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dakota49
Dodge Dakota
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2/21/2008
01:14:16
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 Subject: RE: TYPICAL VACUUM READING
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Message:
My Dak is an 88 and I am getting 20-21 inches of vacuum at idle, mine idles at about 1000 RPM though. You should have more than 10-11 at idle, I am thinking maybe the timing chain has jumped time and your valve timing is slow, that could cause the low vacuum readings, then so could a blocked cat/muffler/exhaust system.
Good Luck
Dakota49
1988 3.9 4X4 5speed
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pete
Dodge Dakota
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2/21/2008
11:31:09
| RE: TYPICAL VACUUM READING
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Message:
dakota49,what iam experiencing on my scan tool is showing 34KpA or 10 inches of vacuum not engine itself which is 17 inches of vacuum and same goes for every full vacuum port i connect to including the MAP Sensor port my concern is why is this MAP Sensor reading LOW vacuum at idle as shown on my scan tool and iam not getting any faults stored or MIL lamp on just in my understanding of this my PCM is thinking my throttle is open when its not so this leads me to my thoughts whats going on here, and don't let mt come off as a d!ckhead towards you or anyone else that is willing to help me with this.
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Behaley
Dodge Dakota
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1/31/2010
20:33:26
| RE: TYPICAL VACUUM READING
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Message:
I know this is an old post, but I might have your answer. I haven't had a chance to verify this, but I think MAP stands for Manifold Absolute Pressure, not Manifold Air Pressure, and measures opposite of a vacuum gauge. What that means is that it reads zero for a perfect vacuum and actual air pressure or barometric pressure with the engine off. You said that you read 28 in hg with the engine off and 10-11 inhg with the engine running at idle. You also said that a vacuum gauge read 17in hg at idle when hooked to the intake manifold. The vacuum gauge reads zero in hg when open to the atmosphere. So, in short 28-17=11inhg. Your MAP is working correctly.
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