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Discussion Starter #1
I have had intermittent issues with my Maf sensor for some time, only in higher elevations and just replaced it.
After replacement took a test drive, and noticed a decrease is mpg.
My truck is chipped with duramileage and get about 24 to 27 mpg unloaded highway miles for years. After replacing the Maf sensor, now getting 20 to 22 mpg during the test.
Why is a brand new Maf sensor causing such a huge issue with MPG?
My mechanic informed me that the ecm would recalibrate with the new sensor after driving a few miles. The test drive was approximately 40 highway miles.
Also noticed that my temps have increase during the test drive as well. Guessing that is related to the sensor not being calibrated properly and causing the engine to run less efficient. Upper and lower radiator hoses were replaced last week and new coolant added. So my cooling system is not the issue.
Any thoughts would be appreciated.
 

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Welcome to DieselPlace

Please tell us more about your truck ( Year, Make, and Model) and list any known mods
 

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Discussion Starter #3
Welcome to DieselPlace

Please tell us more about your truck ( Year, Make, and Model) and list any known mods
2005 Silverado 2500 hd, 6.6 Duramax LLY.
Have duramileage programmed for economy mode. Otherwise completely stock.
Has a new air and fuel filters.
Other maintenance also performed.
Everything was normal until I installed the new maf sensor.
 

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You really get that kind of mileage? My 04 lly gets 17 unloade new and still does today and I drive like the old man that I am!
 

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Discussion Starter #5
I certainly do get that range of mileage after using the duramilage programmer.
Best i've even gotten was 27 mpg round trip from San Diego to Los Angeles. Not loaded.
Just returned from a 3500 road trip and clocked 24 mpg for the entire trip.
I drive between 65 and 70 mph on the freeway using cruise control.
I'm the one everybody passes on the freeway.
 

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I certainly do get that range of mileage after using the duramilage programmer.
Best i've even gotten was 27 mpg round trip from San Diego to Los Angeles. Not loaded.
Just returned from a 3500 road trip and clocked 24 mpg for the entire trip.
I drive between 65 and 70 mph on the freeway using cruise control.
I'm the one everybody passes on the freeway.
When you replaced your MAF did you use an OEM replacement part or aftermarket ?
 

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Discussion Starter #7
Aftermarket. Pulled out an Hitachi and replaced with Hitachi.
Part number was looked up on rockauto but ordered through Amazon because it was cheaper.
 

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Aftermarket. Pulled out an Hitachi and replaced with Hitachi.
Part number was looked up on rockauto but ordered through Amazon because it was cheaper.
You may have gotten a China clone part. I would recommend replacing with a GM OEM or AC/Delco part only.
 
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Discussion Starter #9
That's entirely possible.
Any comments regarding the mechanic saying that a drive would be required for the ecm to calibrate with the new SENSOR? I would think that 40 miles should be plenty for it to do whatever it needs to do.
 

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The ECM produces a 5V reference supply (power) that goes to the MAF, and also a low reference (ground). The MAF returns the calculated signal back to the ECM. If the MAF sensor is sending the correct information, there is nothing for the ECM to do except to operate with the new (hopefully correct) information. There is no calibration involved.

When you mention a difference in altitude, I think of the MAP sensor, which measures the pressure (boost or vacuum) that is being fed into the engine.

It might be helpful to let us know what your MAF reading is at idle in park. Should be in the mid to upper 30's measured in gm/sec. Also, if you can read the MAP and BARO, please tell us what those readings are key on, engine off in in/hg. Those readings will vary with altitude.

Have you tried putting your old MAF back in? If so, did your good mileage return?
 

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Discussion Starter #11
You seem very knowledgeable. Unfortunately I have no idea how to measure what you are asking. I'm not a mechanic and do not have any specialty tools for such measurements.
I will provide an explanation of the issue with the old Maf.
I live in San Diego and regularly travel to Yuma Arizona. The only time the Maf sensor throws a code in when I stop in the local mountains (4000`), seems to only happen there. Have been in other locations at higher elevations without any issues. Just strange. Indian casino voodoo.
It's not a hard code triggered since it will eventually reset itself and I do not notice any difference in power or mileage. It has triggered a turbo under powered code on occation as well.
Just getting tired of seeing it so decided to replace it.
I do have the old sensor and can reinstall it, and I'm sure everything will be back to normal.
I was just hoping to find a solution with the new sensor.
Of course the new sensor could be defective. That happens.
 

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Discussion Starter #12
The new sensor is not throwing any codes.
I do notice a lack of power and my mpg gauge will drop rapidly while idle at a stop light. That's new.
 

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Remember that all electrical devices need supporting circuitry. If that circuitry isn't properly functioning (short to power, short to ground, open), then you will have problems.

Stop by an O'Reilly Auto Parts store and ask them to help you figure out what your problem might be by scanning for those 3 readings I previously listed. O'Reilly stores have very nice, very capable Bosch scanners and they do this for free.
 

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Discussion Starter #14
Good advice. Was not aware of that. Thank you.
 

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You really get that kind of mileage? My 04 lly gets 17 unloade new and still does today and I drive like the old man that I am!
Yea, us too. I've read claims over the years of some really high MPG, but have never seen it personally. A buddy with a nearly identical truck used to tell me he got 21mpg. Then, we did a 5500 mile test drive with both our trucks. Hand calculated. He got on average 1mpg better than me. I averaged 18mpg over a mostly highway 5500 mile trip. As bad as 15 and as good as I think 21, iirc. But average overall was 18. And wind resistance was the number one factor followed by speed. Those are connected however as with increased speed the drag from wind resistance goes up exponentially. Air density matters also as I went from nearly sea level to the continental divide and back. And saw the difference in mpg. Best mileage was flat land in Ohio at construction zone speeds.

His truck is an 06 Chevy 2500 LBZ crew cab, short bed 4x4 with over 130,000 miles. Mine, an 06 GMC 2500 LBZ extended cab, long bed 4x4 w/ a cab height camper shell with not even 70,000. We were both loaded about the same - him with a loaded bed of goods in the open air, me with a lesser load under the camper shell - and driving as a caravan for much of it so same speeds and conditions.

Since that hands on road test back in 2015 I don't even bother to check it anymore. We either have two odd trucks or all these high mpg folks do.... or they are incorrect in their observations. Is what it is. If you're at 17, you're right in there.

My buddy no longer claims he's getting 21 mpg (y)

My around town mpg is 16 with a light foot. As bad as 14 with a heavy foot.

We also switched out (and cleaned) with each other our MAF sensors to see if there would be a change, if that was the cause of his extra 1mpg. There was no difference when doing so.

Note: All was hand calculated (not the inaccurate driver readout) and checked against 2 GPS units to assure the miles and speeds driven as the speedos are not precise. Speeds never exceeding more than 5 over the posted limit. We both drive like old men. At the same exact cruising speeds, he was typically about 100 RPMs less than me, if you can believe the trucks' tachometers. Cruise set most of the time. I've owned my truck since new.
 

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The only reason I know what I get is because my low fuel light comes on at 300 miles and it only takes 17-19 gallons of fuel. I need a new sending unit,but it has been that way for about 5 years and until it completely dies I just fill up after 300 miles or low fuel light.
 

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Discussion Starter #17
Ok, here is my update.
Trucknwasnalready in the shop for differential service so had the tech take measurementsnwhilenhenhad it.
Results:
114 degrees f intake air
G/s @ idle
38.6 - 37.8 in gear
Idle Maf 1.33 - 1.35
103 gross air @ 2k rpm.

Thisnisnthe info in was given.
I did pull the new sensor out, cleaned and reinstalled the previous sensor. Same symptoms now with both.
Either my original sensor went bad and is acting likenthe new sensor, or its something else.
They are troubleshooting it now.
 

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At least at idle, your MAF reading is what I expect it should be.
 

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For what it's worth, and just throwing it out there... Efi Live showes my 2005 stock tune with Maf sensor/maps disabled. It is all Map based.
 

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Discussion Starter #20
OK i have an update for everybody.
First of all let me say thank you to everybody for your input.
After a few weeks of dealing with this issue, spending more then i wanted at the shop, and pulling my hair out, i think i finally found the issue/solution.
Let me start by mentioning that the maf sensor that was in the truck, was an Hitachi model AFH90M-01A.
I am the second owner ow this truck and have no way of knowing if this was the original or not.
I could not find that part number anywhere other then Ebay. Not going there. So i ordered the equivalent Hitachi from Amazon model #MAF0081. This did not restore my power or mileage. So i decided to by OEM (AC Delco) from Amazon. It arrived today and i installed it. Evfewn though the packaging says AC Delco, the sensor itself is labeled Hitachi. Very close model # from what i pulled out. Model AFH90M-01B. Still power not restored.
I was able to restore the power by restoring my tune back to stock, test driving, then restoring the performance tune.
Granted, i have only driven a few miles and need to take a long road trip to determine if everything is back to normal, but it seems that was the issue. I hope this info can help other having the same issue if a tuner is used.
 
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