Guys, just a side note.
For those who don't want to or can't do it, SNG offers injector wires with original connectors.
I know that the price is higher

SNG Fuel Injection Wiring Harness

 

The new loom works absolutely fine on the existing fuel rail and I shall now proceed to remove that rail and instal the refurbished one. A definite improvement in evenness of tickover for whatever reason!

BUT this was not without dramas. I decided to test that each plug on the loom when installed on the injectors and plugged into the car multiplug, showed live on the live side and not on the earth/ECU side. To do this I removed one plug from one injector at a time (ignition on, everything else properly plugged in) only to find that the disconnected plug showed LIVE on BOTH SIDES!

A degree of anxiety ensued... the Franco/Australia hotline was activated and the following tests done:

1. I removed the new loom and INVIDUALLY tested each circuit by making it live AND THEN while that one was live also testing ALL the other 23 wires (injector connector plug individual terminal to the multiplug prongs) to make sure no shorts etc. ALL GOOD !!
2. I then also tested the multiplug itself for shorts and all good.
3. Then I connected the loom onto the car plug but did NOT plug the connectors into the injectors; then ignition on, retested each circuit. ALL as one would expect: ie live on one injector plug terminal, nothing on the other.
4. Then I plugged in the connectors into the injectors (still loom plugged into the car, ignition on) and removed one injector plug (A1) and LOW and BEHOLD, BOTH terminals showed live!
5. So I got to thinking and next I tried the following: using the new loom I disconnected all three injector connectors in one three-injector batch ie I disconnected A1, A3 and A5; (these are all on the same circuit from the multiplug). Igniton still on, multiplug still connected to the car, LOW AND BEHOLD, only one terminal on each injector loom plug was live!
6. I then plugged the A1 plug into A1 injector (still ignition on, multiplug connected) and tested A3 and A5 loom plugs that were still disconnected. They showed live on BOTH terminals. I then disconnected A1 and all three again showed live on only one plug terminal.
7. From this I can only conclude that enough current somehow goes through an injector coil to make a test light illuminate even if only ONE of the three plugs in the batch is connected (ie is receiving current on the live side). Remember that each separate terminal of the injector plug is commonly wired to the corresponding terminal in other two plugs in the batch, on the live side and on the earth (ECU) side. So all the live terminals in a 3 injector batch are electrically connected, the same for the earth/ECU side.
8. I then repeated test stages 5 and 6 with the old loom that I had removed this morning, and it showed exactly the same results: ie if only one plug in an injector batch is connected, then the other two plugs will show live on each terminal. Remove the one attached plug from the injector and all three in the batch show only one terminal is live, as I would expect!

So I conclude that we who think we understand these cars pretty well have a lot to learn!

QUESTION for the electronics guys:

Can you explain in layman's terms how it is that a unactivated injector can flow current through it? Does the solenoid coil allow just enough for a test light but not enough to fire it, or is current always flowing through it until it gets to the ECU earth switching system so all I was doing was picking this up with my test light which went to earth and not understanding it?

 

And you found out, when ALL injectors were disconnected (the circuit was open) you saw Voltage (not current) on ONE side only.

This is normal. Think of current as when water is FLOWING through a pipe, not sitting still, and think of Voltage as water PRESSURE in that pipe (its an imperfect analogy, but it works). When you connected any one injector, which has a coil inside, the PRESSURE was available to see across the entirety of the piping, because there was a connection.

When the ECU provides a ground (a way for the water to flow back to earth/battery side ground) then you can think of it has having current flow, while the pressure drops, and work is done (activating a NOID light or Injector.) There are other things going on like inductance and reactance that resist these voltage and current changes but for purposes of this discussion we can ignore that ATM.

~PK

 

Ferrari Guy
Thank you for this explanation. Overnight I was thinking about it, and I realised that I was thinking of the injector as a switch, and thus wonderd why it was live on the open side. In fact it is not a switch and the eath side will always flow some voltage because the actual switch in this particular circuit is well downstream of the injector at the ECU.
So, to use your analogy and taking the garden hose sprinkler as the circuit, I was sticking a pin upstream of the closed off sprinkler, but downstream of a join (ie the injector) in the hose, and wondering why I was getting sprayed when the sprinkler itself was not sprinkling!

Am I right Sir?

 

Essentially, yes, but... here's where that current and voltage thing come into play. Movement of the flow would be current. So it's more like you were wondering why there was pressure (voltage), where you expected there to be no pressure, because there was no sprinkler spraying (sort of the assumption that they're a combined thing). Both the lack of pressure (no power/voltage) and lack of an opening (to allow flow) can both result in no current (water coming out of the sprinkler). Again -water and pressure, imperfect analogies, but they help.

So in the real water based world, when you put a pin in the hose, you opened a path to ground, so saw the water flow into your face, (and a decrease in pressure slightly from that flow...)
In the circuit world, you've just measured that there is pressure. Nothing hit you in the face.

In an electrical circuit actual FLOW would bring the circuit area (closest to ground) to 0V on the ground side at the ECU with a voltage DROP occurring across where it is used (the injector and power resistors). In a closed (grounded) circuit, the sum of the voltages is zero, but there's 12V at the source. (Like water at the top of a water tower has potential to move to the ground, and can then move no further / do no more work, because there is no more potential energy) .. ok unless you move the ground lower - but that's another story.

I asked ChatGTP to help with this:

Key Concept:

In a closed circuit, the total voltage (pressure) provided by the battery (pump) is distributed across the components, and the sum of voltage drops equals zero. Voltage is still measurable at the battery terminals because the pump (battery) provides pressure.

Circuit Overview:

1. Pre-injector (between battery and injector):
   • The voltage here starts at 12V (full battery pressure) when the circuit is closed.
   • Drops occur across components downstream.
2. Between injector and power resistor:
   • Voltage (pressure) decreases after the injector because energy (voltage) is used to push current through it.
3. After power resistor (at the ECU switched ground):
   • Voltage drops further across the power resistor, eventually reaching 0V at the ECU ground point, completing the circuit.

1. Open Circuit (Faucet Closed):

• Pre-injector:
  • Voltage is 12V, as the circuit is incomplete, and no current flows.
  • Think of the pipe being pressurized but blocked at the faucet.
• Between injector and power resistor:
  • Voltage remains 12V because no current flows, so there’s no pressure drop across the components.
• After power resistor (ECU ground) (the other side of the open switch e.g. ground itself) (Note Chat GTP isn't quite getting you'd still see 12V at the pins of the ECU past the power resistor). Ground is still 0 of course past the controlling MOSFET switch.
  • Voltage is 0V because the faucet (ECU) is closed, preventing any water (current) flow to ground.

2. Closed Circuit (Faucet Open):

Now current flows, and voltage drops occur across each component.

Pre-injector:

• Voltage starts at 12V (full battery pressure).
• As current flows, the injector (low resistance) consumes some energy, causing a voltage drop proportional to the current.

Between injector and power resistor:

• After passing through the injector, the voltage drops.
• The remaining voltage is higher here than after the power resistor but lower than the starting voltage.
• The exact value depends on the injector resistance and current flow.

After power resistor (ECU ground):

• The voltage drops further across the power resistor (high resistance), leaving 0V at the ground point, where water (current) flows back into the water tank.

Voltage Drops in Action (Numerical Example):

Let’s calculate the approximate voltage drops:

• Battery Voltage (12V):
  • Total pressure to distribute.
• Injector (2.4Ω):
  • Current = I=VR≈122.4+6000≈0.002 AI = \frac{V}{R} \approx \frac{12}{2.4 + 6000} \approx 0.002 \, \text{A}I=RV​≈2.4+600012​≈0.002A.
  • Voltage Drop = V=IR≈0.002×2.4≈0.0048 VV = IR \approx 0.002 \times 2.4 \approx 0.0048 \, \text{V}V=IR≈0.002×2.4≈0.0048V.
• Power Resistor (6kΩ):
  • Voltage Drop = V=IR≈0.002×6000≈12 VV = IR \approx 0.002 \times 6000 \approx 12 \, \text{V}V=IR≈0.002×6000≈12V.

Summing Voltage Drops:

• Pre-injector: 12V.
• After injector: 12V - 0.0048V ≈ 11.9952V.
• After power resistor: 11.9952V - 11.9952V = 0V (at ground).

Water Analogy Summary (with Pressure Drops):

1. Open Circuit:
   • Water pressure is 12 psi everywhere upstream of the faucet (ECU), but no water flows, and there are no pressure drops.
2. Closed Circuit:
   • Water pressure starts at 12 psi.
   • The injector valve restricts flow slightly, reducing pressure after the valve by a tiny amount (~0.0048 psi). (Which is a fair amount of actual current / e.g. work, because there is so little voltage restriction)
   • The narrow pipe (power resistor) reduces pressure further, dropping it to 0 psi at the tank (ground).

Sum of Voltages is Zero:

• Voltage rises by 12V at the battery and drops across the components until reaching 0V at ground, ensuring the sum is zero in a completed circuit.
  
  ~PK
  
  Hopefully that didn't Muddy the "Waters" too much.

 

Now I know whenever I did wiring replacement,, it was ONE wire at a time, and think no more of it.

Awesome explanation, simple as opening a bottle of beer.

Speaking of which, YOUR SHOUT Greg.

 

I cleaned up the car loom to spliced-in injector loom multiplugs with contact cleaner and toothbrush on the male side (injector loom) and female side (car loom) as best I could, and also as mentioned above soaked them in lemon juice beforehand.

I retested them afterwards (still on the original injector rail, not on the refurbished one) and all good. In the meantime I had purchased a tiny tube of Deoxit D contact cleaner. This arrived a couple of days ago and I used it on the end of a Q-tip cotton bud to re-do the multiplug. Amazingly quite a bit of black crud came off on the Q-tips inspite of the contact cleaner and lemon juice treatment. See these links:
https://caig.com/product/deoxit-d100l-2c/

general link
https://caig.com/deoxit-d-series/

Anyway, as I was about to remove the old fuel rail this morning, I thought I better plug the multiplug together again and start the car to make sure all was working as it should be before removing the old rail. WELL, the car started INSTANTANEOUSLY !! It is minus 3°C in the garage (say 27°F) and the car had not been started for three days; but the thing started and purred over like it was fully warmed up! It normally takes a couple of seconds and it has the odd cough before all 12 catch when stone cold like this. But not today.

So I conclude that (a) Deoxit D works, and more importantly (b) cleaning the injector loom to car loom multiplug should be on everyone's annual V12 service list, along with the resistor pack. In fact it may well be that slightly rough running on startup and the odd miss when ticking over warm may be as much to do with the multiplug to the injectors as anything on the ignition side.

After this revelation I undid the clamps on the injectors and removed the old injector/rail assembly from the engine. It came off fine, and the flexibles from the rail to the injectors were pretty much perfect; no cracking, still very soft and flexible; a tribute to the guys in Luton England who redid them for me in about 2001.
BUT:
each injector has a large rubber seal round the bigger diameter under the clamp, and a much smaller on round the pintle. Each of these seal against the manifold in separate places. This smaller seal is ringed in red on this shot of my newly refurbished injectors:


These smaller seals fit into machined indentations in the manifold to provide a very tight seal between the pintle and the manifold, and all of them stayed in their indentations when I pulled out the rail/injector assembly. No bother here, I just hooked them out with a small pick.
But the important point is that these seals were pretty well shot, as shown in these photos:






The large seals under the clamps were as good a new, as were the flexibles carrying the fuel from the rail. The injectors, as mentioned, were refurbed 23 years ago and at least 60,000 miles ago. It is clear than my efforts to control under bonnet temps have worked pretty well; BUT the pintle seals quite clearly have a very hard time and I would say should be renewed every 10, or the latest every15 years.

There was also quite a bit of fine, hard, baked-on dusty deposit round the outer edge of the seal and on the machined indentation (bits of which are clearly shown in the photos), which I blasted away with brake cleaner and a screwdriver, which indicates how vital this pintle seal is to keep crud out of the inlet manifold,as this stuff had obviously been sucked into the seal edge over the years.
The seals had not gone hard, they just seemed to have started to crumble/give up all over their surface.

By the way, it is much easier to fit the injectors back in with this seal pushed into the manifold, rather than mounted on the pintle, so I removed them from the refurbed injectors and have pushed them into the manifold indents, ready for Tuesday morning when my copain (mate) comes round to help me fit the new rail.

 

Greg,

Great info! Particularly interesting that perhaps an increased resistance or impacted current flow might cause difficult starting on an original loom / plug? Will be interested to see if you have much improved starting once everything is back together.

Cheers

Paul

 

Well done there Greg.

Yes, those pintle seals work very hard.

About 10 years tops from my findings, BUT, we all replace the fuel hoses at about that time frame, do we not?

Spray a little Silicon Spray on those seals before pushing the Injector in, soooooo much easier, and the risk of seal damage is zero.

 

Guys
My friend Michel and I tried to fit the rebuilt manifold with the shorter hoses yesterday. IMPOSSIBLE. Short hoses a disastrous idea!

As shown in the attached PDF diagram, longer (as on OEM) hose lengths are needed because the width of the fuel rail (160mm) is substantially smaller than the width between the injector holes in the A and B bank manifolds (190mm) ie 32mm = 1 1/3 of an inch!. As a result there was just not enough "give" in the shortened hoses to enable the injectors to splay outward by 2/3rds of an inch each side to fit into the manifold.

I did not know this and found out the hard way yesterday, so my lovely short hose rebuilt manifold is being taken to bits and longer hoses fitted.

It turns out shorter hoses are a BAD idea!

In this attached pdf diagram, the red lines show the shorter hoses and the green lines the longer ones, which can bend sufficiently to accomodate the wider than fuel rail width between the manifolds. Photos of the old rail and injectors added here:

Shows the distinct outward splay of the injectors. The hole in the manifold is also angled to accept this angled insertion.

The bend required in the flexibles to make the ijectors fit to the manifold is very obvious in this photo

 

Greg,

That's a real shame if you can't the principle of shorter hoses to work! I'm sure you've considered it, but just a random idea:

- Is there any way you could slightly lever out each of the extrusions on the fuel rail to enable a wider reach when the short hoses are attached?

Paul

 

Thanks for the idea and encouragement. I think the only way would be to cut the fuel rail and weld in a widening piece, on the square rail and on the round crosspiece. As shown here in blue. I am tempted!

It would need about an inch welded in a shown in blue

Once the car is running I will discuss with my welding gurus and maybe sacrifice the spare one! I could test it using the old injectors which would be easy to swap in as a unit.

 

This morning I set about removing the stumps of the shortened hoses from the barbs on the injectors. I had cut the hoses between the rail and the injectors to free them off.

First I prised the Oetiker clips off with some pliers, not too bad. Then, taking one injector, I wrestled with some side snips to get the ferrules ripped off before at great length and effort getting the hose off without ruining the barbs.
Most painful and trying. Then I got the brain warmed up and remembered I had one of these:



Which has a hot knife attachment. Well, it cut through the rubber hose like the proverbial hot knife though butter, and after the cut, the pliers just pulled it off the barbs sideways and the ferrule came off on its own. Six injectors sorted on 5 minutes! I tell you, for anyone working on replacing injector hoses, this is the tip of the century!

Then I re-hosed six injectors with the OEM hose length of 52mm, then offered them up and clamped them in place without the rail being attached. You can see from this photo how angled inwards the injectors and their hoses are when clamped up properly:


Next I offered up the rail, and the rail spigots were OUTSIDE the injector hose tops - which is the opposite of what I expected. So I lopped 5mm off the hoses and offered up the rail again. Still the rail barbs OUTSIDE the hose tops. So I lopped the injector hoses down to 40mm overall length, and then offered up the rail. Things were just about perfect, allowing for the fact that the rail was not inserted into the hoses, just resting on the their tops:


Now, 40mm hose length is only 2mm longer than I had in my impossible to fit setup. So what changed and what do I deduce from this cockup?

1. The injectors HAVE to be fitted to the manifold and properly clamped in place without the rail being attached.
2. When this is done the rail can be quite easily pushed into place even with the OEM hoses cut down to 40mm from 52mm.
3. Then not forgetting the clamps (if they are being used) and the ferrules to be placed onto the hose first, the rail goes on with no bother, using one person each side to ensure the rail barbs locate properly into the hoses.

My mistake was clamping the injectors and hoses onto the rail; I think if I had fitted the injectors first, all would have been OK. Certainly at 40mm hose length it is. I now await some ferrules and pintle caps and I hope things will go together reasonably easily.

 

I have been considering a custom fuel rail using AN fittings something like this. Any feedback would be appreciated.

 

Greg,

Great perseverance! Well done! Looking forward to seeing a pic of the installed rail on the cut-down hoses.

Just as a matter of interest, if one is leaving the hoses at a standard length, is it still easier to do the install with the injectors already in the manifold, or is it easier to install the injectors on the rail first?

And thanks for the tip on the soldering iron. I've been worrying how to get those hoses off without damaging the delicate barbs!

Cheers

Paul

 

Yes Paul.

It is how I have always done it, without any thought of WHY.

Back before Forums and stuff, we just :did things; again, without thought that someone 30 odd years later might want to know HOW???.

A place for us Fossils after all.

I like Gregs "brain warmed up", what Brand was that liquid Greg?

 

Definitely install on the manifold first, whatever the hose length used.
As for the soldering iron, FYI previously I had tried out my electic one and it did not work. But the gas powered one, fantastic!

 

i thought of this as well. But one step further, use modern injectors and do away with all
the rubber hose. This would require the later intake manifold(which I happen to have in the garage)

 

I have the AJ6 High Torque manifolds and larger throttle bodies which I plan on keeping. I’m also considering the Mobeck distributor-less ignition so making a custom fuel rail just seems like a reasonable mod. Would love to fine a thread by someone that has already done this.

 

Guys
Time was found today to fix the rail onto the injectors.
Extremely straightforward: With Michel's help, and one of us each side, we placed the rail onto the tops of the flexibles (the injectors were already fixed in place) so that A 1-5 and B 1-5 's rail spigots were just engaged, not quite to the first barb, into the tops of the flexibles.

Then with one person on one side holding the rail in place so that side's spigots could not jump out, the other person using a hide hammer taped the rail home so the spigots were fully onto the barbs. Then the other side was tapped home.
I had remembered to fit the hose clamps onto the flexibles, and all that remained was to do them up.
A1 and B1's flexibles were then offered up and their longer hoses cut to length and fitted.

I pressurised the fuel rail to check for leaks before refitting the ignition stuff to the coil. All good. Then tried to start the car and NOTHING.

Then I remembered to fit the injector loom! THEN she started right up.

Interesting point: It takes quite a while for the injectors to fully purge the air. The car ticked over perfectly to begin with, but did not want to rev under no load, or pull in gear. We left it ticking over for 10 minutes and then all perfect. I have just finished a longish test run and all good.

Points for anyone considering doing this job:

• The best injector orientation configuration for a custom length injector loom for a pre-facelift HE engine loom is ALL injector plugs facing forward EXCEPT B1, which I refitted to face backwards. As I had to redo my injectors, they are now in this orientation. B1 faces rearwards because the offset nature of the heads (B bank being further forward than A bank) enables its loom to be tidier and out of the way.
• The flexibles were cut to 40mm long, which is 10 to 12 mm shorter than OEM. This gives better clearance between the rail and the bonnet at the front end of the rail. You often see witness marks in the bonnet cross-strengthener from A1 and B1 ferrules.
• Being winter I have not had a really hot start (say) 30 minutes after a hot stop, so I do not know for sure if hot starting will be easier (the main point of shorter flexibles) but my impression after a 20 minute wait, bonnet closed, is that it caught faster than before.
• For sure initial start from cold is quicker (but this may be because all the loom plugs were new, the injector prongs deoxited, and the same deoxit treatment given to the loom plug, the resistor pack plug and the TPS plug).
• The car runs noticeably smoother too, for whatever reason (probably as explained in the last point and also because the injectors had been cleaned).
• Because the injector barbs and the barbs on the rail had been cleaned and their sharp edges lightly sanded with 400 grit, I used Oetiker clamps on the injectors and fuel pipe clamps on the rail end (as these cannot be accessed easily by the Oetiker pliers when the rail is fitted to the injector flexibles). Therefore no ferrules were needed.
• The big plus for me is that the injector loom is 100% silicone insulated 18 AWG cable, well wrapped with three layers of protection, so cracking injector looms shorting out should be permanently prevented.

A few pics:


Offering up the rail


Front two injectors fitted after the back five each side have been fitted



Oetiker clamp on the injector, stainless fuel pipe clamp on the rail spigot


Front injector close-up


New loom being cable tied to the rail, NOT in the bottom of the V.


Combined loom wires wrapped together and cable tied in place.


Close-up of the spliced OEM injector loom plug connected to the car loom.

All tidied up (as far as is possible in a V12). The blue line is the secondary coil and the amplifier wires coming from the apron in front of the radiator stacks. The amp is moved there to keep it cool (a Grant Francis mod).
The other line shows the direction of the injector loom starting out from the front: