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Old 07-06-2013, 01:18 PM   #1
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Help me interpret vacuum gauge! Video inside

I connected the vac gauge to the brake booster port and have these readings at operating temperature. Has anyone seen this before and know what's going on inside the 4.2??


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Old 07-06-2013, 01:39 PM   #2
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heres a chart on reading a vacuum gauge
it should be steady, not fluctuating like that. how is it acting?

How to Use and Interpret a Vacuum Gauge

look at number 7, kind of looks like yours.

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Old 07-06-2013, 01:43 PM   #3
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or maybe number 13. that says adjust mixture, I'd try that first.
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Old 07-06-2013, 01:58 PM   #4
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thought about this some more, when i had my weber my 4.2 was doing close to the same thing, maybe a little less movement, jeep ran good but needle wasn't steady. I changed intake manifold and carb, now needle is steady. my carb was about 4 years old and in need of a rebuild so that might have been it or I had a slight vacuum leak and changing gaskets fixed it, not sure which one.
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Old 07-06-2013, 03:07 PM   #5
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I am going to change the intake gasket. I have a feeling that is at least part of the problem.
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