High altitude compensator 1HZ retrofit? (1 Viewer)

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Old Dirty Beard said:
Any life left in this HAC testing thread? Wondering if it is worth the energy.
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That's a good question. I've changed so many variables since I did the HAC that I might not be able to speak to changes in it. I had my pump rebuilt (with the HAC already retrofitted on top) and was also tracking down some air in the system that came from the pickup tube in the fuel tank. Replaced all the fuel lines.

I'm now at what I hope is the last stage of tuning, post injection pump rebuild.

I do think it's worth the effort if you live or spend any time at altitude. But this is more of an opinion based on subjective factors at this point than any real scientific trials. Ultimately I see less smoke at altitude for a given fuel trim than I did previously.
 
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If anyone is looking for a HAC I just received a few take offs from 2023 HZJ78’s that I will be listing for sale soon.
B8C5F4F0-1E58-45C9-8661-720C93D88265.jpeg
9B5CF045-6C66-409E-BE6B-CB9DB71757EA.jpeg
 
JDM Journeys said:
Thanks to all who have contributed here. The last of my parts came on Friday, so yesterday it was time to dive in. I had a complete seal kit (for bosch ve pumps), a new fuel pipe assy, and of course the compensator itself.

View attachment 3148195

I should preface by saying I did this all in situ. Its doable, but awkward at times.

First things first. Remove the old cap. The FSM shows so-so detail, but in essence, you need to remove the four perimeter bolts (5mm allen key I think), and also the a/c vacuum idle up thingy on the side (three more bolts). Pulling the forward battery and the throttle linkage is also a good idea for access. And of course the two fuel hoses have to be detached.
View attachment 3148203At this point you can lift the cover partway off, but don't get carried away. Once you've lifted one edge, detach the spring from under the cover. The details of this spring are in the service manual, but the other end has another spring and a pin, so be careful. Lots of small parts to go flying.

Okay, the cover can come off now, and you can dive into the bag of washers, orings and seals.
I replaced the main cover seal, as well as the oring on the throttle control shaft once I removed it from the old cover (required light tapping to get it out, with soft hammer). Also fitted new copper washers either side of the fuel pipe, and a new washer behind the fuel screw. I counted the turns on the fuel screw as I removed it, so I could get it back in approximately the same spot.
View attachment 3148216

I mistakenly thought that the idle and max speed limit screws would go back in the same place but as the pic above shows (where I have them in wrong) the covers differ in their castings in that area, so I had to reinstall both screws after the fact. I was worried about the hoses not being the right length so I clocked the new fuel pipe until it seemed to work with both, although the smaller diameter hose up top was a trifle long (that's a good problem). Here's the orientation that seemed to work:
View attachment 3148222

I did notice a little dirt in the banjo bolt so I picked and sprayed it out thoroughly before reinstall.
Then it was time for reinstall. I had removed the throttle control plate before removing the cover, but this would have been better done on the bench for both removal and reinstall, methinks?

View attachment 3148227
At this point, you have to somehow get the spring reattached to the linkage, clear the intake with your new taller stack, and get the bolts back in, while overcoming the resistance of the springy linkage pushing up on the underside. Not easy.
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Do you happen to have a part number for that bag of o-rings and gaskets?
 
joekatana said:
If anyone is looking for a HAC I just received a few take offs from 2023 HZJ78’s that I will be listing for sale soon.
Click to expand...

I may snag one of those from you, so please keep me in mind. Anytime I'm on a hill above 2,200' or so, I'm seeing decreased performance; I don't even like thinking about having taken my 73 up to 11,000' a few months ago. I'm pretty sure that run taxed it so hard that I need to get inside and clean things up.
 
Rigster said:
That is exactly what this is for. @JDM Journeys put this on his 1HZ naturally aspirated engine fuel pump. Read through the thread for further information. :cheers:
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Yep. Installing it on the pump in situ is not for the faint of heart but is doable if you're careful and skilled (or patiently stubborn like me, who's definitely not skilled).

Seems like on later models it was a lot more common than earlier ones.

The only caution I would issue beyond the actual install is this... If you are planning to turbo down the line then don't do an HAC. Just skip to a boost compensator. I think it will still help at altitude even turbocharged, better than an atmo pump, but not much. Compensator can be tuned, and you can debate with the cool kids about springs, aneroids etc. 🤣
 
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joekatana said:
If anyone is looking for a HAC I just received a few take offs from 2023 HZJ78’s that I will be listing for sale soon.View attachment 3356014View attachment 3356015
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I would like to buy one of those if they are still available. I got back from a trip to Colorado recently and I’d like to do everything I can short of a turbo. I’m in NC, let me know if one is still available. This is a super helpful thread, thanks to all!
 
So I stumbled across what seems to be HAC injectors. Any ideas about what Toyota thinks about this? They must be different at almost double the price. Different pop-pressures perhaps?
23600-19035
Holder & Nozzle Set, Nozzle
[08.2016 -] 1HZ..HZJ76,78,79..RHD SOUTH AFRICA&HIGH ALTITUDE COMPENSATOR-WITH
 
Have people added a reference pressure port to the top of the HAC to sense boost pressure? Can one just buy the top cap used on a boost compensator?
 
I found a new HAC that came off a 2019 HZJ79, seller states it will fit 1999 to current 1HZ.

I have a 1998 HZJ105, and wondering if it will work on the 1HZ???

Any help would be greatly appreciated.
 
Think I found my answer...

  • 1998 1HZ:
    This engine featured a mechanical injection pump and injectors, a design known for its simplicity and durability.

  • 1999 1HZ:
    The 1999 model year introduced an electronic fuel injection system, which improved fuel economy, emissions control, and overall refinement.

  • So maybe the HAC is different???
 
There's no EFI on a 1HZ...
Also you should page @JDM Journeys - he did a HAC swap but ultimately turbo'ed his engine in any case... That's probably the "high altitude" compensation you need if you're looking for more power, etc.
 
janyyc said:
There's no EFI on a 1HZ...
Also you should page @JDM Journeys - he did a HAC swap but ultimately turbo'ed his engine in any case... That's probably the "high altitude" compensation you need if you're looking for more power, etc.
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I'm at 8700-feet eleven. Even though I have plenty of power and torque off-road, I would like to have just a little more power on the long uphill pavement runs where I'm rolling-coal because I have my foot into it.
 
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