I have read and posted on many threads where people run into issues with fuel injected 5 litres.
This is a basic guide on problem solving. It doesn't have all the answers, but it should stimulate a few brain cells
and help you work it out for yourself.
There are a few things I would recommend to anyone who has one or will be fitting one in the future.
1) A basic 12 volt test lamp - A cheap way is to use an LED and 560 ohm resistor in series.
2) A reasonable digital multimeter that has voltage, resistance and continuity functions.
3) A Gregories manual. - #258 for 1989-1991 V8 commodore actually has a reasonable wiring diagram.
4) The GMH VP and VQ service manual No.4 (AKA the must have blue book)
5) Beer and patience ! - Use a step by step approach of fault finding.
Most issues of non starting 5 Litre's fall into 3 categories.
1) It wont turn over at all.
Check the battery is charged (multimeter on volts)
Check you have +12 volts at the starter motor solenoid. (multimeter on volts)
Check the earth connections are tight (multimeter on continuity - one lead on -ve batt terminal and other lead can probe earth points)
Check there is +12 volts at the violet wire to the starter solenoid when key turned to start (multimeter on volts)
No voltage at violet wire ? Check starter relay.
Is the car auto ?, check park/neutral start safety switch
2) There's no fuel
Follow the path of the fuel from tank to engine
Check you have enough fuel in the tank (at least half a tank)
Check fuel pump wires are connected (don't laugh, ive seen this done twice !)
With the key turned to IGN, the fuel pump should run for a few seconds and then stop (this is normal)
Check fuel pump relay (page 98 of the Gregories shows you how)
Is there enough fuel pressure ? (280 - 320 kpa, follow safety instructions in Gregories to test this)
Are the injector wires connected ?
3) There's no spark
Verify +12 volt at ECU with IGN on
Check earth leads
Check coil and its connections (check coil body for cracks, is common when their stuffed)
I have seen numerous examples of ignition failure that all involve coil + ignition module + halls effect trigger in distributor.
If an ignition module fails, there is a high chance that the halls effect trigger will fail and/or the coil as well.
If the ignition module is found to be at fault, change the halls effect trigger too.
You can buy the halls effect trigger on its own and install it easily in the distributor yourself (Gregories page 97)
Schultz auto electrics in Perth is where I source mine from.
Make sure you have fitted the engine check light.
This is an invaluable tool for fault finding using the GMH VP and VQ service manual No.4 (AKA the must have blue book) mentioned above.
It looks like this
And has diagnostic flow charts and information set out like this