Sudden Drop In Gas Mileage 4.8IS

[cannan]

My 06' 4.8is with just over 90,000 miles. I have owned the car almost 4 years and have always seen roughly 390-400 miles on a full tank of gas, but my most recent two fill-ups have only been netting me 315-320 and that is with less than 30 miles left on the tank according to the OBC. Essentially a drop off in almost 100 miles.

My driving habits have not changed. Virtually all driving is around town stop and go. I have not thrown any codes or experienced anything abnormal. Only real change in conditions is the cold ass weather we've been having.

Just seems odd to me, no?

[jsoto]

Winter fuel ?

[upallnight]

An engine needs to run a little richer when it first starts up especially in cold weather. Back in the days of carbs, a choke was use to accomplish the required rich mixture, nowadays the computer control the injection cycle to accomplish this rich mixture. If you have a piece of software like Torque and an OBD II adapter you can time how long it take to go from open loop cycle to close loop cycle.

[cannan]

Originally Posted by upallnight

An engine needs to run a little richer when it first starts up especially in cold weather. Back in the days of carbs, a choke was use to accomplish the required rich mixture, nowadays the computer control the injection cycle to accomplish this rich mixture. If you have a piece of software like Torque and an OBD II adapter you can time how long it take to go from open loop cycle to close loop cycle.

I figured it had something to do with the cold weather it just seemed like a significant drop off even for cold weather. Thanks for the insight, I don't have any software but my local indy is really helpful so I'll check with them.

[four.8is]

You say you've owned the car for 4 years and this is the first time happening?
How about the other 3 winters? Any change then?still ,100 miles is too much to drop over cold temps only..I know on my E39 I changed my O2 sensors(just because-nothing wrong with the car at the moment), and the MPG went up considerably..not saying that's your problem just something to think about...

[upallnight]

Originally Posted by four.8is

You say you've owned the car for 4 years and this is the first time happening?
How about the other 3 winters? Any change then?still ,100 miles is too much to drop over cold temps only..I know on my E39 I changed my O2 sensors(just because-nothing wrong with the car at the moment), and the MPG went up considerably..not saying that's your problem just something to think about...

In order to go from open cycle to close cycle, the 02 sensor has a heater in them to speed up the cycle, but as with any electrical heater, over time they lose some of their efficiency. The heater may be taking a longer time to heat the sensor, or the extreme cold may cause the heater to take additional time to bring the 02 sensor to close loop.

This winter is probably the worse winter that the States has experience in a long while.

[four.8is]

Originally Posted by upallnight

This winter is probably the worse winter that the States has experience in a long while.

I wish we were getting some snow in Seattle...

[TerminatorX5]

how old are your spark plugs? how often are you changing the oil? those little things, while keeping the engine within the wider spec range, may influence the MPG... I remember i improved the MPG on mine when i did the engine flush - went from 12 MPG in january of 2013 to 16 MPG right after an oil change at the end of March, on a trip to Orlando, 95% highway hauling, pulled 17.8 MPG in the beginning of April, at the beginning of May started the engine flush and stayed consistently not less then 17MPG, had couple oil changes with engine flush before october, stayed consistently in 18MPG, with a peak at 19 MPG, and in november dropped back to 17MPG, and now at 16MPG... due for another hot oil change, and it seems that another engine flush might be in the cards... but in the winter the mileage seems to suffer...

[upallnight]

Originally Posted by four.8is

I wish we were getting some snow in Seattle...

You can have our, free you just need to haul it away.

[four.8is]

Originally Posted by upallnight

You can our, free you just need to haul it away.

Set aside 6000 pounds I'll haul it with my x
Seriously no snow the past few years...in Oregon it's a mess on the streets ..