Topic: Watching MPG go right down to obscene lows or WTH is going on??

[JimmyBaja]

For what it's worth, I have been keeping track of AVG mileage now since the SC install. Checked & reset after each fill up. I couldn't believe that my AVG mileage went from 25.5 to 30-31 under the same driving conditions (commute) so I checked it manually with a calculator. Turns out the DIC says 30.2 & my calculator says 24.3. I only checked it manually once before & it was also lower than the DIC but don't remember how much exactly, I think maybe 4 or 5 MPG.

[JRinKY]

JimmyBaja : For what it's worth, I have been keeping track of AVG mileage now since the SC install. Checked & reset after each fill up. I couldn't believe that my AVG mileage went from 25.5 to 30-31 under the same driving conditions (commute) so I checked it manually with a calculator. Turns out the DIC says 30.2 & my calculator says 24.3. I only checked it manually once before & it was also lower than the DIC but don't remember how much exactly, I think maybe 4 or 5 MPG.

If you are basing that on a single fill up, you may not be calculating the true mileage. The degree of level of the car can easily change the pump shutoff by a gallon or more. I check my indicated mileage fairly regularly against calculated mileage, and while individual tankfuls will sometimes vary significantly, an average over several tanks is quite accurate.

[Jackknife]

If you are basing that on a single fill up, you may not be calculating the true mileage. The degree of level of the car can easily change the pump shutoff by a gallon or more. I check my indicated mileage fairly regularly against calculated mileage, and while individual tankfuls will sometimes vary significantly, an average over several tanks is quite accurate.

How about ACTUAL gallons (pump read), and ACTUAL miles (odometer read).

[tazz]

What he's saying is even then the Actual amount of fuel before shut off can vary unless you always use the same station as well as the same pump each time and that can throw off the avg MPG calculation since it could vary by 1 gallon or more less to shut off.
Really it shouldn't really matter to begin with since your taking an average over time not just a few fillups when doing it manually. 

[tazz]

Getting back to what his problem is or might be if he is actually seeing a decrease in MPG could likely be the main 02 sensor not working properly for some reason. I'm sure there's a limp mode for the WB in where if it stops working properly it will default to limp table and be set at a safe limit like 11-12AFR or whatever the lowest AFR the ECM commands at WOT no matter what the load.  I could be something else altogether with some other sensor throwing everything else off?
I'm very curious to findout exactly what is causing the problem.

[scanner]

Shoot, I didn't know I was going to need a paracute! (for all that talk about we jumping to conclusions....from great heights too I suppose)  Sheesh, Fill the tank reset the mileage meter, drive & enjoy. Fill the tank reset the mileage meter, drive & enjoy. Fill the tank reset the mileage meter, drive & enjoy. Fill the tank reset the mileage meter, drive & enjoy. Opps, if you see a difference take note of driving patterns and habits and changes made. Fix if necessary. No paracute required. Fill the tank reset the mileage meter, drive & enjoy.

[DeepBlueGXP]

[JRinKY]

The radical changes in average MPG readings indicate a problem with the computer systems in the car. It is physically impossible for actual average MPG to vary that way. I made up the actual numbers, but this scenario is what I interpreted from the descriptions:

If the average MPG after 100 miles is 25, 4 gallons of fuel have been used.
If the average MPG after 125 miles drops to 10, 12.5 gallons have been used. 8.5 gallons in 25 miles. The average MPG for that 25 miles is 2.9.
If the average MPG after 200 miles is back to 25, 8 gallons have been used, which is impossible, unless the engine produced 4.5 gallons of fuel in 75 miles.

[Chemist]

The radical changes in average MPG readings indicate a problem with the computer systems in the car. It is physically impossible for actual average MPG to vary that way. I made up the actual numbers, but this scenario is what I interpreted from the descriptions:

If the average MPG after 100 miles is 25, 4 gallons of fuel have been used.
If the average MPG after 125 miles drops to 10, 12.5 gallons have been used. 8.5 gallons in 25 miles. The average MPG for that 25 miles is 2.9.
If the average MPG after 200 miles is back to 25, 8 gallons have been used, which is impossible, unless the engine produced 4.5 gallons of fuel in 75 miles.

Ho, ho, ho
It's magic you know
Never believe it's not so.
It's magic, you know
Never believe it's not so!   (with apologies to E.L.O.)



Something _is_ amiss somewhere in computer land. 

[Greggars]

Way off topic, but the song is Magic by Pilot not ELO.

As for mileage, my '08 stock GXP has averaged over 30 MPG over the 14500 miles that I have on it. For that reason, I think that I will stick to stock!!

[JimmyBaja]

I never did trust the DIC/computer, even on my GMC truck before it never matched the odometer/gallons calculator method, the DIC always said I was getting better mileage. Makes you wonder if the car builders do that on purpose to make you think you are getting better mileage than you actuly do.

[Aspenrose]

Ok, disregarding the MPG issue-reflashed by Vector ECM is back in the car, and after the short drive to work, have 2 codes thrown, P0131 and P0171. With it running rich for 3 weeks-I'm thinking O2 sensor may be need to be cleaned or replaced, plugs possibly fouled? It is running way lean, had to watch it at every stop that it didn't die.

[Critterman]

OBD-II Description P0131 - Oxygen O2 Sensor Low Voltage (Bank1, Sensor2)

OBD-II Trouble Code: P0171 System Too Lean (Bank 1)

My memory isn't working right now, but I think you went with a high flow cat when you put on the header.  That could cause the 131 code.  The 171 I would be worried about, I would not run it hard until you get that looked at.

[Aspenrose]

OBD-II Description P0131 - Oxygen O2 Sensor Low Voltage (Bank1, Sensor2)

OBD-II Trouble Code: P0171 System Too Lean (Bank 1)

My memory isn't working right now, but I think you went with a high flow cat when you put on the header.  That could cause the 131 code.  The 171 I would be worried about, I would not run it hard until you get that looked at.

You are bang on-Solo Cat, so for at least that one, it looks like I'm still stuck with trying to move the sensor.

[Chemist]

Way off topic, but the song is Magic by Pilot not ELO.

As for mileage, my '08 stock GXP has averaged over 30 MPG over the 14500 miles that I have on it. For that reason, I think that I will stick to stock!!

My bad. Mixed up "Magic" and "Strange Magic" (which _is_ ELO ).

[DeepBlueGXP]

I believe the malfunctioning/02 code may cause the lean condition.

[tazz]

A vacuum leak would also cause a lean condition and rough idle where the car would want to die.

[tazz]

Way off topic, but the song is Magic by Pilot not ELO.

As for mileage, my '08 stock GXP has averaged over 30 MPG over the 14500 miles that I have on it. For that reason, I think that I will stick to stock!!

You think 22MPG is bad how about my daily driver 03 Supercharged Ford Truck right at 12MPG Avg alot of times 10MPG but I also was in boost at every stop.  Good thing I only needed to fill the 25 gal tank every week.  There when fuel was over $4 a gal I was spending $450 a month on fuel plus still making a truck payment of $600 a month thought it would never end.

[scanner]

The O2 circuit should be checked for electrical problems. The fuel pressure should be checked too.

Regarding the Magic. There are two kinds, FM & PFM.

Freaking Magic and Pure Freaking Magic.

Personally I like PFM the best.  If the vehicle has no mods the MPG display in the IP are usually accurate. It runs on PFM with information trading between control modules based on a model.  The model is a factory build.  Mods may or may not impact the PFM calculations.   

Did I mention, reset, fill tank, Drive & Enjoy?