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We checked many things on a dead 90 Mazda 323 HatchBack 1.6 L SOHC
fuel-injected with no success and NEED MORE IDEAS from someone:

The car was driven home from work normally and seemed  OK.

The next morning, cranked over normally, but would not fire at all.

Removed two plugs and grounded them and observed their respective
sparks which verified that the distributor rotor was rotating (i.e the
timing belt was not broken).

Removed center wire from distributor and noted that it arced 1/4 to
3.8" to ground, so spark seemed Hot enough.

We listened for the fuel pump to run in the tank and could hear nothing.
Removed the plug at the tank (under the back seat) and measured for
voltage but found none (voltage for the fuel gage sender was present
and fuel gage registered normally).

Noted that the Injection Relay (near the battery) was functioning (removed
cover and noted that it closed, and the +12 was indeed coming thru its contact
when the ignition key was ON). Here we were puzzled bcause although we did
not have a suitable wiring diagram, most similar diagrams seemed to show that
the injecter relay contact should send +12 volts directly to the fuel pump motor.
(some diagrams indicated an "inertia switch" between the negative side of the  
motor and ground, for collision protection, but our negative was grounded OK,
so that only +12 was required.

So we assumed that the wire from the relay to the motor might be intermittent
and we "hot-wired" the + side of the motor directly to the car battery by
forcing a common pin (or safety pin) thru the plastic wire to the + side of the  
motor, and connected the plug normally. The fuel injector motor runs whenever
+12 is touched to the pin.  We have removed the plugs and cleaned them, altho
they did not appear to be wet, or fouled with gasoline.

Our hopes were dashed when we still got the same results....turns over but no
firing.  It doesn't seem logical that more than one problem would occur overnite
but we proceeded to prove that we had pressurized fuel available in the
manifold for the four fuel injectors, so we temporarilly disconnected the
return line to the gas tank and substituted a pressure gauge. With the pressure-
regulator valve now blocked at the return side, we jogged the fuel pump with
the hot wire and found that the pressure could easily go past 70 psi, so we left    
it at 60 lbs.  When we cranked the engine, we watched to see that the original  
motor wiring didn't kick in and a try to increase the pressure (with no regulator    
functioning to limit it). Unfortunately, still the same result...cranks over
but refuses to fire.

So again, it doesn't seem logical that injector motor problems and ingnition-
timing problems could both occur overnite, but we now proceeded to check whether
timing was changed by the belt slipping.  Again, we are puzzled why we can't
find a reference mark on the crank-pulley that correlates with top-dead center
on cylinder #1 (passenger-side toward crank-pulley).  At any rate, we add our
dot of white paint opposite the reference group of lines on the block, and use
a timing light on cylinder #1 to verify that it fires at our white dot.

So it appears that only fuel is left. We earlier had cranked over with all the
plugs out and caught a modest fuel amount on wax paper, and later when we held the
manifold pressure at 60 lbs, we removed a previously cleaned plug and found it
saturated with fuel.

So what speculation is left: after all our several attempts, the engine
never fired  when cranking!  Is it possible that the computer is completely
out of synch and opens the injectors at the wrong time? It wouldn't be an injector
problem, because they wouldn't all go bad at once...it could fire on 3 cylinders.

It's a backup car and isn't worth much, but if we've tweaked your curiosity,
we would welcome any comments