1990 Jeep Wrangler Islander 4wd Question

For a good look at all the vacumn lines for the engine, start here:

The front axle disconnect system does not seem to be well documented. There is a black plastic line from the driver's side of the engine to the vac switch located on top of the transfercase. Then 3 lines going to the vac motor on the axle. Take a look at the vac motor on the axle, see if it still has the molded plug attached to the vac ports. With the engine running, tranny in neutral, transfer case in 2wd, CAREFULLy reach down to the front axle molded plug and see if you have slight vac on the yellow line, move it to 4wd, see if you have slight vac on green line. If no vac on either, you have a bad line going from the engine to the transfer case. If either green or yellow and doesn't switch, bad vac switch. If vac on one, no vac on the other, probably a bad vac harness.

A lot of folks will tell you to replace the vac system with a cable, not a bad option. I stuck with the vac system since I switch from 2WD to 4WD a lot.

Part numbers you may need:

vac harness (complete) 5300-2033 About $75 new at the dealer only vac switch 5300-1101

If you post a valid e-mail address, I'll send you some diagrams.

NewbieJeepGuy wrote:

This site might help you out some:

The Haynes 'CJ' manual is the best one to have for your engine and it's electrics. That book has great detail on the 258.

If all the vacuum lines are off, then the computer will have gone into 'limp home' mode clamping down on the timing and carb mix and the engine will run like a bag of dirt.

If you want to put it all back stock, see the link I posted above.

If you want to put the computer out of your misery it can be done by simply adding two new wires and hooking the orange and purple wires at the ignition module to the orange and purple at the distributor.

You then need to set the timing manually and set the carb mix up manually. The carb does have mix screws hidden down front that might need a drill or saw to get at. When setting up the mix, I believe the stepper motor's pins should be in the middle of their travel where they work stock to get the proper high speed running.

The computer bypass is called the 'Nutter' after the gent that posted it. He set his carb pins full rich. This give lousy gas mileage and top end performance. You can try both. I can adjust my carb pins from up top with needle nose pliers or a mini screwdriver.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >

Thanks Mike & RoyJ....

RoyJ if you could email some good diagrams to snipped-for-privacy@bresnan.net I would greatly appreciate it. If you have a similar jeep and could take a photo or two of your engine showing the lines in place and where they go that would be a great help to go with them. I have some diagrams but being more of a visual person the actual thing would help put the diagrams to better use as well.

THanks all for the information and if others have more to add great.

Dave

If the computer has been disabled, you can save about 5 miles of vacuum lines and just hook up the 'needed' items for good running.... PCV, charcoal canister (gas tank and carb vent), EGR, distributor advance and air filter flaps for the heat pipe for good winter running.

You can tell by looking at the plugs on the ignition module 'waaaayyyy' down under the washer bottle on the fender. Look at the 4 wire connector and see if the purple wire has been hooked up. If it has, then the computer has been put to sleep, if the purple wire just terminates at the plug, then the computer is still in there and it needs a ton of vacuum switches to work right.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail >

Thanks again to Mike & Roy....

So a question I have then. If i don't hook up the stock vacuum 4wd what would be a good option that doesn't cost a lot of money to set 4wd back up on my Jeep. I've heard that the stock 4wd had some issues when getting wet or cold with the snow but not sure how common those issues are. Knowing my luck recently I'd encounter them though. I've also read where some guy rigged a chain with a lever to engage the 4wd but I don't want to do something like that because it seems a little worse off than the vacuum idea.

I thought I had read for $200 - $300 I could get a 4wd conversion for that jeep or something that would work out quite nicely and be better than what it came with and very reliable. Am I correct or just hearing/reading crap out there? I don't mind spending to much to get some good reliable 4wd because I do want to do some trail rides in the mountains of Montana here. Other things that I know I need to get done are the sway bar and bushings but not sure what else to look for underneath. The sway bar bushings (if i'm saying that right look horrible), and I've noticed the steering wheel kind of jerk or jiggle when driving at times, not to much give in the wheel while turning which is nice but more jerking type stuff when going over the tiny lines made in the road. If that makes sense. I've been putting a good shopping list together and hoping to order some things next week to get moving. I appreciate any and all suggestions but don't have unlimited funs for the "toy" either. I do have a hard top so one of the items will have to be a bestop bikini or something though when I take the doors and hardtop off in the spring/summer for crusing around.

Thanks again all. Dave

Most of the front axle discconect issues tend to be in the vac lines, the plugs, and the vac switch on the transfer case. The vac motor on the axle does go bad but not very often. The fast and dirty way to get the front axle into locked mode is to run a vac line from most any vac port on the engine to the center port on the axle vac motor. This will permanently lock the axle in 4wd mode. More wear and tear but this is the same mode as all the TJ's ('97 and up) use. Or you can spend the $$ and get the cable disconnect kit.

The steer> Thanks again to Mike & Roy....

I've read up on the 4x4 Posi-Lok and to me it sounds like a better and easier install option than fabricating with a bike chain or break cable as talked about in the other messages. Yes $190 compared to $20 but I would think that the Posi-Lok system might work a bit better. If I'm incorrect could someone let me know?

Also if I do the Posi-Lok which bypasses the vacuum actuator system for the 4wd could I then do the ignition mod (The Nutter Mod/Bypass) and then yank out all the extra crap underneath the hood as Mike states? The main quesiton I would have with that is does it affect any of my RPM, Fuel, Temp or other gauges by doing this?

One other thing I noticed is that the person that had it the last couple of years put a 2" lift on the body and has larger tires on the Jeep. So obviously the speedometer is incorrect when driving down the road and I found out the fun way. Going 60 MPH is what the gauge read but the officer told me I was doing 65 (since it was a 55 he thought he would let me know). Is there a quick fix since I'm using larger tires with the lift and everything and what would I need to know to buy the correct device to get my speedometer back in tune. Yes I know simple things but I'm learning.

Thanks again for any help.

Dave