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4wd light flashing on dash

  • project90
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03 Nov 2012 17:11 #52089 by project90
4wd light flashing on dash was created by project90
hi, the 4wd light on the dash is flashing on my wifes jimny so trying to sort it out with out taking it to a garage, i have done a bit or trawling on google and these forums about the problem and all say its the vacuum system failing.

so it was in getting the clutch replaced and i asked the mechanic to have a check while he was under, he cant see any visible leaks in the pipe work but said there wasnt even any suction out of the control box.

so is it worth checking any thing else before i start ordering parts? i know there was a detailed bit on this forums about the vacuum system and to check the little filter on the system if doing them doesnt fix it am guessing i will need spares.

I also got a garage to check the hubs and they weren't engaging either even when rigged up to a vacuum system so is it posible to just take them off and soak them in oil try free them up and put them back on or again is it better getting replacements, she wasn't intrested in the manual lock hubs so would need to be auto 1's again

sorry for babbling on but i dont really know alot about these jeeps and trying to get it sorted incase there is a bad winter this year and the wife wants the 4wd working as we moved out to the country last month. Aslo trying to keep it as cheap as possible so is ther any opinions on getting stuff from ebay? the shop was Cam Suzuki he had alot of stuff in and tihnk he offers a warranty on parts bought

cheers guys any input welcome and will try keep you posted if i get it fixed

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  • markyp2000
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03 Nov 2012 17:22 #52092 by markyp2000
Replied by markyp2000 on topic 4wd light flashing on dash
what year and engine do you have

if it a single cam engine like mine there is a vacuum pipe coming of the inlet manifold down by the fues box near the battery check that for splits then follow the pipe work down to the valves and have a look at them pipes

the hubs shouldnt be stuck its normaly the vacuum system that givs the problem

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  • project90
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03 Nov 2012 22:50 #52176 by project90
Replied by project90 on topic 4wd light flashing on dash
its the 1.3 petrol 03 plate. i shall check the hubs non the less its just 6 torx bolts i guess they just pop off after that

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03 Nov 2012 22:54 #52178 by markyp2000
Replied by markyp2000 on topic 4wd light flashing on dash
yes thats right
is say its more if an air leak/split pipe some where

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  • project90
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04 Nov 2012 10:04 - 04 Nov 2012 10:05 #52202 by project90
Replied by project90 on topic 4wd light flashing on dash
lets hope so :D

will the splits be seen quite easily? or can u rub like fairy liquid on them to finbd leaks easier?

also to find the leaks would i just turn engine on put in 4wd and might feel them?
Last edit: 04 Nov 2012 10:05 by project90.

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04 Nov 2012 10:46 #52205 by facade
Replied by facade on topic 4wd light flashing on dash

project90 wrote: will the splits be seen quite easily?


Yes in the rubber, especially if you flex it

project90 wrote: or can u rub like fairy liquid on them to find leaks easier?


No it is a vacuum system so no bubbles will blow + see below

project90 wrote: also to find the leaks would i just turn engine on put in 4wd and might feel them?


No, the system only applies vacuum for a few seconds not all the time.

Most likely place for total failure is the pipe from the manifold to the valves, as markyp2000 says.

You could disconnect the pipe at the manifold and plug the engine end, then remove and manually lock the hubs and replace them carefully and it will work, but this is really only a temporary measure.

Get something that will suck a vacuum about 50ml worth- I have a 100ml syringe.
Whip a wheel off and you will see 2 pipes to the hub, disconnect them and apply your vacuum to the spigots you should hear the hub click into place as you suck on each spigot in turn (it only works once in each direction, keep swapping over.)

If that works you can try the same procedure at the rubber pipes where they come out of the valve block.


Mine had a leaky "unlock"valve. This prevented any vacuum forming in the "lock" circuit.

If it suddenly breaks, go back to the last thing that you did before it broke and start looking there :)

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04 Nov 2012 17:17 #52241 by jonplace
Replied by jonplace on topic 4wd light flashing on dash
if you follow the air pipes up the radius arm they go to rubber pipes, you can carefully prize off the rubber pipe and suck on each pipe (one at a time) with your mouth, they should 'click'
you probs wont be able to blow down hard enough to reverse them, i found a foot pump with worked. when my vacuume system packed in i used this technique for a while. people would laugh as i used to get under the car at each offroading event and do the same before driving home at the end of the day to manualy blow / suck the hubs in and out !!

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04 Nov 2012 17:19 #52242 by jonplace
Replied by jonplace on topic 4wd light flashing on dash
just to add if the car hasnt been in 4wd for a long time they may just have seized and need a bit working to free them up

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  • markyp2000
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04 Nov 2012 17:21 #52243 by markyp2000
Replied by markyp2000 on topic 4wd light flashing on dash
how could you pump them on thay work on vacuum for a few seconds to go on and off

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04 Nov 2012 18:23 - 04 Nov 2012 18:28 #52248 by facade
Replied by facade on topic 4wd light flashing on dash
Blowing will make them work the opposite way round.

They are actually blown over by the pressure of the atmosphere acting on the side where there is no vacuum (the vacuum takes the pressure away from one side).

I would be careful about blowing them with a tyre pump or airline though, you may blow a seal out somewhere if you use more than a few psi.


How the system actually works (and what went wrong with mine)

There are 2 pipes to each hub. Each pipe goes to one side of the diaphragm inside the hub. One moves it out, the other moves it in. The hub has a bias, so once it has moved it clicks into place and stays in/out.

The two pipes run to 2 solenoid valves.
Each valve has 3 spigots.
1=atmosphere (has a little filter cap on it)
2=vacuum (both valves join together, and connect to the manifold tapping, as well as a small tank under the wing. There is a non return valve between the tank and the manifold too.)
3= the line to the hub (each valve controls one side, the "in" has a vacuum switch attached that works the 4wd light.)

When switched off, ports 1&3 join, and port 2 is sealed, so a vacuum builds up, and both sides of the hub are open to the air.

When you select 4wd

The lever moves the gears in the transfer case, and activates the 4wd switch. This signals the controller that 4wd has been selected.
The controller activates the "in" valve, joining ports 2&3, so vacuum reaches one side of the hub.
Atmospheric air goes through the other valve- ports 1&3 to push the hub over with a nice "click"
The vacuum built up in the line to the hub now switches the vacuum switch and the 4wd light comes on. (if no vacuum builds up within 5 seconds due to a leak, the light flashes, the hubs likely didn't move as there was no vacuum)
The "in" valve is released after a few seconds.

Select 2wd

The lever moves the gears in the transfer case, and the 4wd switch turns off.

The "out" valve is activated- ports 2&3 join, and vacuum is applied to the diaphragm, air enters through the "in" valve and pushes the hub over with a "clack"
The "out" valve is released after about 10 seconds. There is no monitoring switch for "out"


In my case, the "out" valve leaked all the time between ports 2&3 so there was never any vacuum built up in the tank and the hubs didn't pull in.

There is a lot to go wrong.

Blocked filters wont let air in to push the hubs over. Leaky pipes will not apply the vacuum.
Changing the kingpins usually blocks up the air passages inside the hub (remove black hub and blow through each spigot in turn to clear)
Leaky solenoid valves.
Wiring fault (unlikely)

Most people give up and fit manual activated hubs.

The flashing light does not affect the transfer box operation as this was a mechanical lever, if you can jam the hubs "in" the 4wd will work just fine.

If it suddenly breaks, go back to the last thing that you did before it broke and start looking there :)
Last edit: 04 Nov 2012 18:28 by facade.

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  • project90
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06 Nov 2012 14:36 #52463 by project90
Replied by project90 on topic 4wd light flashing on dash
ok, printed out the blog thing from this site about all the piping ect so going to give it a good looking over the next nice week end.

took hubs off, drivers side 1 was trashed, its like some 1 tried to fix a new set of rings to them and used a hammer so was all rusty in side.

going to get a new 1 and hopfully follow on from there

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08 Nov 2012 12:33 #52635 by project90
Replied by project90 on topic 4wd light flashing on dash
well replaced the drivers side hub with the 2nd hand 1 i got for £20 delivered was in much better conditions than old 1, had a good look today in the engine bay took battery out removed the fuse box bracket the lot.

firstly i was getting vacuum from the manifold, i take it thats constantly sucking, took the blue valve thing off again guessing its a 1 way valve. the tubes seem to take some pulling to get off that black plastic bit where all these rubber tubes are connected its there an easy way to do this or is it simply pull til they come off?

Any way when you follow them down there is like a big cross section or rubber tubes with 1 going in to some sort of grey valve that has a little filter on the side ( please can you let me know what this is and if this can be faulty/broken).

2 more pipes feed to 2 blue like relays which i couldnt seem to disconnect the wires from what are these and can u take them off if so how and what with. again if they do come off should they have any current through them when the 4wd system is engaged?

i have managed to find an ex suzuki mechanic to come give me some pointers on the system and what I'm looking at but guessing with out spending a few hours on it and really looking through the system he's not going to be able to see much more than i was.

Can some 1 also tell me what the solenoinds actually look like to get the multimeter on to again am looking at the diagrams from here www.bigjimny.com/images/documents/Check_the_vacuum_system.pdf
or any other pictures that people can link would be great

thanks guys, think my option might have to be to take it to the stealers and get them just to fix it. but still determined to crack it myself

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