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post #1 of (permalink) Old 02-01-2001, 12:54 PM
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Sol-vac Idle Problem

I'm trying to understand the operation of the devices on my first Jeep that I purchased six months ago. One of those devices is the Sol-vac.

It seems the vacuum portion of my Sol-vac likes to kick the idle up for a few seconds, release, then reapply, setting up a really nasty idle oscillation. Does anyone else have this problem or have any ideas as to the cause?

1986 CJ-7, 258, T-5, Stock
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post #2 of (permalink) Old 02-01-2001, 01:00 PM
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Re: Sol-vac Idle Problem

This site should help you out...

Tommy B. in AZ -
More Guts than Brains.
[img]/wwwthreads_images/icons/tongue.gif[/img] WHASSSUP!?!?!?!?
post #3 of (permalink) Old 02-01-2001, 02:58 PM
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post #4 of (permalink) Old 02-01-2001, 03:00 PM
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Re: Sol-vac Idle Problem

Thanks. Unfortunately I had already referenced that site previous to my post. It appears that the computer is commanding the vacuum portion on and off after the initial startup profile shown on that site.

It seems that this tends to occur more frequently as soon as the computer goes into closed-loop mode (after coolant sensor indicates warm). I know the computer will command this device on at other times, but I was hoping someone would have seen this behavior before or would know what causes this idle oscillation.

1986 CJ-7, 258, T-5, Stock
post #5 of (permalink) Old 02-01-2001, 08:08 PM
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Re: Sol-vac Idle Problem

I have the same problem occaisionally on my 90 YJ. I haven't resolved it yet, but here's what I've got so far. (I'm putting a major disclaimer on this post because it's been a while since I worked on this and can't locate all the information I had, so it's mostly from memory).

It's my understanding that one of the vacuum switches (4 or 10, don't remember which) indicates a deceleration mode to the computer, which causes the computer to step up the idle to reduce emmissions. I think that as soon as the computer goes to closed loop, due to low idle speed and a marginal vacuun switch, the computer detects deceleration and kicks the idle up. It's held there for about 5 seconds and released. As soon as it's released, the idle goes down which triggers the switch again. I was able to test this theory one time by disconnecting the vacuum switch while the problem was occuring and the problem went away.

I think that the vacuun switch does not funtion correctly when it is cold, when the underhood temperature gets warm enough the switch starts functioning correctly and the condition goes away. This would also explain why when it is really cold, it will stay on fast idle for the whole 20 min ride to work.

Since this isn't my daily driver, I haven't been in a big hurry to verify my theory. Let me know if you find out anything different with yours.


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post #6 of (permalink) Old 02-02-2001, 11:30 AM
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Re: Sol-vac Idle Problem

Thanks for the information Jerry. That sounds exactly like what's going on. Now with your information, I'll see if I can get a better diagnosis of this oscillation. Of course, I need to finish with my TR TFI upgrade first and get everything back together again... [img]/wwwthreads_images/icons/crazy.gif[/img]

The 10" (green) switch is hooked up to manifold vacuum and is only open when manifold vacuum exceeds 10". The 4" (white/tan) only closes when ported vacuum exceeds 4". I'll have to do some RPM vs. vacuum levels on both manifold and ported sources to see what I'm up against.

<font color=blue>1986 CJ-7, 258, T-5, Stock
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post #7 of (permalink) Old 02-02-2001, 11:38 AM
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Re: Sol-vac Idle Problem

Off-Road's BBD diagnostics is a great page, and gives a good understanding of how that infernal system is 'sposta' work. However, we all know it don't work that way. I'm a firm believer in two heads are better than one, and two refrence manuals are better than one. Have you looked at:


This also is a great diagnostic and explination of the system from another view. Hope it helps.

Safe Jeepin'

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