LT1 Based Engine Tech 1993-1997 LT1/LT4 Engine Related

Map sensor voltage

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Old Feb 20, 2005 | 04:58 PM
  #1  
$hawn's Avatar
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From: Wichita, Kansas
Map sensor voltage

On my scanner the map sensor voltage with the key on, engine off is around 4.62 and with it idling with the hotcam it is around 1.05-1.07. From what I'v read with the key on, engine off it should be around 5 volts or at least 4.80, and while idling it should 1/3 of that, which would be around 1.52 from the 4.62. I'v also read while idling it should be at least 1.2-1.6. So mine looks to be slightly off, but i'm not sure if it truely is with in normal specs.
Old Feb 20, 2005 | 05:49 PM
  #2  
JDBlaze85's Avatar
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From: dallas, tx.
Re: Map sensor voltage

looks normal to me. With an aftermarket cam installed, you can throw "normal specs" out the window. As long as the idle is 1.0V - 2.0V, and at WOT, you are over 4V, you'll be fine.
Old Feb 20, 2005 | 10:55 PM
  #3  
Injuneer's Avatar
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From: Hell was full so they sent me to NJ
Re: Map sensor voltage

What was the barometric pressure when you got the 4.62V reading, and what is the altitude above sea level of Wichita? Key on/engine off votage is what the PCM sets as barometric pressure, based on the MAP sensor reading. A 4.62V signal would correspond to a standard barometric pressure at about 2,000-ft above sea level - ~27.8 "Hg or 94 kPa.

What cam you are running has no affect on the key on/engine off MAP reading. 4.0V at WOT would only be 25 "Hg or less than 85kPA.... not a very good reading against a 30" (103kPa) barometer. You need to compare WOT voltage to BAR voltage. At idle, you should see a little higher MAP with the HOT cam, and the numbers you are seeing would be normal for the stock cam.

Have you checked the voltage across the gray (+5V reference) and black (ground) wires with the harness connector disconnected? Perhaps the PCM is not providing the correct +5V reference, or possibly the harness connector is damaged.

But, if Wichita is at 2,000-ft elev., it would explain everything.
Old Feb 20, 2005 | 11:12 PM
  #4  
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From: Little Rock, AR
Re: Map sensor voltage

~1332 ft elevation at Wichita mid-continent airport.
1371 at McConnell Air Force Base
Old Feb 27, 2005 | 12:28 PM
  #5  
$hawn's Avatar
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From: Wichita, Kansas
Re: Map sensor voltage

Sorry I havent replyed back to this in awhile, but the barometric pressure was about 30.00, and yeah the elevation is about 1400 ft or so, but definitely not that close to 2000 ft. The connector is new and i'm getting 5 volts.
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