1H-FT iNJECTOR PUMP MISTERY DIAPHRAM (1 Viewer)

[NZBJ71]

Hi All,

I recently upgraded from a 1991 HDJ81 to a 1996 HDJ81 with the 1HD-FT engine.

The 1HD-FT is a bit sluggish off the line and I'm going to tweek the fuel pin to see if I can improve it a bit.

There is a vacuum diaphram mounted above the injector pump and I can't figure out what its for. I hate no knowing what components on my vehicle do, so just to satisfy my own curioustity can somebody please advise what the component circled in the attached picture does?


Thanks

 

[CycloSteve]

My 1HD-FT had that, and no longer does. Not sure of its function, but no adverse issues with deleting. Others may chime in with the actual function and need.

 

[Rock40]

Hmmm, my FT had all the European emissions nonsense on it but it didn't have that bugger. Like Steve said, I'd just delete it. The only vacuum lines I'm running are for the boost sensors and the main vacuum lines which goes into the IP itself. I deleted a TON of other nonsense and it runs great. Nearly 15,000 miles and counting since the swap.....

 

[troopie]

It's a non egr thing, that's for sure.
I've wondered what it is myself, hopefully someone who knows will chime in cause i'm curious too

 

[roscoFJ73]

What do the hoses run to? I would guess and say it has to do with emissions. Is this a NZ/Aust spec landcruiser?

 

[gifu]

Does that run to the lower port of the fuel aneroid? And to the vacuum pump?

It might be the altitude compensator. At low altitude, vacuum is allowed through and helps pull down the fuel aneroid compensator pin (which is "normally" only pushed down by boost).
At high altitude, the vacuum is no longer allowed to pull the fuel aneroid down, thus de-fueling the IP and reducing smoke.

 

[Jan-78FJ40]

Does that run to the lower port of the fuel aneroid? And to the vacuum pump?

It might be the altitude compensator. At low altitude, vacuum is allowed through and helps pull down the fuel aneroid compensator pin (which is "normally" only pushed down by boost).
At high altitude, the vacuum is no longer allowed to pull the fuel aneroid down, thus de-fueling the IP and reducing smoke.

That is usually only needed on non-turbo engines, as the others have the boost compensation system for that.

 

[NZBJ71]

The vacuum line run from the vacuum pump and to the pump below the diaphram. So i think it must be the High Altitude Compensator.

Not sute how it knows its at altitude as it only has a vacuum line in and out?

 

[gifu]

the device has a disk/diaphragm in it that measures atmospheric pressure. If under (I think... 4000') it gives no vacuum to lower port on IP. If over 4000', it allows vacuum.
The spring pressure under the boost compensator diaphragm is set a bit higher than a pump without it... so that under normal operation (ie: under 4000'), it "needs" vacuum to get "enough" fuel.
If you decide to delete it... you should:
1) adjust the spring tension under the boost diaphragm (you should do this anyway, it's way too stiff from factory. see the thread in this forum about IP adjustment for 1HDT/FT) to compensate
2) ...and make sure you don't just "cap" the lower port... you want it to breathe a little so the fuel comp diaphragm can easily be "pushed" by boost
3) ...or connect a VSV to that port and vacuum, and put a manual switch on your dash (or hidden) so if/when other people drive it (or when you visit high altitude places) , you can switch off the "extra" fueling. I think they used to call this Valet Mode on the Corvettes.

I personally need to do #3. When I'm at high altitude (currently visiting Flagstaff AZ... 7000') my truck is quite smokey (I have my fuel turned up quite a bit).

 

[CycloSteve]

After driving my rig for the first time at altitude post-diesel conversion, I will be adding the manual BACS diaphragm back. The truck ran fine, but definitely had quite a bit more soot/overfueling. Startups were quick enough, but not what I would call environmentally sound.

I was at 7,300' and the temps were under 20 degrees F. Manually glowing the screen for 10 seconds prior to cranking over. Needed to idle for about a minute to allow the motor to smooth out. I will be back up there in under a month, and will see what a difference the manual BACS system makes.

Here is the thread where I have been posting my progress with the BACS system re-installation and testing.

1HD-FT /1HD-T pump