On top of the diaphragm housing is what looks like a core plug, beneath this is the
low manifold pressure delivery rate adjustment. If the cap is carefully prised out
using two small screwdrivers, it can be replaced after adjustment with a couple of
drops of threadlock.
The adjuster is a torx headed screw with a 13mm hex locknut. Turning this screw
clockwise increases the off boost fuel delivery, increasing low down power. 2 turns
clockwise will give a noticeable improvement in low down power, further adjustment
will give more power but also more smoke. If too much smoke is produced, back off
2) Part boost fuel delivery adjustment (automatic fuel control, AFC).
This is effected by removing the four screws retaining the top of the diaphraghm
housing. Carefully remove the cover, beneath which you will see the diaphragm. Attached
to the underside of this is an eccentric cone which controls the fuel delivery pin,
The further out this pin can travel, the more fuel is delivered. As more boost is
applied by the turbo, the diaphragm is forced downward, causing more fuel to be delivered.
This adjustment will give more mid-range power (3rd / 4th gear acceleration)
There is a punch mark on the disc atop the diaphragm, mark this relavent to the housing
before beginning. Maximum fuel delivery is at approx 120° clockwise from stock,
90° is a good starting point. After this adjustment, it may be nessacery to re-adjust
the off boost screw to reduce smoke.
Remember that the further the diaphragm is turned, more fuel will be delivered, more
smoke produced, and the EGT will rise faster and higher.
3) Maximum boost fuel delivery adjustment (automatic fuel control, AFC).
Beneath the diaphragm, at the base of the spring is a large serrated ring. This
ring applies pre-load to the spring, therefore setting the boost required to achieve
maximum fuel delivery. It can be turned with the aid of a small screwdriver, there
is a pawl that prevents it from turning in use, but will not prevent it from being
turned manually, it will just 'click' round (like a ratchet).
Turning it clockwise (down) will allow maximum fuel sooner (lower boost), anti-clockwise
will mean more boost is needed for maximum fuel. Again make the adjustments in ¼
turn increments and check for smoke!
You can judge how much adjusment is needed by looking at the wear mark left on the
taper left by the fuel delivery pin. If you have, or intend to increase the boost
pressure, this is unlikely to need adjustment as the increased boost will push the
diaphragm further down anyway. It may in fact need turning anti-clockwise to counter
the boost and reduce full throttle, low boost smoke.
4) Maximum Power adjustment.
On the rear of the pump, in amongst the fuel lines is another adjustment. It has
either a plastc cap, lead seal & wire or welded collar. This is the maximum power
After removing the seal, and loosening the locknut, turning the screw clockwise upto
2 turns will increase the maximum power. After this adjustment it may be nessacery
to re-adjust the low boost/smoke adjustment screw and the idle speed/throttle linkage.
BEWARE, this adjustment allows the engine to give more top power, increased RPM,
heat & very high EGT at full throttle.
5) Adjusting the smoke!
Assuming injectors, pump etc. Are all in good order, if not rectify first.
If you have smoke at:
Full throttle under load, back off the full power adjustment
Low revs under load, back off the low boost adjustment*
At start up / idle, fine adjust the low boost adjustment
*if you have over adjusted the AFC serrated ring, you will be acheiving full fuel
delivery too soon. You will need to back off the adjustment.