1984 XJS Injectors not firing

New coils x2 just put another new module in the amplifier just in case all contacts clean and working fine
All new plug leads (numbered) all new plugs with correct gap.
New base-plate in distributor and new pickup in distributor.
New rotor arm and distributor cap.
I will now go check timing 10 degrees BTDC
Thanks again for your trouble clive.

Work on this project suspended, will update you when checks completed in the meantime thanks once again your input is invaluable. clive

You can take it the problem is either power, or Gnd to the amplifier, the rotor to pickup distance is incorrect, the pickup isn’t producing an AC voltage, the new amplifier is dead, or there is a wiring fault between those devices, or the coil negative.

No point looking at anything else until you confirm those items are functioning and able to create the timed Gnd shunt the coil needs.

As and when you get back onto this try to remember the pickup and amplifier effectively replace the points of a conventional system, without the open/closed cycle the coil won’t fire.

First things first, my thanks for all the reply’s to my problem some of the diagnostic tests I would never dreamed of doing.
From the various tests that I have carried out, even checking items that I knew were OK and working fine, all have returned a positive result, except one… the continuity test from Lucas amplifier to ECU in the trunk.
I started from the beginning and covered all bases everything has been renewed or replaced that would be needed for the engine to run, which itr did for 30 minuets, but I now seem to have an electrical problem. This is not rely my scene so I am now asking for directions and what to do next. Thank you all once again for your help in diagnosing the fault,the next step is to correct it. … Clive

Two tests you need to do
First to see if it has a short to ground.
Second if it has continuity to the ECU plug, pin #18.
Both very easy with a multimeter.

We still don’t know what year and engine your car is.
Update your profile, it will help you a lot.

Year 1984 V12 HE 112 miles on the clock Lucas Ignition.

I do not understand how to access my profile. The tests you suggest what are they and how do I do them ? … clive

Click on your picture, top right, then the little person icon on the bottom, and go to preferences.

It’s just a continuity test with a multimeter.

Amp cable (disconnected) to Ground: No continuity (infinite Ohms)
Pin #18 at ECU plug (disconnected) to Ground: No continuity (infinite Ohms)

Amp cable (disconnected) to pin #18 at ECU plug (disconnected): Continuity (Zero to max 3 Ohms)

For clarification purposes:

Measuring the center amplifier feed conductor to ground, not the outer sheilding conductor to ground, correct? As the center amp feed conductor connects to …

Then on.this:

This would be measuring the resistance of the amplifer circuit (amplifier itself and the circuit in the ECU) through the ECU and the amplifier to some internal circuit point, possibly using ground as the retun conductor being measured?

What should one measure Pin #18 to ground?

What should one measure amp cable, at ECU connector, to ground?

yes of course

You just want to see if the cable is intact.
Both ends should be disconnected.

No continuity. If there is continuity it means that the cable is damaged and shorted to the shield.

Okay, my first thought was incorrect, so, based on this:

You are not just disconnecting the amp cable from Pin 18, you are also disconnecting the amp cable from the amp … how are you measuring the continuity of the cable (if you are measuring from the ECU end to the amp end)? My test leads aren’t that long, I would need to get out my long test jumper set of about 15’-20’, to reach the amplifier end.

Do you also test the continuity of the sheilding ground? Same length of test leads testing issue.

[quote=“JerryPeck, post:51, topic:364128”]
My test leads aren’t that long,

Any cable will do…
I don’t remember if the shielding ground is connected to both or just one end.
The problem is always the inside cable (very thin), it’s very hard for the shield to break.

Got it.

The inner conductor is the potential breakage point.

The test of it is end-to-end (ECU on boot to amplifier on engine, using long test jumpers.

I have some 18-2 (lamp cord) or 20-2 (speaker wire), I don’t remember which, that I’ve been using as long test jumpers for years. The identifier on one conductor (ridges or printing) makes it easy to keep polarity correct end to end when using them.

I have set the rotor to pickup at 0.15MM .OO6 would you say that this is ok I was told that anything between 0.10 and 0.15 is acceptable your view please.
All the other items that you mention have been checked and found to be operating correctly. Any furthher comments ? Clive

I was given this little trick to check continuity, … wired test bulb in trunk one wire to positive on battery one wire to pin 18 , … multi meter to ignition amplifier negative to ground positive to braided wire to ECU continuity = +or- , 12v on multi meter…and bulb should light up. I have neither so that denotes that their is no continuity twixt amp & ECU . Regards Clive

So now having carried out a myriad of tests to identify the reason that my injectors are not squirting fuel all of which returned positive results except one.
The one returning a negative result was the continuity from ignition amplifier to ECU it seems that the shielded cable has a fault and requires replacing.
Any advice on what co-ax to use and how to connect to pin 18 at the ECU would be much appreciated my kindest regards to all for the advice and information given so far . Clive

I’m trying to follow this:

  • wired test bulb in trunk one wire to positive on battery (okay, good)

  • one wire to pin 18 (to pin 18 of the ECU or of the plug which goes to the ECU ?#1)

  • multi meter to ignition amplifier

    • negative to ground (okay)
    • positive to braided wire to ECU continuity (the braided wire is ground, so checking continuity - got it)
    • = +or- , 12v on multi meter (no, checking continuity is not voltage, so you will not get voltage there … before checking continuity always check for voltage first - which you did - and if no voltage - there was none - then switch meter to ohms for continuity … all this part is doing is, as you said, checking continuity of the grounded braided shield … unless my mind is not thinking properly this morning - which is possible)
  • and bulb should light up (now you are back to voltage, not continuity, so I am again missing something)

Will others help try to explain the above to me as I must be missing something, or maybe it depends on the answers my my “?#1” ?

If the to this: “one wire to pin 18 (to pin 18 of the ECU or of the plug which goes to the ECU ?#1)” … is ‘to pin 18 of the plug’ (i.e., not to pin 18 of the ECU) … and that wire goes to the amplifier positive … I hope that wire was disconnected from the amplifier as you are using this as the ground wire for the test light,

Or … am I totally spinning out of control and I need to regain and stabilize my view of the horizon?

You are not out of control.

The instructions were to proceed in the fashion as described and to apply +12v via a test lamp to Ecu Plug, Pin-18 and have the white wire at the amplifier disconnected and see if there was +12v at that point, having been fed from the test lamp.
Even a low wattage test lamp will work, as both lamps will share the current. It’s arguably a better test as it loads the wire.

I think Clive may have connected to the braided shield, not the white wire core.

I’m not quite sure whether you have connected to the braided white wire inner core, or the braid itself. The braid is just a shield an isn’t the signal carrier.

If you have connected to the shield go back and redo the test, connected to the core.
If you connected to the core, it appears the wire is indeed broken.

I’ve not done one of these, nor have the specs, but I would think that should be fine.
The closer the pickup is to the rotor the greater the Ac voltage pulses will be, but there is a risk of collision.
0.15mm is a pretty fine air gap.

To the plug as it is the cable that is being tested it is of little consequence if it is ohms or voltage flowing through the cable it is the integrity of the cable from ignition amp to ECU plug that I am looking at if volt’s flow the line must be intact. In fact you complete the circuit with the multi meter sending the negative to ground. You are not spinning out of control I just do not explain things to well.
Sit down with a tube and relax…regards clive