I am considering a winter project to renew my injector loom. The wires are OK, but the plastic connectors to the injectors are becoming brittle. The loom is now 23 years old.
I am considering the scheme shown in the attached diagram "Loom idea". The OEM system has eight wires at the plug, four for each bank. The wires to each bank operate as pairs. Each pair triggers three injectors. As shown in the diagram, one pair of wires sends current to, and earths (grounds) from, three injectors simultaneously. I am wondering if I could dispense with the need for joins in the injector loom and instead use the connector crimps as joiners.

What I need to know is HOW MANY AMPS a single injector draws at the peak, opening phase?
Then I can calculate the wire size required to operate three injectors and thus see if my idea is practical in view of the injector connector crimp size which would need to accept two wires.

As a separate matter, I also enclose a note I have written on how the system operates, for anyone who might find it useful, titled "Ignition EFI diagram and explanation".

 

This old post by warriors might help:
"The ECU is wired in Peak and Hold with outputs for Peak and separate outputs for hold which go through the resistor pack.

The injectors in the V12 are about 1.6ohms (R) each and are wired in parallel in bundles of 3 so the resistance is actually 0.53ohms and the current the ECU has to supply is 22.6amps now if the ECU had to supply this current for the time injectors were needed to be open then the heat generated would be significant.

The resistor pack is a current limiting device designed to limit current I=E/R" end quote

So I=12.5v/1.6 ohms = 7.8125 amps peak opening per injector at a nominal 12.5 V. Then the resistor pack kicks in and limits the current. Obviously, the peak current drastically increases in groups of 3 in parallel.
You also need to figure in the duty cycle, i.e. how long that peak is held at high RPM, to calculate equivalent constant amps on the wire.
You are talking about daisy chaining the injectors. So if one connection is bad at the injector plug at the start of the chain, all three injectors quit.

Jon

 

Connector crimps as joiners would require a significant connector capable of at least 3mm² - crimping it would be a real challenge - not impossible but a challenge, also the cable bundle going back to the resistor pack would be significant. I did try to join them at the injector itself but it was not successful. In the end I used 1mm² thin walled cable Example and where I obtained and simply joined in the harness - juice wasn't worth the squeeze - .

I got the junior power timer connectors also from there (the injector connectors) - don't ask me why they're called this I have no clue I also got the rubber boots and terminals at the same time, I already had the crimp tool. I encased by cables in braided sleeving. The four pin connectors I used are the superseal variety (you need male and female) are a fiddle so get spares to play with - again all purchased at same place. I disposed of the 'moulded' connectors and now each bank has a 4 pin plug. I think that you can actually do away with or even common the 12V+ as it is the 12V- that is switched. I elected to spread the potential points of failure to a per bank, per trio

 

Ben, two questions:

1. Would you confirm the amperage rating of the cable you used please, it says 16 amps for 1mm square cable on the site ?
2. How did you make the joins in the loom (e.g. betwen B1 and B3 etc), this aspect is what is worrying me the most?

Great diagram by the way!

Also did you know that the junior connectors in the photo on site you posted will not fit onto the injectors once they are in place as the fixing collars prevent their going into place?

The release bar (at the bottom of the pic) will foul the injector fixing collar.

 

Jon
Thanks for this. I have to say that 22 amps seems a HUGE current for the rather small diameter wires used OEM in the injector loom (for instance as they exit the multiplug their diameter is nothing like 12 AWG) which is the recommendation for 22 amps.
https://www.engineeringtoolbox.com/w...ges-d_419.html

What amperage wire would you recommend?

 

Why not just buy a new one from Barratts? . Life's to short. 😊😊

 

Because, Rex, I have plenty of that sort of time which is not money!

 

The cable I used was 16 amp, you could probably get away with 0.5mm² but that's getting closer to the limits and I always allow 50% on cables.

They've changed the timer - this image shows what I used. I thought I got them the same place but seems not - came from Altec Automotive





My fuel system when completed will be somewhat modified as I won't be using the Jaguar 'square' rail, I''ll be moving to larger independent rails no fuel cooler, and much better fuel regulation - following Mr TWR - I'm considering hardlining the AC return.

The rails will look something like the image below, they are currently in manufacture by the TWR crew. Relocating the resistor pack is an interesting idea that I almost wish I had done - keeps everything on the engine except the trigger signals from the ECU..

 

Current ratings for wire are for continuous current, an injector is very intermittent. A long opening time (thus current draw time) on an injector can be 0.008 seconds. Another way of looking at it, for much of the typical drive cycles that is seen in average service the duty cycle on the wire can be 10-15%.

The wire length is also short, and standard tables are assuming much longer wire runs, which in turn affect the current carrying capacity.