: GUZZLING GAS!!! 2000 Deville...

01-10-13, 05:59 PM
17.6 MPG avg. Any thoughts???

01-10-13, 06:27 PM
I looked up mpg. for 95 dev,. it shows 15/22, so your doing o.k.


I looked up mpg. for 95 dev,. it shows 15/22, so your doing o.k.

It was actually for a 2005

01-10-13, 09:37 PM
Under what conditions ?? What car, what engine ? (assuming that you're running the recommended 87 octane Top Tier fuels)

City = 11 to 16 mpg
Suburban = 15 to 19 mpg
Open highway, long run = 25+

Combination city/suburban, winter, stop/go, idling - 17.6 long term average is exceptional - Don't reset the long term average at every fill - let it run forever. Average

What is the EPA window sticker mileage rating for your car ?

01-14-13, 03:57 AM
I don't know, that sounds like the average of a city/suburban car. If you drive on an interstate, you'll see much better results. No, it's not going to get 30MPG average, but it gets impressive mpg for a 4,000+lb 4,600cc V8.

Manic Mechanic
01-14-13, 02:01 PM
I don't know enough about you and your car but a bad MAF will do it. Had one on a customers 2002 base DeVille that was getting sub-par mileage, about that, and lacked power. Until I got mine I thought that's how they ran and wouldn't consider owning one. After driving mine fixed and being shocked at the power and mileage difference I looked into the customers car. It didn't have any MAF codes, or any engine performance codes for that matter but the fuel trims were a little off. I swapped my MAF onto it for a quick diag and it "fixed" it. So I ordered them another MAF and they're much happier with the car now. I've seen the same thing on a few GM cars and trucks over the years.

Get on a flat hiway with little wind doing 55 and watch the instant MPG reading. It should be well above 20. Mine gets 30 without a locked convertor and another customer's DTS gets 30 locked.



BTW cleaning the bad unit didn't help.

01-14-13, 04:44 PM
Be careful when simply swapping a MAF - it's an expensive easter-egg. Look at the FPR, IAC, and vacuum systems first.

01-16-13, 03:59 PM
If it is the MAF the. Oem Delphi MAD can be found on amazon for 75 dollars atleast that's what I paid a few weeks ago

03-02-13, 03:35 PM
What is a MAF?
I have somewhat of the same issue.


03-02-13, 03:45 PM
MAF = Mass Air Flow Sensor. I believe on your engine it may be bolted to the TB and the intake ducting (#3) is clamped to it.


#4 in this view. #7 is the MAP (Manifold Absolute Pressure) sensor.

03-03-13, 11:52 AM
What is a MAF?

Mass AirFlow sensor. Uses heated resistors placed in the intake airflow stream - airflow changes affect the resistance values - to aid in engine power and fuel trim adjustments sent to the fuel injectors by the PCM (Powertrain Control Module). Included with or near the MAF is an IAT (Intake Air Temperature) sensor, also used in fuel trim calculation.

Acronyms - use the sticky post just above this for info. Read all the stickys ...................

Manic Mechanic
03-03-13, 08:59 PM
Since I got my car running last Saturday and then started really driving it Tuesday after renewing the registration I've been getting another 2 MPG due to my convertor locking. I replaced the TCC solenoid and had the trans overhauled with a clutch and seal kit and replaced the torque convertor while I was overhauling the engine. I had to have my heads milled just to clean them up so the compression is up a hair but the main improvement is the locked convertor. Now at 55 MPH I'm spinning just 1500 RPM and achieving 32 MPG on flat ground. My average which was reset completely when I filled up Tuesday is now up to 20.8 with daily driving, stops and traffic between 2-5 mile stretches of highway etc. I use hyper-mileing techniques within reason though.


03-05-13, 12:46 PM
Here's the speed/rpm tables for the VIN Y (3.11) and the VIN 9 (3.71) transmissions with TCC engaged above 43 mph.