Huge increase in MPG??

[DenaliHD66]

No idea how, I haven't cleaned the air intake/throttle body, anything since last year around this time, only thing different about the truck is I put on 265/65/17 Michelin LTX MS2 tires. These are larger than the previous 255/65/17 Duelers I had on there, which were run while bald.

Anyway, recently, my MPG has gone from about 13.1 about 5 weeks ago, and today I filled up and recorded the highest ever MPG at 17.1. Nothing has changed about my driving style or my routes. I drive the same places week in and week out. My O2 sensor is the original with original exhaust manifold, 110k miles, is a lazy O2 sensor that has been bathed in seafoam and cleaners all these years to credit for ever increasing MPG?

 

[Phantom]

No idea how, I haven't cleaned the air intake/throttle body, anything since last year around this time, only thing different about the truck is I put on 265/65/17 Michelin LTX MS2 tires. These are larger than the previous 255/65/17 Duelers I had on there, which were run while bald.

Anyway, recently, my MPG has gone from about 13.1 about 5 weeks ago, and today I filled up and recorded the highest ever MPG at 17.1. Nothing has changed about my driving style or my routes. I drive the same places week in and week out. My O2 sensor is the original with original exhaust manifold, 110k miles, is a lazy O2 sensor that has been bathed in seafoam and cleaners all these years to credit for ever increasing MPG?

Could be the gas. Stations switching to the summer formula.

 

[DenaliHD66]

That doesn't happen around here until mid June. As far as I know, 10% ethanol remains all year round. What's the difference between winter and summer gas anyway? It used to be that ethanol was only added in winter (which is stupid given its tendency to accumulate moisture).

 

[dmanns67]

I have also noticed an increase in my highway gas mileage here in the last 2 weeks. I was averaging 15.5 to 16, now I am around 17.8 to 18.5. I just assumed it was the gas.

 

[Matt]

The weather is warmer and the gas is changing. I noticed going from 11/12 to 16+ in the last couple of weeks.

 

[gmcman]

My O2 sensor is the original with original exhaust manifold, 110k miles, is a lazy O2 sensor that has been bathed in seafoam and cleaners all these years to credit for ever increasing MPG?

O2 sensors become lazy generally around the 80K mark, not set in stone though. When I replaced mine very late in the game (around 180K) my combined MPG after 1 week went from 15-16 to around 17.5-18.

 

[meerschm]

O2 sensors become lazy generally around the 80K mark, not set in stone though. When I replaced mine very late in the game (around 180K) my combined MPG after 1 week went from 15-16 to around 17.5-18.

did you have any trouble getting the O2 sensor out?

I have just shy of 150k, and the mpg has been a little off.

guess I can look into how it is working

 

[gmcman]

did you have any trouble getting the O2 sensor out?

I have just shy of 150k, and the mpg has been a little off.

guess I can look into how it is working

Not at all, with the O2 socket (7/8) it came right out. With a cold engine, I would let it run for about a minute or 2 then let it sit for a couple min. With the heat shield in place you need an O2 socket, the offset socket worked fine.

To check it's operation with a scan tool you want at least a 1Hz refresh at the slowest, mine was averaging about 1.5 sec.

With 150K, I would replace it if original.

 

[meerschm]

View attachment 28096

took a drive, around the neighborhood to get things up to normal operating temp

looks like 5 peaks in 15 seconds.

funny thing is, there are a couple oxygen sensor diagnostics in the emissions tests which read fine.

Guess I will order the sensor and a socket. Rock auto posted a discount someplace if I recall.

is the GM sensor recommended?

 

[gmcman]

GM is recommended. The peaks @ 5 second intervals don't tell the story though. The sensor changes voltages in steps like..... .350, .570. ,980, .245, .430, .890, etc. The changes are what you are looking at, not the peaks or valleys. Still, with that mileage I would surely change it but if it's popping out values @ 2 per second then it could be good, just catch-22 at that mileage.

 

[SEMIJim]

What's the difference between winter and summer gas anyway?

Why is summer fuel more expensive than winter fuel?

Jim

 

[meerschm]

so five cycles in 15 seconds is 3 seconds per cycle or 1.3 Hz.

thought the sign of lazy sensor is slow cycles, over 1 Hz.

I found some posts by Roadie and discussion of some scope traces, but my google foo is getting weak. (need breakfast and a walk)

http://gmtnation.com/f25/p1133-upstream-o2-sensor-diagnostics-4723/ (google worked better than the site search function)

 

[meerschm]

Why is summer fuel more expensive than winter fuel?

Jim

HowStuffWorks "Why is summer fuel more expensive than winter fuel?"

looks like the price of oil will mitigate some of the cost increase this summer.

Drivers Can Expect Break On Summer Gas Prices - WSJ.com

 

[DenaliHD66]

Good stuff. My o2 is rusted in there, and I may have a crack in my manifold so just going to replace them together (soon.......)

 

[signalnc]

my gas mileage dropped the past 2 weeks. It went from 13.8 avg to 12.4 avg. I replaced the 2 month old bosch o2 sensor with a delco a few weeks ago. Not sure if if that's the culprit or not. I might stick the bosch back on and see. The weather warmed up too, so maybe running the a/c hasn't helped either.

 

[meerschm]

View attachment 28098

The test here looks like the critical measures are rise time and fall time.

(as well as the fact that the sensor transitions from indicating too rich to too lean)



Service manual does a nice job explaining the codes related to the Heated O2 Sensor (HO2S)
codes are listed for no toggle, too slow rise time, too slow fall time, stays in the middle, or if sensor heater current is out of range.

looks like the reading above is from a stored diagnostic run once per ignition cycle, after the temps come up to speed.

 

[DenaliHD66]

my gas mileage dropped the past 2 weeks. It went from 13.8 avg to 12.4 avg. I replaced the 2 month old bosch o2 sensor with a delco a few weeks ago. Not sure if if that's the culprit or not. I might stick the bosch back on and see. The weather warmed up too, so maybe running the a/c hasn't helped either.

I wouldn't use anything Bosch on our trucks... they are junk in my opinion and I've heard nothing but horrible compatibility issues. I'd clean everything up, run some cleaner through the gas tank, and give it a few more fillups for the ECU to adjust to the changes. I ran a bunch of cleaners through about 5-6 weeks ago, and ever since then, each time I fill up it was getting better and better mileage.

 

[meerschm]

http://www.bosch.com.au/content/language1/downloads/Section_A.pdf

turns out they do know a few things about how these things work.


not saying that Bosch parts would work better than or as good as Delco, but I found the pdf interesting reading.

 

[DenaliHD66]

Well I've heard nothing but bad things about them, including not being very compatible with our trucks. Spark plugs in particular.

 

[CaptainXL]

What's the difference between winter and summer gas anyway?

Butane is added to the winter blend fuel to increase evaporation and help with starting. It is generally thought to be not as pure as summer gas, which is costlier.

The ethanol in the gas will absorb any moisture in the gas or tank. No gas tank additives such as IsoHeat should be needed nowadays.

http://www.popularmechanics.com/car...-blend-gasoline-whats-the-difference-13747431