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Unread 02-04-2002, 09:51 PM   #1
Bob K
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Join Date: Nov 2001
Location: New Bedford, MA
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??? Vacuum routing question ???

Don't even ask me to describe all the things I've removed and modified under the hood of my '87 YJ with the 258 I6. I can't even remember how it all evolved to the point it is at today. My one question is this:

If I were to run only one vacuum line to my distributor, no others spliced in, where is the best place to attach the vacuum line to? Manifold, carb, ported, unported?

I am presently still using the vacuum swithches up on the firewall above the valve cover in the distributor vacuum advance system. I don't understand exactly why, but the vacuum often holds in the line for several seconds up to over a minute until it releases and allows the idle to drop back down to where it should be.


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'87 Wrangler YJ 4.2 I6 (sorry, sold)
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Unread 02-04-2002, 11:19 PM   #2
Mudpig
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Join Date: Feb 2002
Location: north of you
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I don't know what all the other vacuum lines do but you should run advance from ported vacuum on the carb.
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It's a jeep thing, I do understand!! 89 YJ Laredo,4.2L carburated. Chrome bumpers and grill. 31 AT's on 9x15 chrome modulars. Mustang GT buckets. 3" body lift and 1 1/2" shackle lift. Completely emission & computer free. Runs great!! Took the shackle lift out, they suck!!
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Unread 02-05-2002, 06:07 AM   #3
Bob K
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Location: New Bedford, MA
Posts: 987
Is the ported vacuum the one on the right center of the carb? In diagrams it appears to be the one near the EGR valve.
__________________
'87 Wrangler YJ 4.2 I6 (sorry, sold)
JuiceBox ignition
2 1/2" ProComp Lift
31" BFG A/T's
K&N Filter
Custom Rock Guards
Turbo Muffler
Rear Track Bar in the shed
Other Tricks I won't tell to just anybody!

'99 Grand Cherokee 4.7 V8
Towing Package
K&N FIPK
ProComp MX6 shocks
Borla Exhaust
Tow Hooks
Alpine CD with Infinity+iPod connect
Just getting started!

If you're not living on the edge...
you're taking up too much space.
Bob K is offline   Reply With Quote Quick reply to this message
Unread 02-28-2002, 07:28 AM   #4
stilllearning6
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1988 YJ Wrangler 
 
Join Date: Jan 2001
Location: Norwalk, Connecticut
Posts: 70
Bob K -- based upon the schematics of the 1988 YJ 258 BBD feedback carb, the vacuum hose feeding to the vac adv of distributor receives/ carries manifold vacuum , not ported vac . The manifold vacuum source can be any inlet at the base of the Carter BBD ; the base carb inlets are all manifold vacuum sources. If my memory serves me correctly , the one that is OEM setup comes off the brass fitting near the EGR . The 2 fittings bolted to the firewall, called the " Vacuum Switch Assembly " , are the "green 10 inch manifold vac switch" and the "white 4 inch ported vac switch" . They switch " open / closed" and can feed juice back to the MCU based upon engine load : that is based upon the change in manifold vac and ported vac. The switches of the 10/ 4 are controlled by separate vacuum hoses feeding into each of them separately . There is a black /purple delay valve coupled with a small black vacuum reservoir built in-line with one of them , that is into the " green 10 inch manifold vac switch " feed hose . The MCU receives the input from the Vacuum Switch Assembly and then does its thing . I have been unable to read a detailed explanation of exactly what the MCU will do in response to the input from the 10/4 switches . I am theorizing that either the MCU changes timing / the MCU changes air fuel mix . This has stumped the Jeep dealer mechanics . The only source of ported vac would be from the location above the throttle plates , the carb outlet half way up the carb and facing the valve cover . This ported vac source also feeds ported vac to the 4 inch vac switch on the firewall , feeds ported vac to the CTO --> TVS in air box --> EGR system , feeds the ported vac to CTO --> Charcoal Evap Canister "signal" purge inlet . Hope this applies to your rig. I do not know if you rig is same as mine .
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