Change in MPG Rating from 1995 to 1996

[RichieR]

Hello everyone:

We have 2 Cadillacs in my family - a '95 Eldorado and a '97 Deville, both with the 275 HP Northstar.

I was watching the videos that I received with both cars and I noticed that the MPG Ratings are different on the '95 & '97.

I then looked up the MPG ratings in the original Cadillac Brochures for '95, & '96 and I noticed that all the '95 Northstars had MPG ratings of 16MPG in the city and 25MPG on the highway. I then looked at the '96 brochure and I noticed that the MPG ratings for all Northstars were improved to 17MPG in the city and 26MPG on the highway (it was the same in '97). Weren't the Northstar Engines identical in those years? I know that '95 was the first year the horsepower was increased by 5 HP to 275 and 300 hp (from 270 & 295 previously). Did Cadillac just rerate the MPG on the Northstar, or was there a change to the engine that improved the MPG ratings?

Just curious.

Thanks,

Richie.

[Cadillac Jim]

There were a number of changes between the 1994 and 1995-1999 Northstars. The fuel injection was changed, and that accounts for the extra 5 hp and possibly a gas mileage improvement. The EGR was redesigned, which could account for a slight improvement in EPA gas mileages. Others more knowledgeable than I can give you more information.

You will get about the same difference by putting 32 psi in your tires instead of 30 psi, and also perhaps using nitrogen in your tires instead of air. Do you see any difference between the gas mileages in your 1995 DeVille and 1997 Eldorado, with the same driver?

Recent posts here show that the experience here is that you get more miles per dollar by staying with premium fuel than by trying the intermediate grade or 87 octane because you will experience gas mileage differences that will slightly more than offset the difference in prices.

If your fuel economy is consistently lower than EPA, and/or if you experience performance problems at higher RPM or full throttle, you should look at your catalytic converter or exhaust system obstruction, particularly if you have a 2002 or early 2003 model (but I do see from your info that your cars are 1995 and 1997 models). Of course, the first thing to do when you have any complaint is to check the codes.

[Ranger]

Also remember that MPG ratings are a "fleet" average. Not necessarily for that particular car. Not sure how the "fleet" changed from '95 - '97 but that may have something to do with it.

[Bill K]

I have noticed that my milage increases with each of the followings changes.

1. Brake w/ right foot instead of left.

2. Avoid the drive thru lane and just go inside to conduct business.

3. Have my wife in the car w/me.

[RichieR]

There were a number of changes between the 1994 and 1995-1999 Northstars. The fuel injection was changed, and that accounts for the extra 5 hp and possibly a gas mileage improvement.

However, the horsepower was the same in 1995 & 1996, etc. however, the MPG rating was lower in 1995 than 1996. That's what's interesting. If the MPG Rating had changed from 1994 to 1995 (when the horsepower changed), that would make more sense.

It's very hard to monitor city MPG, because there are so many variables (amount of time you sit in traffic, etc.). However, I do have to say that the highway mileage is slightly better with the '97 Deville than the '95 Eldorado. I usually get anywhere from 27.5 to 28.5 MPG in the '97 Deville and anywhere from '26.5 - 27.0 with the '95 Eldorado - and the Deville is a bigger car.

I wonder if they made some subtle changes to the Northstar System in 1996 that improved fuel economy, because they did bring the point out on the '97 Deville Video Tape that estimated highway driving range was 520 miles (26 MPG X 20 gallon tank) compared to 500 miles with the '95 Eldo (25 MPG X 20 gallon tank).

[JasonA]

Nothing that we know of, besides the OBD-II, changed between 1995 and 1996. I'll speak for the group saying that as far as we know, the 1995 Northstar is exactly the same as the 1999 Northstar. Engines prior to 1995 were just ever so slightly different (speed density vs. MAF, intake manifold differences) and engines from 2000 and later were moderately different (cylinder head differences, PCM changes, etc). There's no singular change that I can think of that happened between 1995 and 1996 to account for the fuel mileage re-rate.

[BodybyFisher]

I am not sure if it would make a difference but from 95 to 96 the PCM was substantially upgraded according to the new car brochure I have, when I find it I will post the text that describes it

[JasonA]

BBF, I bet that's to accomodate the OBD-II software/programming. It's possible the engine calibrations were changed at that time as well.

[The Fred]

Plus the mileage ratings in the USA are a big pile of horse waste

Ratings I forgot to say estimates

[JimD]

Guesstimates.

[BodybyFisher]

I have been racking my brain to remember where I saw the 1996 change related to the PCM.... Here is what I think contributed to the fuel efficiency change from 95 to 96:

*A more powerful Powertrain Control Module (PCM) with micro-processors monitored and directed DeVille engine/transmission operations.

* Clock speed of the PCM microprocessor was increased from 2.1 megahertz to 3.4 megahertz, which improved processing time 63 percent.

* Memory size was increased from 64 kilobytes to 96 kilobytes per microprocessor, allowing the PCM to provide more software functionality (probably for OBD2).

*For improved throttle response and reduced exhaust emissions, a mass air flow sensor was added. This sensor continually measured the volume of air entering the engine and supplied that information to the PCM.

*In addition, the PCM was moved from the passenger compartment to the air cleaner housing. This move enhanced engine harness reliability by reducing wiring lengths and minimized the number of wires passed through the front of the dash. (the faster processors required better cooling I am sure!, this is why I for one am reluctant to screw with the AIR BOX by putting an EXTERNAL K&N filter on that does not suck air over the PCM)

*Improved design precision fuel injectors delivered precise fuel metering, which contributed to more efficient fuel control.

Reference: http://www.100megsfree4.com/cadillac/cad1990/cad96d.htm

[ted tcb]

Of course, we're assuming that changes to the N* emission controls and engine management systems improved the gas mileage.

Statistics are a manipulative tool ... ask the pollsters.

Testing criteria evolves and standards change.

The exact same vehicle can have varying results depending on when the tests were performed and what criteria was involved.

Look at the government's E Star ratings for hydro consumption on appliances as an example.

I have noted that the very same front load washer went from 360 kilowatt hrs/yr down to 250/yr, and then to 180 per/yr.

The testing facility reduced the standards to a smaller weight load, shorter wash cycle, and lowered the standard water temp.

My point is that the 95 and 96 cars may actually consume the same amount of gas, but the testing standards are not static .

[JasonA]

*For improved throttle response and reduced exhaust emissions, a mass air flow sensor was added. This sensor continually measured the volume of air entering the engine and supplied that information to the PCM.

*Improved design precision fuel injectors delivered precise fuel metering, which contributed to more efficient fuel control.

Reference: http://www.100megsfree4.com/cadillac/cad1990/cad96d.htm

Ah ha. I thought the MAF sensor was added for 1995. I guess it was added for 1996. Can someone with a '95 model confirm that there is no MAF for '95? That, and the different fuel injectors, would make sense to me as being the difference between 95/96.

[RichieR]

I am not sure if it would make a difference but from 95 to 96 the PCM was substantially upgraded according to the new car brochure I have, when I find it I will post the text that describes it

That's an excellent point. I'm sure that the upgrade to OBD II in 1996 accounts for the improved mileage ratings. I was comparing the engines from 1995 to 1996 (which were the same) and I forgot that the electronics changed.

Also, I'm sure that the change in the design of the fuel injectors also improved gas mileage.