robfg67 Posted September 7 Share Posted September 7 I have a '90 with the 4.0L and 4WD. Recently, the Part Time 4WD light has not been coming on while in 4WD. Yes, the 4WD engages and disengages as it should and the CAD is factory untouched. Where should I start my troubleshooting? Link to comment Share on other sites More sharing options...
llhat Posted September 7 Share Posted September 7 logic would be to 1. test the bulb 2. test the power to the bulb with 4wd engaged wiring indicates a vacuum operated switch sends the signal... possibly on the transfer case, though I cannot determine its location makes a difference in connector number ... automatic versus manual transmission. Link to comment Share on other sites More sharing options...
Gojira94 Posted September 7 Share Posted September 7 Might be helpful, this guy @WAEMID IVis a Club member. One of the best dissertations on CAD, its vacuum, and indicator light I've ever seen: 4x4 dashboard light Link to comment Share on other sites More sharing options...
robfg67 Posted September 7 Author Share Posted September 7 (edited) 5 hours ago, Gojira94 said: Might be helpful, this guy @WAEMID IVis a Cub member. One of the best dissertations on CAD, its vacuum, and indicator light I've ever seen: 4x4 dashboard light Thanks for posting the video. The white line is what attaches to the vacuum switch mounted near the firewall by the passenger side and it appears as if I don't have any vacuum on the white line. I pulled the hose off that switch and ran a new hose from the switch to my vacuum pump and with the 4WD engaged and engine running, the PART TIME light came on. From that video, the blue line hanging empty in the picture is normal because that is how the system releases vacuum. However, there is an open female port under the truck near the CAD and in the same passenger area near the blower motor. Can anyone confirm if these two ports should be open? Edited September 7 by robfg67 forgot a picture Link to comment Share on other sites More sharing options...
robfg67 Posted September 8 Author Share Posted September 8 STATUS UPDATE: I ran a new 1/4" line from the vacuum switch under the coolant bottle to the white male port coming off the shift motor at the axle and the PART TIME light did not come on with engine running and in engaged in 4WD. I tested the hose at the vacuum switch with engine running and 4WD engaged with a digital manometer and it is pulling vacuum, but not much. It was about .024" of water column. Again, when I tested the vacuum switch with a vacuum pump a couple days ago (which pulls a lot deeper) it turned on the PART TIME light. I also removed the transfer case vacuum plug and the pintle seemed to move freely to me. Lastly, although this Jeep is 35 years old, it only has 40k original miles and is in MINT condition. Any thoughts? Link to comment Share on other sites More sharing options...
89 MJ Posted September 8 Share Posted September 8 What is the vacuum at the port that it uses on the engine? Link to comment Share on other sites More sharing options...
robfg67 Posted September 9 Author Share Posted September 9 10 hours ago, 89 MJ said: What is the vacuum at the port that it uses on the engine? Is that port on the shift motor? If so, would that be the front port? Link to comment Share on other sites More sharing options...
llhat Posted September 9 Share Posted September 9 looks like some troubleshooting procedures in that scan above... but seem to be cut off......... can the full pages be scanned? Link to comment Share on other sites More sharing options...
89 MJ Posted September 9 Share Posted September 9 2 hours ago, robfg67 said: Is that port on the shift motor? If so, would that be the front port? No, the vacuum should be coming from a port on the engine, then likely going to a vacuum canister, and then to the transfer case. I would check it at all of those points. Link to comment Share on other sites More sharing options...
RG67MA Posted September 9 Share Posted September 9 Ilhat, yes there are troubleshooting instructions on those pages and no, I haven't followed them yet. I want to know if the system has enough vacuum first. 89MJ, not sure where to test for enough vacuum. I placed my digital manometer on the vacuum motor in front of the airbox and got 0.0. I know there is vacuum because I have no idle issues, the hvac works, and it shifts in and out of 4WD. The truck doesn't have cruise control. Link to comment Share on other sites More sharing options...
89 MJ Posted September 9 Share Posted September 9 16 minutes ago, RG67MA said: 89MJ, not sure where to test for enough vacuum. I placed my digital manometer on the vacuum motor in front of the airbox and got 0.0. I know there is vacuum because I have no idle issues, the hvac works, and it shifts in and out of 4WD. The truck doesn't have cruise control. There are vacuum ports on the intake. One of those should be for 4wd. I don’t know which one, you’ll have to trace your 4wd vacuum lines to a vacuum canister and then from the canister to the engine. Link to comment Share on other sites More sharing options...
RG67MA Posted September 9 Share Posted September 9 Ok, I will look for the correct vacuum port on the intake manifold next and report back. Thanks. Link to comment Share on other sites More sharing options...
llhat Posted September 9 Share Posted September 9 there is a vacuum line on the passenger fender, at one spot will have a 'tee' for cruise control.... and it supplies vacuum to the hvac box it follows the fender behind the battery down to the canister on the bumper. Question........ when you have your heat or even A/c operating, and you hit a hill or accelerate, does the air output 'switch' on its own to the defrost ducts on the windshield? If it does, that is a sign of weak vacuum/ cracked canister, or a hole in the hose... Otherwise I'd think you would have enough vacuum supply for the shift device and associated parts... On the intake manifold there's probably at least 3 sources of vacuum... as seen above.. supplying the fuel pressure regulator and in combination supplying the EGR supplying the rear CCV fitting on the valve cover that rearmost fitting is probably the source for the rest of the vacuum systems.... on the other schematic, there's the switch on transfer case... should be a vacuum supply to it, as that switch re-directs vacuum based on shift position.... Link to comment Share on other sites More sharing options...
robfg67 Posted September 9 Author Share Posted September 9 27 minutes ago, llhat said: there is a vacuum line on the passenger fender, at one spot will have a 'tee' for cruise control.... and it supplies vacuum to the hvac box it follows the fender behind the battery down to the canister on the bumper. Question........ when you have your heat or even A/c operating, and you hit a hill or accelerate, does the air output 'switch' on its own to the defrost ducts on the windshield? If it does, that is a sign of weak vacuum/ cracked canister, or a hole in the hose... Otherwise I'd think you would have enough vacuum supply for the shift device and associated parts... On the intake manifold there's probably at least 3 sources of vacuum... as seen above.. supplying the fuel pressure regulator and in combination supplying the EGR supplying the rear CCV fitting on the valve cover that rearmost fitting is probably the source for the rest of the vacuum systems.... on the other schematic, there's the switch on transfer case... should be a vacuum supply to it, as that switch re-directs vacuum based on shift position.... No, the hvac has never switched to defrost on its own. When I apply vacuum from my vacuum pump to the hose that attaches to the vacuum switch, the PART TIME light on the dash comes on. Link to comment Share on other sites More sharing options...
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