Join Date: Jun 2005
Location: Port Ludlow, Wash.
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Re: 1986 F-250 6.9 L injectors
Injection quantity in a diesel is controlled by the IP, not the injector. This is in contrast to a gasser, which uses a fixed pressure and injector ON time + orifice diameter to control fuel quantity.
However, the different injectors used on our engines are rated for different fuel volume. This means that if you use a lower-volume injector at a high IP volume setting, the pressure on it will be proportionally higher -- or something will break. That's the nature of hydraulics.
The 'B' injectors are supposed to have longer spring travel, a larger orifice, and lower (1425 PSI) opening pressure. These were offered in conjunction with a higher compression ratio (pistons .003" higher, whoopee!; larger swirl cavity in the pistons' crowns; smaller precup chamber in the head -- making the heads non-interchangeable from '83 to later engines; smaller volume precups), and recalibrated fuel curve in the IP to work with lower opening pressure injectors.
I don't know the 6.9l very well, but based on this (published) information, I personally wouldn't mix 'A' model parts (IP, injectors, pistons, heads) with later lettered parts, with the possible exception of a later IP & injectors -- as a set.
Al S. firstname.lastname@example.org
1984 F-250 4x4 C6, BW1345, 3.54 D70, XLT extra cab, box-stock so far.