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4x4 vac lines? And other probs?

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I have a few question for you guys. I pretty much am a beginner in the Jeep repair field so be gentle. I have an 89 Wrangler with a 4.2 and upgraded to Howell TBI. First for some reason my 4x4 does not work, upon examination I found that the blue line is cut and plugged. I do not know if this is the line for the 4x4 or not but I also see 2 yellow lines as well wich seem to be connected. Does anyone know of a diagram of the vac lines. I also have a problem with high idle around 1500 to start then 1000 after about 15-20 seconds. I have noticed a high pitched whistle like a vac leak however when I take off one of the plugs on the TBI the whistle goes away. You guys have any ideas? I am pretty much stumped. Any help would be appreciated.

Thanks in advance,

98 Cherokee Sport
89 YJ Laredo
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well am not all a wrangler expert.. but i do know they have some sort of vacuum line going to the front diff., i think.. and it needs to be hooked in order to engage 4 wheel drive.. as for that howel thing.. mmm.. nada.. dont have the cash for one.. so i dont have any experience with it..

survival is instinct, but living takes guts
When I had this problem with my old '88 YJ, I could never find a diagram for these vacuum lines. I seem to recall that one of the lines was plugged on mine too. They go back to the top of the tranny ( I think) where they plug into a switch. You can start troubleshooting at the front axle. The shift motor on the passenger side of the front axle should have vacuum when 4wd is engaged. Once the shift fork in the axle engages, the vacuum goes up to a vacuum switch mounted on the firewall next to the battery. The vacuum there will apply a ground to the 4wd indicator on the dash and it should light up. In the course of its travel, the vacuum goes through some of those "one way" valves.

My troubleshooting turned up multiple problems... bad lines... a one way valve that was backwards... and a bad bulb socket on the dash. I read about a lot of guys that had a bad switch on the tranny too... So start at the axle to see if the vacuum gets there...then you can troubleshoot forward or backward from there. I hope this helps...

79 CJ7 Golden Eagle, 304

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i too have a simailar 87yj 4.2 and this site proved most valuable. run yourself a hard copy and keep in your shop. emissions, vacuum, carb, timing it has it all.
good luck
Thanks for the help guys I will take a look into the things you mentioned.


98 XJ Cherokee Sport
89 YJ Wrangler Laredo
Hi Guys, I'm selling a manual disconnect system for CAD front axles on Jeeps that does away with the
vacuum system altogether and the associated problems. E-mail me for more info.
[email protected]
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