Is my MAP sensor going bad ?
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Race Director
Joined: Dec 1999
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From: Forked River NJ
Is my MAP sensor going bad ?
Manifold vacuum is at 8 to 9 inches. I have an EZ efi 2.0 and looking at the master screen while idling it is showing around 68-70. Jumping a little but so does the 8-9 inches I am getting on my vacuum gauge. Now I am running a pretty healthy cam so the 8-9 is about right but why is the computer showing 68-70. That converted is about 20 inches. The car all of a sudden started cruising very poorly. Low speed 1500 to 2300 rpm is not good at all. WOT the car runs good but could probably run better.
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Manifold vacuum is at 8 to 9 inches. I have an EZ efi 2.0 and looking at the master screen while idling it is showing around 68-70. Jumping a little but so does the 8-9 inches I am getting on my vacuum gauge. Now I am running a pretty healthy cam so the 8-9 is about right but why is the computer showing 68-70. That converted is about 20 inches. The car all of a sudden started cruising very poorly. Low speed 1500 to 2300 rpm is not good at all. WOT the car runs good but could probably run better.
The MAP reading looks correct to me. A vacuum reading of 8-9" Hg means that the manifold is only about 1/3-1/4 depleted of normal air pressure (Full depletion would be 30" Hg). IOW, the manifold at 8-9" Hg is 2/3 to 3/4 full of normal air pressure (14.7 psia). Full manifold air pressure (14.7 psia) as read by a MAP sensor is IIRC 105 kiloPascals. Take 2/3 to 3/4 of 105 kPa and you get about 68-70 kPa.
Again, I invite corrections if I'm thinking wrong this evening.
Last edited by 69427; Oct 6, 2017 at 08:23 PM. Reason: Grammar correction. Long day.
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From: Plano TX
^^^^ Yes, that is correct.
Assuming sea level, 0" of vacuum is a map reading of a little over 100. Perfect vacuum will be a map reading of 0.
The higher the altitude the lower the 0" vacuum reading will be.
Assuming sea level, 0" of vacuum is a map reading of a little over 100. Perfect vacuum will be a map reading of 0.
The higher the altitude the lower the 0" vacuum reading will be.
Thread Starter
Race Director
Joined: Dec 1999
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From: Forked River NJ
It's been a long frustrating day, so I welcome any corrections if my thinking is foggy this evening.
The MAP reading looks correct to me. A vacuum reading of 8-9" Hg means that the manifold is only about 1/3-1/4 depleted of normal air pressure (Full depletion would be 30" Hg). IOW, the manifold at 8-9" Hg is 2/3 to 3/4 full of normal air pressure (14.7 psia). Full manifold air pressure (14.7 psia) as read by a MAP sensor is IIRC 105 kiloPascals. Take 2/3 to 3/4 of 105 kPa and you get about 68-70 kPa.
Again, I invite corrections if I'm thinking wrong this evening.
The MAP reading looks correct to me. A vacuum reading of 8-9" Hg means that the manifold is only about 1/3-1/4 depleted of normal air pressure (Full depletion would be 30" Hg). IOW, the manifold at 8-9" Hg is 2/3 to 3/4 full of normal air pressure (14.7 psia). Full manifold air pressure (14.7 psia) as read by a MAP sensor is IIRC 105 kiloPascals. Take 2/3 to 3/4 of 105 kPa and you get about 68-70 kPa.
Again, I invite corrections if I'm thinking wrong this evening.
Thread Starter
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
I was having one of those days yesterday where my brain was not thinking. I was bassackwards yesterday. Thinking 0 kpa. Was atmospheric pressure on the map. Went out this morning and just turned the ignition on and the sensor reads 105kpa. So it seems to be working correctly. I'll have to look elsewhere for the rough running.
