MAP sensor issue find in my '11 5.3 Tahoe

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Jul 16, 2005
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Montague, NJ
My hwy mileage dropped to 16.3 from 19 so I had to look into it. Autoenginuity scan tool, no codes set in any of the 4 code families.
Scan tool has a MAP test function, tests 1 and 2. It failed test 1 yet no codes current or pending.
Replaced MAP (OEM replacement) and mpg came back to 19 hwy. on a 250 mile test run.
In my diagnosing I saw the real time mpg bouncing around on decel. from 99 mpg to down in the fifties and back up all over the place with foot off the gas. Zero drivability issues also.
Just sharing incase someone else runs into this.
 
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Just wondering, but did you hand calculate your mileage when all of this was going on?
 

repairman54

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Autoenginuity's PC based program. And I need to add when the scan tools MAP test was left running in real time mode it would pass, then fail, then pass again over a 5 min. span. Sensor was intermittent enough to fail test but not set a code.
What scan tool was this?
 
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Been trying to pinpoint the drop in fuel economy on my yukon, may check my map sensor to verify it is good.
 

repairman54

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Been trying to pinpoint the drop in fuel economy on my yukon, may check my map sensor to verify it is good.
For me it started when I cleaned my MAF sensor as part of a ''maintenance ritual'', had not been done in over 50k miles. Only paper air filters also. MPG dropped after cleaning it. MPG is supposed to improve with a clean MAF. Changed MAF with OEM replacement and no improvement and that started the search for the lost mpg's and finding the bad MAP.
125k miles on the truck.
 
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For me it started when I cleaned my MAF sensor as part of a ''maintenance ritual'', had not been done in over 50k miles. Only paper air filters also. MPG dropped after cleaning it. MPG is supposed to improve with a clean MAF. Changed MAF with OEM replacement and no improvement and that started the search for the lost mpg's and finding the bad MAP.
125k miles on the truck.
My decel mpg never really got above 50. Swapped in a used sensor from my other vehicle and on the way to work this morning my decel mpg would go to 99. Avg according to tank was up 3 mpg. Hopefully a tank average will confirm results. My old map sensor had quite a bit of carbon in it.
 

repairman54

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Did a second run with my 6x6x12 cargo trailer in tow and mpg was up to 14.3 vs the 12.3 the last time I towed it with the old bad MAP sensor.
Light load in both cases. Darn partially failed MAP sensor has been a issue for a while now and more important now that fuel is up 50%.
I'm not a parts swapper as a retired tech who needs proof of failure but that MAP sensor is a candidate if all else fails in my book now.
 

yst

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Aug 26, 2014
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New Jersey
Did a second run with my 6x6x12 cargo trailer in tow and mpg was up to 14.3 vs the 12.3 the last time I towed it with the old bad MAP sensor.
Light load in both cases. Darn partially failed MAP sensor has been a issue for a while now and more important now that fuel is up 50%.
I'm not a parts swapper as a retired tech who needs proof of failure but that MAP sensor is a candidate if all else fails in my book now.
Proof of failing for MAP sensor is reading the pressure data at non running engine and comparing this data with actual atmospheric pressure at your location.
Deciding about pressure sensor condition by MPG is not correct.
 

repairman54

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Proof of failing for MAP sensor is reading the pressure data at non running engine and comparing this data with actual atmospheric pressure at your location.
Deciding about pressure sensor condition by MPG is not correct.
MAP passed that test. Only reason I changed it was my scan tool has 2 tests for the sensor and one of the tests would swing pass to fail and back to pass. Observing instant mpg not going into the 90's on a long 55mph decel. was another tip off of a intermittent sensor.
 

yst

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Aug 26, 2014
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New Jersey
MAP passed that test. Only reason I changed it was my scan tool has 2 tests for the sensor and one of the tests would swing pass to fail and back to pass. Observing instant mpg not going into the 90's on a long 55mph decel. was another tip off of a intermittent sensor.
You have two map sensors now and connecting them to hand vacuum pumps and creating the same level of vacuum you should observe the same signal on the scan tool if both is good. Do it at few points and compare data.

Edit: Pay attention to the rubber o-ring, Honda advised to replace o-ring every time you removed the MAP sensor.

Also, you can observe the actual pressure by the scanner when you rolling down the mountain in Montague.
 
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repairman54

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New MAP cured it. Comes with O ring.
I trust my scan tool, not even worth my time to play with vac. pump and sensors.
Maybe now my monitors will all fully check and pass.
 

repairman54

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Long term follow up on my MAP issues.
Highway mpg is running 19 -20 mpg via the DIC on a 450 mile round trip I regularly do year round. About 6 trips so far, so good.
DIC info is back to where it was 50k miles ago when I was ''hand checking'' it's accuracy/readings.
 
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My decel mpg never really got above 50. Swapped in a used sensor from my other vehicle and on the way to work this morning my decel mpg would go to 99. Avg according to tank was up 3 mpg. Hopefully a tank average will confirm results. My old map sensor had quite a bit of carbon in it.
GM was always fond of map sensors, in fact, the go-faster boys who added superchargers would modify the map, to make the computer provide the correct fuel trim.
 
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