of TCDs.

Sounds like your car is already optimized

[Guest Reatta1]

I think mine is still all factory original as it came off the dealer show room. The computer readout for mpg has never shown me higher than 21.8 mpg. I always figure my mileage off gallons used to miles driven. It still has factory size tires and I use Arco regular gas almost exclusively. On the highway I use CC as much as possible. The best I've gotten on the road was 31.2 mpg. Was a little over 400 mile jaunt and used less than a full tank of fuel.

[padgett]

Interesting. What is your PROM code (is ED99 in the ECM data area) ?

BTW the 88 factory PROM had a defect and would record MPG 10-20% low. That is one thing the ANCX replacement corrects. Mine reads close to what I measure at the pump.

[Guest Reatta1]

Couldn't tell you that. Do you find that in the diagnostic mode? I'm waaaayyyy out in left field when it comes to the computer stuff.

[padgett]

On the CLIMATE touchscream with key on (engine does not need to be running) press both OFF and WARM at the same time. After a few seconds you will hear a double beep and it will switch do diagnostics mode. The SES light will flash.

After cycling through any stored trouble codes the display will stop at "ECM ?". Press YES. Next you will see ECM DATA. Press YES again. ED01 (TPS) will display. Press NO once and it will loop back to ED99 - PROM ID. This will be a four numeric digit value (ANCX is 3534, ANBM (stock 88) is 2544).

Every Reatta really needs a factory service manual - an extensive description of the computer system starts in section 8D. Even a "New Product Information" manual for the 88 has this and the 5E1 section on the TEVES but a "Final" has everything.

Just noticed that both a NPI and a Final are on e-bay right now as is a TEVES training manual. The latter is interesting as it references over 100 pages. The 5E1 section in the 88 FSM is 109 pages - not certain how it could have less.

Personally have been surprised at the high bids I see for NPIs since they are typically about half the size of the Final and includes only what is different from the previous year - not everything. For example the 88 NPI has no section 7 (Transmission) or 10 (Body - doors, seats, sunroof).

I suppose Mr. Barnum was right.

[Guest Reatta1]

Checked it and came up with 2544, original. Where does one get the ancx prom and am I better off having the dealer service dept. change it for me? As mentioned, I am total greenhorn when it comes to car computer stuff.

[padgett]

ANCX is p/n 16123488 and GMPD had them the last time I looked for a hair under $50 including their idea of shipping. Will still have the stock fan settings.

To get to ECM you drop the black kick panel under the glove box and it is mounted vertically to the side on the right of the programmer. Dropping the ECM and changing the PROM takes about 15 minutes if you are slow like me. Like many other things the procedure is completely explained with pictures in the service manual.

[Guest Reatta1]

Appreciate the help. Will stop by my dealer and see if they can come up with it. Sounds like changing it is something I should be able to handle. My biggest problem with working on cars is that I'm missing four fingers on my right hand. The result of an industrial accident some 25 years ago. Is why I scouted a GOOD dealer service dept for the Reatta. Everything else goes to a good friend who has a shop.

[Guest Reatta1]

Padgett, ordered the new prom yesterday. My dealer parts man said I got one of the only two left listed nationwide. Course that is GMPD. Don't know if there are other sources.

[padgett]

Well if they run out it is easy to reprogram any 5B (3800 family) PROM from a different car. The PROM itself isn't a problem - is a standard 27C256 - but the resistor pack (the other half of the blue memcal aka calpack) is said to be specific to the 3800.

Once you have a dump of the code such as the ANCX (what I use as the basis for my 88), it is easy to reprogram the PROM from say a '90 Oldsmobile with 3800 to be a Reatta and I would expect the yards to have quite a few.

My problem is that I never get the time to wander in junkyards any more.

[Guest Reatta1]

Padgett,

New prom came in yesterday. Got installed yesterday afternoon. Looking forward to seeing what difference it makes. Did get one surprise. Was expecting in neighborhood of $50 for prom and it was $70. OUCH!!