85 fj60 help!! Stall/hesitation when only 2k high elevation (1 Viewer)

[Cruiserompin]

Hello all!
About a month ago i drove my truck a wee but ways into the mountains which sits at about 7200ft elevation, and i live at 5200ft.
We drove about 1.5 hours to get there without a single problem, cruising on the highway at about 60mph. The first stop light i came to after getting off the highway my truck idled fine but the minute i went to get going, anything about 1k rpm my truck would hesitate and stall if i didnt push the clutch back in and let off the gas. Ive read about the HAC valve but i dont think that is the problem since i live at 5200ft. My truck no matter what i did would not allow me to get going. I pulled into a parking lot and got a tow home. When i got home i started my truck and went for a 20 minute drive with no problems. Its been being daily driven every day since. I dont know where to begin when it comes to tackling this issue.
My motor is all stock and has 170k miles. Only recent maintenance ive done is a new gasket between the j-pipe and egr cooler.
Any help would be much appreciated!

 

[OSS]

Hmmm-
Basically two things happen when the HAC system activates at about 4000 ft, extra air is allowed to flow into the carb and the timing is advanced.
But you're already at 5200 ft, so your HAC system SHOULD be in the high altitude mode already.

Check it.
There's troubleshooting procedures in the emissions FSM. Maybe yours isn't functioning correctly or hooked up correctly?

 

[Cruiserompin]

Hmmm-
Basically two things happen when the HAC system activates at about 4000 ft, extra air is allowed to flow into the carb and the timing is advanced.
But you're already at 5200 ft, so your HAC system SHOULD be in the high altitude mode already.

Check it.
There's troubleshooting procedures in the emissions FSM. Maybe yours isn't functioning correctly or hooked up correctly?

Yea ill check it, the truck is originally from about 8800 came down here to 5200 and hasnt much changed. Drove up to 11000 not to long ago with out any issues. Ill check it. Thank you.

 

[FJACS]

Test the HAC, and verify the timing is set up correctly. If the HAC fails the test and you’re always above 4000ft, you could disable the HAC system and run the advancer port on the carb to the outer vacuum pot on the distributor.

 

[OSS]

That'll only advance the timing 6° when the gas is on the pedal. The HAC system pulls in the outer vacuum diaphragm at altitude whenever the engine is running, even at idle. So a workaround (if it fails) would be to connect a vacuum hose from manifold vacuum straight to the distributor outer vacuum actuator.