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  #31  
Old November 17th, 2019, 15:17
lawsoncl lawsoncl is offline
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Re: Low idle while coming to complete stop?

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Originally Posted by MickeyS View Post
Well my vacuum at the manifold is fluctuating pretty good. I don't have any reason to think the gauge is broken but I borrowed it from a friend who had never used it.

https://youtu.be/gnb12BEDUfI

Low and erratic, web search seems to diagnose valve springs. I will try to get ahold of another gauge to do a dummy check.

The bouncing needle is perfectly normal. Some gauges have a small valve to dampen the oscillations of the needle. The amount of vacuum at idle doesn't seem that low to me.
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  #32  
Old November 17th, 2019, 15:20
MickeyS MickeyS is offline
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Re: Low idle while coming to complete stop?

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Fuel pressure is a perfect 49

another view of a plug with what looks like oil on the threads. it does read as oil on paper towel. I don't seem to be visibly burning any or missing much oil from the crankcase, not sure if this is from a previous leaking valve cover or what.

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Originally Posted by lawsoncl View Post
The bouncing needle is perfectly normal. Some gauges have a small valve to dampen the oscillations of the needle. The amount of vacuum at idle doesn't seem that low to me.
thanks. if so, that's great news. everything I'm reading on youtube university and academy of google says this is abnormal, to not have a solid needle.
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  #33  
Old November 17th, 2019, 16:57
MickeyS MickeyS is offline
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Re: Low idle while coming to complete stop?

https://www.youtube.com/watch?v=vh3Z-F6KGkI

I watched this video and the wobbling needle on the gauge later still looks a lot better than mine.
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  #34  
Old November 17th, 2019, 17:48
lawsoncl lawsoncl is offline
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Re: Low idle while coming to complete stop?

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Originally Posted by MickeyS View Post
https://www.youtube.com/watch?v=vh3Z-F6KGkI

I watched this video and the wobbling needle on the gauge later still looks a lot better than mine.
In the video, he's using a gauge meant for checking engine vacuum that has some dampening. The dampening is typically added by a restricted line, a weighted needle, or oil in the gauge. You're using the gauge on a mity vac hand pump which has no dampening so you're going to see the pulsing more pronounced at idle as each cylinder pulls on the intake stroke. If the needle is consistently dropping a lot once per rev rather than bouncing around at 6x the revs, then I'd suspect maybe a problem with one cylinder and then do a compression test which would be much more revealing. Even slowed down to 1/4-speed, I don't see more the needle wagging more than a few psi.

The gauge set I use to sync motorcycle carbs measures each cylinder separately and you can really see the oscillations on each piston stroke. This gauge set has valves on the vacuum line you choke down to get a reading steady enough to balance the carbs.
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  #35  
Old November 17th, 2019, 19:36
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cruiser54 cruiser54 is offline
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Re: Low idle while coming to complete stop?

Okay. Spray carb cleaner around the intake manifold and see if there's a vacuum leak around #6.
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  #36  
Old November 17th, 2019, 21:23
MickeyS MickeyS is offline
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Re: Low idle while coming to complete stop?

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Originally Posted by lawsoncl View Post
In the video, he's using a gauge meant for checking engine vacuum that has some dampening. The dampening is typically added by a restricted line, a weighted needle, or oil in the gauge. You're using the gauge on a mity vac hand pump which has no dampening so you're going to see the pulsing more pronounced at idle as each cylinder pulls on the intake stroke. If the needle is consistently dropping a lot once per rev rather than bouncing around at 6x the revs, then I'd suspect maybe a problem with one cylinder and then do a compression test which would be much more revealing. Even slowed down to 1/4-speed, I don't see more the needle wagging more than a few psi.

The gauge set I use to sync motorcycle carbs measures each cylinder separately and you can really see the oscillations on each piston stroke. This gauge set has valves on the vacuum line you choke down to get a reading steady enough to balance the carbs.
thanks for taking me to school. I'm going to get a stand alone vacuum gauge from HF to do a dummy test, then get a buddy to help me with the compression test soon. Will also spray around cylinders at manifold (again) as mentioned above, but I had done this a while back.
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  #37  
Old December 3rd, 2019, 19:15
MickeyS MickeyS is offline
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Re: Low idle while coming to complete stop?

Lawson was totally right. Threw a HF vacuum gauge on the manifold and pull a solid 18 in hg at hot idle with the gauge only instrument. I passed smog today which is good news, if I didn't pass I was going to stop throwing time and money at the issue but the jeep passed with colors, so with perfectly strong vacuum and clean emissions I can start doing more work to get to the bottom of this.
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