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Topic Review (Newest First)
01-16-2011 02:23 AM
90YJinPC That is a vacuum resivor under the battery. Looks like it has been disconnected by your photo. Here is a site that may help answer some questions.

Table of Contents

More info that may help.

To move the fork, Chrysler decided to use a vacuum powered motor. A vacuum source line is run from somewhere on the engine (the location varies and can come from the brake booster, the manifold, etc) to a vacuum switch on the transfer case. When 4wd is selected, the switch sends the vacuum along several lines to the shift motor located on the front axle. The vacuum pressure is applied to a diaphragm inside the motor, thus sucking it one way or the other, depending on whether the axle is engaging or disengaging. The diaphragm is connected to the end of the shaft that the shift fork is attached to, thus moving the fork along with it. The problem with this system generally lies in the vacuum lines themselves. Over time, the lines harden and crack and dry rot. The older the vehicle, the more likely this will happen. As cracks form, air leaks soon follow, lowering the amount of vacuum pressure that is in the lines. After a certain point, there is no longer enough pressure to move the diaphragm, thus causing leaving the fork motionless. More often then not this is problem with the system. Included below is a diagram of the 4wd vacuum system.
01-15-2011 08:38 PM
Update 1-15-2011

Ok, today
1. Finished the wiring side of the Nutter Bypass and cleaned up harness real good.

2. Ripped out all the vacuum lines and used the above diagram keeping the canister.

Result = It starts a little easier but runs like crap same as before.

Concerns =

1. I have no vac lines from carb going or manifold going to 4x4 system.

2. There is a round ball looking object with 2 vac lines running out of it under the battery tray what is this? Can I rip it out?

3. I know I have to set the timing but I've never done it before.
01-11-2011 01:48 AM
90YJinPC Sound like your carb. idle ports are plugged. Very common with stock carbs. The white smoke is a concern. Check your water and oil and make sure there is no mix between the two.
01-10-2011 10:28 AM
b.rainey01 Thank you Fweaky. I'm trying to see what all I can rip out of this thing now. there is a rat nest of vac lines. I replaced all of them with new lines. But, I'm dying to finish the Nutter and clean house under the hood.
01-10-2011 04:36 AM
Fweaky Tie the 4wd vacuum line into the manifold vacuum like the top picture.
01-10-2011 04:04 AM

I'm working on both posts. I have started the Nutter Bypass. I only have the purple to purp and orange to orange and back in the loom. I need a good diagram on the vacuum lines post nutter. I've seen a few diagrams, one of them shows a line to the 4wd system off the manifold vac. Is this correct? Here is a pic of the one I found to be the best one so far. Which one of the two should I use for my 88 YJ 4.2 L I6 with carter bbd?
12-02-2010 10:54 AM
Thank you for the response very much

I have not been able to try your suggestions yet. But, I will this weekend and let you know how it went. Again, thank you very much... If that works I owe you big time!
12-01-2010 08:57 PM
drox welcome to the fourm you might want to try a nutter bypass
12-01-2010 04:49 PM
mholloway1809 Set the engine to the top dead center mark on the crankshaft and check the postion on the #1 spark plug wire, If its off by half rotate the engine 1 more revolution and check that the number one plug wire is in the correct position.
then with the distributor cap removed turn the engine over and verify which way the rotor turns and insure the plug wires are connected in the proper order in the correct direction.
Then start the engine and check and adjust the ingnition timing as needed, remember to remove the vac hose from the distributor before checking.
11-29-2010 10:20 AM
1988 YJ 4.2L I6 Very rough idle and no power

It had sat up for 8 years in our shop. Put all the new parts on and got it running. It ran smoked but had great response with no hesitation. It sounded great except for a little spuddering like the plugs needed replaced. Then it got hard to start and would run real rough. Part of it may be that the vac lines aren't all correct. The diagrams I've found mostly suck or they are missing lines that I have.
It's the 4.2 I6 factory air cleaner with K&N filter runs like crap with the filter on or off.

Forgot to mention i replaced the rotor button also.
11-28-2010 09:21 PM
mholloway1809 How did it run before working on it ?
11-28-2010 09:55 AM
yjforlife check your timing if its off at all then it does that
11-28-2010 03:42 AM
1988 YJ 4.2L I6 Very rough idle and no power

I have replaced all the lines after my dad removed them all. I probably dont have them in the correct locations. Need a diagram very bad.
When it starts it will idle but very rough and smokes pretty bad white smoke. when you press the eccelerator it is very sluggish.

Has new accel plug wires 7mm, new distrib cap, new plugs, new vac lines, k&n filter, Flowmaster, new alt, new radiator, new belts, new control module, new batt, new starter.

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