MAP sensor readings and symptom diagnosis

imactj2004

imactj2004

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This ones a head-scratcher for me but hopefully someone can help. Im trying to understand how to interpret MAP (inHG) readings on my scanner.

Context is this:
according to FSM, one of the conditions required for the Jeep to run the EVA drive cycle is to have MAP(inHg) of 22 or higher. So….

Q1: is that with engine off, at idle, or driving?

Q2: If my scanner shows a value below 22, then how can I diagnose the cause? Seems to me that the cause could be anywhere within the EVAP system as a whole or it could be the actual MAP sensor itself…right?

My first instinct is to replace the sensor but that seems futile if the sensor isnt the problem. I’m not getting any codes but I do have the flashing EVA alert, and havent been able to complete the drive cycle despite going through several tanks of gas and attempting the “idle five min the drive 35-40 for ten min” condtions at least 10 times now.
 
MAP sensor should read ambient pressure with the key on, engine off.

If you floor it, MAP should read approx. ambient, which will be over 22 in hg pressure.

Idle MAP reading is going to be around 10 in hg pressure.

If your scanner is converting it to a vacuum reading, then you will have to subract that from the ambient to get a pressure reading.
 
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JKP said:
MAP sensor should read ambient pressure with the key on, engine off.

If you floor it, MAP should read approx. ambient, which will be over 22 in hg pressure.

Idle MAP reading is going to be around 10 in hg pressure.

If your scanner is converting it to a vacuum reading, then you will have to subract that from the ambient to get a pressure reading.
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thx for clarifying

ok, well, then everything is “fine” for my system. Not quite sure why I cant get the drive cycle to work.
 
Last edited:
I can't think of a reason, the 05 and 06 have a recall for that issue, but I see you have an 04 and the recall doesn't apply to it.
 
JKP said:
I can't think of a reason, the 05 and 06 have a recall for that issue, but I see you have an 04 and the recall doesn't apply to it.
Click to expand...

hmmm. my father n law frankensteined a salvaged ‘04. Suppose I’m S.O.L. if he pulled parts from an 05.
 
The 05 and 06 have different cam sensor tone wheel, different crank sensor tone wheel, different PCM. So not likely unless he pulled entire engine with PCM.
 
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imactj2004 said:
This ones a head-scratcher for me but hopefully someone can help. Im trying to understand how to interpret MAP (inHG) readings on my scanner.

Context is this:
according to FSM, one of the conditions required for the Jeep to run the EVA drive cycle is to have MAP(inHg) of 22 or higher. So….

Q1: is that with engine off, at idle, or driving?

Q2: If my scanner shows a value below 22, then how can I diagnose the cause? Seems to me that the cause could be anywhere within the EVAP system as a whole or it could be the actual MAP sensor itself…right?

My first instinct is to replace the sensor but that seems futile if the sensor isnt the problem. I’m not getting any codes but I do have the flashing EVA alert, and havent been able to complete the drive cycle despite going through several tanks of gas and attempting the “idle five min the drive 35-40 for ten min” condtions at least 10 times now.
Click to expand...

Did you solve your problem? If not I maybe able to help. PM me.
 
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