One for Toyota Turbo Gurus (gurii?)

Hi all,

I'm not right up my Toyota engines so, when I just looked at a 78 series Troopy with a N/A 4.2 diesel (1HZ), I was surprised to see a diaphragm chamber on the top of the VE-type injection pump. The chamber has no hose connection to the top of the diaphragm.

So, you Toyota technical gurus out there, do you know:

a ) Is it an unused manifold pressure compensator (and do Toyota therefore use the same pump on the 1HD-T and 1HD-FT factory turbo engines and simply fit a different diaphragm cover?

or b) Is it just an aneroid diaphragm for high altitude fuel correction?

If a) is true, do some/all aftermarket turbo kits provide a new diaphragm cover with a boost pressure connection?