From: Wally Plumley [wplumley@bellsouth.net]
Sent: Monday, January 21, 2002 8:37 PM
To: gmnac@xtra.co.nz
Cc: john.pirtle@rennlist.com
Subject: 928 Problems

Brian wrote:
hello my name is brian cook i own a 83 928s auto and i am just
completing a cambelt change along with a removal of the cylinder head
to repair a snapped exhaust stud and i seem to have disturbed
something in the injection system my guess is a trigger pickup for
the injection system somewhere near the front crank pulley am i correct
in assumeing there is one in this vacinity as i appear to have fuel
pressure and no fuel being delivered along the fuel rail/pipes to the
injectors unless the flap imediatly below the air filter body is
depressed also what is that flap a sort of variable plenum chamber
device or a accelerator pump in injection ( i dont think so but just
guessing)your help would be much appreciated thank you

Your car has what is called Bosch AFC (Air Flow Controlled) Jetronic fuel 
injection.

The injectors are controlled by an ECU (Engine Control Unit), and the 
trigger signal comes from the electronic ignition box to the ECU (green 
wire from terminal 16 on the ignition box to terminal O7 on the bottom of 
the central power panel). There is no crank trigger.

The flap under the air filter box is the air flow sensor - It tells the ECU 
how much air is flowing, so the ECU can tell the injectors how much fuel to 
inject. (There are other signals to the ECU that also control the amount of 
fuel, such as temp sensors, WOT switches, idle switches, etc.)

If the injectors are not firing (you should be able to hear them clicking 
as the engine turns over with a tube in your ear or a stethoscope), one 
possible problem is relay XVI, the AFC Relay. There should be 12 vdc on 
terminals W2 (red/black), W3 (red/green), W4 (red/blue) and W5 (red) on the 
bottom of the central power panel with the ignition on. (The plugs on the 
bottom are lettered A-X, W is the next to last plug on the right.) This 12 
vdc comes from terminal 87 in relay XVI.

Wally Plumley
928 Specialists