High Altitude Compensation system (1 Viewer)

[Helipilot]

Need advice on installing the High Altitude Compensation system and is it a huge job? And does anyone know if this system is available. Cold weather has stopped my painting efforts for awhile so looking at fine tuning the chassis and engine stuff.

Thanks in advance for your comments.

 

[wscbill]

For 1977, High Altitude spec was an option like California spec. It included several different components from Federal or California spec. For some reason, my new FJ40, purchased at Skokie, IL in 1977 (now long gone) had the High Altitude spec option. If your 40 wasn't High Altitude spec to begin with, finding these parts may be difficult.

Carburetor - 21100-61090
Distributor - 19100-61110
EGR Valve - 25620-61050
VSV - 17650-61050
High Altitude Compensator (HAC) Valve - 25709-61010
There is also additional vacuum hose, a check valve (90917-10038) and a clamp (90461-10178) to hold the HAC

High Altitude spec vehicles had a special vacuum hose routing decal on the air cleaner intake.

High Altitude spec vehicles also had a special Emissions Data decal under the hood. Looks similar to the Federal version (black letters on white background), but with different tuneup specifications, and the last paragraph (This vehicle conforms...) reads "...at altitudes above 4000 feet".

 

[1911]

There is detailed info on the HAC in the 2F Emission Control Repair Manual, which can be downloaded from somewhere here on Mud for free. If you can't find it, PM me and I will email you a copy of my PDF.

My (11/79 build) 1980 came with it, and it was well worth retaining when I de-smogged it. It doesn't work any miracle, but it does help in the mountains by giving you quite a bit more ignition advance and thinning the fuel mixture a bit.

People that have de-smogged and kept the parts might be a source for you.

 

[GA Architect]

My '77 was one of the High Altitude vehicles sold in Colorado Springs. After I desmogged it, I sent all my HAC stuff to Georg. However, I did keep the carb and just plug the high altitude port. Do you have the high altitude carburetor?

 

[Helipilot]

Thanks wscbill for the detailed information and thanks 1911 and GA Architect for the additional info. As far as I can tell I have the standard factory carb. This truck was originally sold in California and five years later moved to Arizona where it spent the next 36 years. No rust and I have had it in my shop since I bought it with a lot of aircraft stuff in process. My business has kept me tied down and I have been working on it a little at a time.

 

[MoCoNative]

If you don't have the high altitude carb then you don't need the system. High alt carb will look similar to the carbs on the 80 and up FJ60's if you have access to one of those. I've been told they have some unique atrributes compared to the regular 77 carb, but nothing special. I'm currently running an FJ60 carb. I've tried hooking the HAC up in different ways, and really the only thing it helps right now is idle stabilization.

My house is at 6800 feet though and all my driving is around that too, in Arkansas you would not need it. The factory system only kicks in above 4000 ft. As I mentioned above it comes down more to tuning than anything. My FJ60 is all stock and runs great, with the stock HAC system. But when I hooked it all up on my 40 I get a lean surge issue during highway cruise. Why the 60 runs great with the airbleeds adding air and the 40 won't I don't know. All the HAC does is bleed extra air into the idle, primary and secondary curcuits when active, and advance the timing. It does this through the valve via a tiny filter. I'm just bleeding air to the idle circuit of my 40 with a hose, small nipple and fitting with similar filter material stuffed in it. I would have to cap it if I ever go too low, didn't have any issues in Moab, lowest place the 40 has ever been.

 

[GA Architect]

Here is what the '77 high altitude carb looks like. (looks like I took these photos with my old flip phone....)

 

[Spike Strip]

FWIW, the stock HAC valve is long NLA, but the HAC valve for a mid 80s 4runner/truck is identical to the above one, EXCEPT for the nipple on the bottom- it's just open to atmosphere without the nipple. However, the stock bottom cover (with nipple) fits on the 4runner one if you have a non-functional stock HAC valve.

I can find the part # if anyone is interested.

 

[cruiserboy14]

I am interested. I'm trying to reconstruct my HAC system..

 

[Helipilot]

Thanks for all that excellent information. I think I will start my search for an high altitude carb or an extra carb and have it tuned for high altitude to switch out when I go west. That would be, in my humble thought process, quicker than trying to re-jet out there and has been suggested by another forum member as the way to go on the high altitude thing.

 

[DSRTRDR]

how high do you need to go ?

I was easily able to do Eisenhower pass in CO with low altitude jetting

 

[1911]

FWIW, you can get 90% of the usefulness of the HAC system without having it by simply un-clamping your distributor when you get to the mountains, and manually turning it to get about 6 degrees more advance on your base timing. That's what the HAC system does automatically, though it also adds more air to the carb mixture. If you don't have a dial-back timing light handy, just advance it to where it runs best without knocking/pinging under load. It's a lot easier than swapping carbs, and can be undone in a minute when you're ready to go back home (if you remember to mark your original timing with a Sharpie line across the base of the distributor and the block, before you advance it).

how high do you need to go ?

I was easily able to do Eisenhower pass in CO with low altitude jetting

Not to be pedantic Claudia, but you probably mean Eisenhower Tunnel. Loveland Pass is the pass, that the tunnel goes under. Still, you did well - the highest elevation in the tunnel is 11,158'.

My experience (growing up in Colorado) is, if you have good compression, good vacuum, and a good valve adjustment to start with before you drive it to high altitude, you will do fine - but you'll have noticeably more power if you advance the ignition timing, either manually or by the HAC system.

 

[cruiserboy14]

I'm not doing this out of necessity. I'm simply trying to restore my vehicle to its original functioning spec. I have brought it a long way by working out kinks, sorting out problems and replacing or rebolting on original parts. I will eventually do a frame off restoration, but for now I want to get it back to how Mr. Toyota left it. I've been banging along quite well but have found this system to be almost an enigma on the forum, by that I mean everyone knows how it works but that's it. there's no searchable info unless you have a manual (which I'm hunting down as we speak). where can one find replacement parts? can you take similar parts of newer vehicles? what is the different configurations threw the years? I'm trying to make a searchable hub for newbs like me as I go.

 

[74fj40]

My experience (growing up in Colorado) is, if you have good compression, good vacuum, and a good valve adjustment to start with before you drive it to high altitude, you will do fine - but you'll have noticeably more power if you advance the ignition timing, either manually or by the HAC system.

Interesting... my experience growing up in Colorado and taking my 72 fj40 up i70, is if you stay in the far right lane, put your hazards on, and leave it in 2nd gear, you’ll do just fine.

 

[Helipilot]

All good information folks, thanks so much for educating me on this.