XJ6 & XJ12 Series I, II & III 1968-1992

injection ampli double six V12 1979 (3CU)

 
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Old 10-12-2014, 12:06 PM
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Question injection ampli double six V12 1979 (3CU)

Hello,
Can anyone explain how 4 injector groups can be controlled by 2 wires and a ground. I add below a part of the diagram of the injection with ampli connections and wires from 3CU. I also added the injection ampli diagram on pg 2. If it was a digitally controlled system I could under stand how to manage with to wires but I thinks it is stll analog mode. Many thanks for yr help.
 
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Old 10-13-2014, 05:33 AM
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Oh my.

I have all that in one of the hundreds of books in the library from the good OLD days of sorting these damn things, and the brain is simply NOT retrieving anything right now.

I will go look tomorrow and when I find the answer I will post back. There are lots of books, and lots more pages of scribblings from the day to go thru, so be patient.
 

Last edited by Grant Francis; 10-13-2014 at 05:35 AM.
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Old 10-14-2014, 03:54 AM
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Found the info. Many more pages than I remember, but to answer the original question is all I will cover here.

The trigger board inside the distributor has 3 basic wires (the newer 4 wire unit has an ign 12v feed as the 4th wire), and the related is as follows:
Trigger #21 (OLG) goes to pin #21 of the ECU.
Trigger #22 (US) goes to pin #22 of the ECU.
Trigger #12 (YB) goes to pin #12 of the ECU, and pin #12 of the throttle switch.

Each time the magnet triggers the board switches there is a pulse to the ECU, which in turn triggers the injectors VIA the amp unit.

Pin #5 (KU) of the ECU goes to pin #12 of the amp unit.
Pin #4 (KG) of the ECU goes to pin #11 of the amp unit, and the EGR control uit (if fitted).
Pin #24 (KB) of the ECU is the "power up" supply FROM the main EFI relay (Item 312 in the diagram), and also "powers up" the EFI amp via pin #10, and that relay also powers up other related items.

How that analogue amp unit splits the injectors is the "smoke and mirrors" part. Obviously 4 banks of 3 injectors are triggered by 2 trigger board switches, which are activated by the passing of the rotor magnet at each rotation.

My understanding is that each reed switch fires 6 injectors, but the split, as I said, is unknoown by me.

I do not have a schematic of that amp, and have never needed one, as I have never seen one damaged electrically. It is one of the most robust items in the whole system.
 
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Old 10-14-2014, 11:18 AM
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Default still mystery indeed

Originally Posted by Grant Francis View Post
Found the info. Many more pages than I remember, but to answer the original question is all I will cover here.

The trigger board inside the distributor has 3 basic wires (the newer 4 wire unit has an ign 12v feed as the 4th wire), and the related is as follows:
Trigger #21 (OLG) goes to pin #21 of the ECU.
Trigger #22 (US) goes to pin #22 of the ECU.
Trigger #12 (YB) goes to pin #12 of the ECU, and pin #12 of the throttle switch.

Each time the magnet triggers the board switches there is a pulse to the ECU, which in turn triggers the injectors VIA the amp unit.

Pin #5 (KU) of the ECU goes to pin #12 of the amp unit.
Pin #4 (KG) of the ECU goes to pin #11 of the amp unit, and the EGR control uit (if fitted).
Pin #24 (KB) of the ECU is the "power up" supply FROM the main EFI relay (Item 312 in the diagram), and also "powers up" the EFI amp via pin #10, and that relay also powers up other related items.

How that analogue amp unit splits the injectors is the "smoke and mirrors" part. Obviously 4 banks of 3 injectors are triggered by 2 trigger board switches, which are activated by the passing of the rotor magnet at each rotation.

My understanding is that each reed switch fires 6 injectors, but the split, as I said, is unknoown by me.

I do not have a schematic of that amp, and have never needed one, as I have never seen one damaged electrically. It is one of the most robust items in the whole system.


Indeed this is exactly as my diagrams are showing. I included the internal diagram of the EFI at page 2 of my document at the start of this treat. Still I cannot understand how te ECU can fire at 4 different times with those 2 control wires (the driving in the ampli diagram is analog). You suggest that the ECU only sends two times a trigger pulse to the ampli and that this would trigger the injection of six cylinders. This would be a serious mistiming for an injection... and indeed it looks like that on the diagram of the EFI AMPLI. Strange group firing...
Thanks for helping to think!!
 
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Old 10-15-2014, 09:12 PM
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Yes, the injectors are seriously mistimed, or not really timed at all. On modern systems we time the injection with the opening of the intake valve. Not so with this system, the fuel charge basically waits in the intake port until it is time for that cylinders intake valve to open. It still results in better fuel distribution than most carburetor systems. This was pretty common in the early days of port fuel injection.
 
 
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