fuel mileage

[newfie6719]

my 2005 i6 is going threw 26/L per 100k suv got 105 thous k on it noticed this sence the pcm was tuned. today going to put the stock pcm in and is if it gets better. at the rate it's going threw gas think should be getting some sort of smell if it was unburnt fuel and the suv runs great had the suv about 5 months now so really don't know history of plug or o2 sensor all oils and fluids been changed tb cleaned a couple times air filter good. no cel lights or stored codes. guess i'll report back after running the stock pcm for awhile. any ideas would be great thanks.

 

[meerschm]

CalculateMe.com - Convert Liters Per 100 Kilometers to Miles Per Gallon (US)

close to 9 mpg.

Wow. seriously. hope that is around town in traffic.

I would also look very closely at the brakes. and tire inflation.

one thing at a time if you want an answer, is everything stock? is this measured, or via the trip computer?

 

[newfie6719]

CalculateMe.com - Convert Liters Per 100 Kilometers to Miles Per Gallon (US)

close to 9 mpg.

Wow. seriously. hope that is around town in traffic.

I would also look very closely at the brakes. and tire inflation.

one thing at a time if you want an answer, is everything stock? is this measured, or via the trip computer?

everything is stock except the pcm and vette servo yes set trip meter after fillup and it is mostly around town driving but still there's no way it should be close to that brakes are all new no dragging new tires @35psi in them.

 

[Hypnotoad]

I thought my mileage was bad at 16-18 mpgs. I've got a totally stock short wheel base with 3.73 gears and I drive like a man, if your looking for any comparisons.

 

[newfie6719]

I thought my mileage was bad at 16-18 mpgs. I've got a totally stock short wheel base with 3.73 gears and I drive like a man, if your looking for any comparisons.

and that's the thing that's driving it easy to see what i was getting out of a tank thought it was me driving it harder the tank before lol

 

[Dad-O-Matic]

What about your temp?
Does the temp gauge read straight up at about 210* f (100* C)?
Do you have a way to check actual temperature (Scan tool or Torque)?

I think the most common cause of poor gas mileage is a stuck open thermostat, but you should be getting a P0128 code if its been stuck for very long.

 

[newfie6719]

my temp needle is straight up and using scan xl going to have to take it for a drive then check i'f i remember correctly it was 197 last time i checked

 

[meerschm]

why call it mileage, if you calculate fuel use rate as liters per 100 kilometers?

fuel efficiency,

(I know this is kind of a "why do you drive on the parkway and park on the driveway")



as an academic hijack to the side, I stumbled on this:

http://energy.umich.edu/info/pdfs/Fuel Efficiency Horizon FINAL.pdf

 

[newfie6719]

what's the best thing to monitor with scan tool and obdwiz to see if values are out of wack were should i start

thank

 

[Mypetropig]

I would start looking at the 02 sensors. I am not sure of the value/reding you should see but I do know they should fluctuate quickly. A lazy sensor, one that reads slowly, can affect mileage. If it is lazy and you decide to replace it, only use AC-Delco brand.

 

[CaptainXL]

what's the best thing to monitor with scan tool and obdwiz to see if values are out of wack were should i start

thank

Excessive fuel consumption can result from...

1. Clogged air filter
2. Poor or no spark
3. Restricted catalytic converter or pipe muffler
4. Low tire pressure
5. Stuck fuel injector
6. Stuck thermostat
7. Malfuntioning engine coolant temp sensor
8. Brakes binding

I would check ECT and manifold vacuum to start. Then the O2 and fuel trims. If there are codes look at them first.

 

[WarGawd]

I would start looking at the 02 sensors. I am not sure of the value/reding you should see but I do know they should fluctuate quickly. A lazy sensor, one that reads slowly, can affect mileage. If it is lazy and you decide to replace it, only use AC-Delco brand.

To that end, I logged about an hours worth of data with my ScanXL and OBDWiz just prior to changing out my bad t-stat this Tuesday. I had been experiencing a more than expected degradation in my own fuel efficiency as the avg temp got cooler in recent weeks. When I bought mine in July, I was getting ~16.5L/100km with a 65/35 city/hwy mix, and generally pretty aggressive driving coupled with a fair bit of idling in the city. Previous owner had DIC indicated overall efficiency of 15.4 L/100km over a recorded 9999.9L of consumption (about 65000 km worth of history) living in a rural area where I expect his highway driving proportion was a fair bit more than my own. My conclusion is that in the summer, the sticky t-stat was less of an issue because hotter ambient temps let it run hotter - lately efficiency has degraded to 18.5-19ish L/100km.

I've only put 100km on it since then, prob will be over 500 by next Monday - evaluation of any improvement in efficiency is ongoing, and in a day or two when I get a chance I will repeat the data logging route for comparison. Meantime I am definitely interested in the outcome with your stock PCM - I have a PCM4 tune waiting to go in once I know what the baseline fuel effiiciency really is, so I can compare the two.

The zipped file is 1.3Mb, so I can't attach it here - if you want it, PM me with an email address. File has both .csv for import to spreadsheet, as well as the .tdl propietary log files that you can play back directly in OBDWiz

Cheers

PS - if you follow my signature, it'll show you all my consumption data since I bought it, 77 fillups totalling 2700 L over 15000 km driven, with a pile of notes made along the way.

 

[newfie6719]

this is after some logging on obdwiz

 

[CaptainXL]

The first think that strikes me is that your alternator is putting out 16 volts! The limit is 14.5. Possibile faulty voltage regulator in the alternator.

You are also borderline with the coolant temp. Minimum temp for closed loop operation is 188-190 F. Normal highway temp is about 200 F. I would definitely look into changing the thermostat if the temps don't come up after driving for a while. If it was changed recently I bet it was a lower than standard temp tstat.

 

[meerschm]

The first think that strikes me is that your alternator is putting out 16 volts! The limit is 14.5. Possibile faulty voltage regulator in the alternator.

You are also borderline with the coolant temp. Minimum temp for closed loop operation is 188-190 F. Normal highway temp is about 200 F. I would definitely look into changing the thermostat if the temps don't come up after driving for a while. If it was changed recently I bet it was a lower than standard temp tstat.

you could check the record of voltage. did the high reading happen once, and if so, what else was happening. could just be a blip.

does the temp change? mine tends to trace up and down a notch or so. do you see it track up from cold after you start?

Is the O2 sensor supposed to act like that?

 

[CaptainXL]

Looks like a spike is what it looks like. The mean voltage and min voltage are outside norms as well. Max voltage according to the service manual is 14.5 volts nominal. The alternator needs to be checked.

The o2 sensor is switching just fine between 0 and 900 millivolts. But it looks slow at maybe once every two seconds. I would change it. They only last 100k anyways.

Short term fuel trim should hug closer to 0 than what it presently is. Wild swings from -20 to +20 could indicate a fuel or ignition issue. But if your o2 sensor is slow then that would be the cause.

I would check your misfire data just to be thorough. Mode 6.

 

[newfie6719]

thanks for the reply the temp ranges from 187 to 195 after warm mostly on the 192 as for the volts i'll look at that part again. looking at some other logs the thing i did notice my Ignition timing advance for No. 1 cylinder never drop below -10 . as for the o2 sensor it may never have been changed i'll try to check for missfires to thanks

ok just checked the input volts and they are around 15.5v steady

i'm starting to think it's a partly plugged cat because every now and then i get an bad smell from the exhaust and for the dealer to warranty it look about 200 bucks if that not it

 

[hockeyman]

I'm averaging 15-16 mpg's, and I was almost too embarrased to admit it when I first got my Envoy back in July. I rarely used my A/C in the summer, except the times when wife was along for the ride...

Checked my air filter last month and it's still somewhat clean. I will change the thermostat when I do a coolant flush in the spring.
My fuel filter looks as though it's been there for a while (maybe stock), so I'll replace that too.

 

[WarGawd]

I'm averaging 15-16 mpg's, and I was almost too embarrased to admit it when I first got my Envoy back in July. I rarely used my A/C in the summer, except the times when wife was along for the ride...

Checked my air filter last month and it's still somewhat clean. I will change the thermostat when I do a coolant flush in the spring.
My fuel filter looks as though it's been there for a while (maybe stock), so I'll replace that too.

Better than my overall average - what city/hwy proportion do you have?

 

[newfie6719]

so checked the plugs yesterday looks like orginal plugs going to change them tomorrow air filter looks in good condition couldn't get the o2 sensor out. now on the 05 were do you check fuel presure cann't seem to find any info to where to hook the gauge to thanks for the help.

a test at wot

 

[newfie6719]

will new plugs in priced new 02 sensor and thermostat price around here is nuts. so if needs it going to order online check the temp on the front of the cat and back of the cat its way hotter at the back so seems like the cat is working going to get a fuel pressure test done tomorrow and a scan see if the shop can find anything. puzzled seems a bit harder with stock pcm in so know it's not in the tune.

@ $1.30 liter it's killing me lol

 

[newfie6719]

lets see had in the shop they scanned it did vacuum leak check couldn't find anything. so today went and got the cat removed not sure might be partly plugged and remove the garbage can on the back. so i guess time will tell if it's any better on fuel fingers crossed. now the ? is when it throws a cel light have anyone had a success using the sparkplug non fouler method on the downstream 02 sensor to keep the light from coming on thanks.


guess i'll let yea know got to way till next week to get the fouler plugs