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How does a Tacho work:
Ign volts to one side
Other side is a "make and break" (pulse) from the -ve of the coil.
With the Tacho -ve wire unplugged from the coil, there WILL BE 12V in that wire, "looking for earth to operate the Tacho".
VERY SIMPLISTIC OF COURSE, but [lease read on.
That ECU is a Tacho type device, well the circuitry inside for Injector activation is. SOOOOO, that White (Shielded) wire has 12V in it, and is "looking for Earth", which is via the Amp terminal, same terminal used by the Tacho.
That White Blob has 2 resistors inside, One for the Tacho, One for the ECU. If the Tacho resistor blows, dead Tacho. If the ECU resistor blows, dead ECU Injector circuit.
My suggestion, and I have not done this, just thinking outside my cage.
Unplug that Dreaded wire, attach the Volt meter, Analogue if you have one. (Or the test light) Other meter lead to earth, crank the engine, and note the pulse, or lack of. This will confirm IF the resistor related inside that Blob is good or bad. I have never had a resistor issue, but people do report them failing.
GREG and GRANT:
I went out and bought a Cheapo Analog Voltmeter from a big box store just in case the Analog meter I had was faulty. I hadn't used it in about 15 years and the battery inside was all corroded. I cleaned it up and it worked but I was not sure how correct it was until I bought the new one. Now I have 2 working Analog Voltmeters.
No luck with the tests Grant recommended.
All test were performed with the key on or cranking.
1. Test Light: Even though I have an Ignition Spark (which tells me that the field is collapsing within the coil) when I connect the test light to the - side of the coil, cranking the engine, the test light just stays lit with a very faint flicker (almost unnoticeable).
2. Reconnected W/B wire at the - side of the coil. I disconnected the dreaded wire from the Amp and connected the test light at the dreaded wire plug coming out of the Amp. The test light does not light up
3. Connect Analog meter to the plug I see battery voltage. Cranking the engine the needle just drops to 8 volts but does not flicker.
4. Connected the Analog meter to the negative side of coil I see battery voltage. Cranking the engine the needle just drops to 8 volts but does not flicker. KEY ON: meter connected to the - side of coil, Black dot on meter is my mark.
This is the same reading I get when connected to the dreaded wire plug coming out of amp Not clear. but the reading drops to 8v at the - side of coil and dreaded wire plug coming from the amp when cranking the engine. Needle does not move during cranking mode
Result: Both tests are inconclusive. Back to square 1. STOP: Let's leave all of the EFI stuff on hold UNTIL..... I think that I am seeing some issues that I must resolve before I proceed any further.
1. Ignition Spark is weak (Yellow) Car has new Cap, rotor, spark plug wires and spark plugs.
2. Voltage drop on - side of coil. + side = Battery voltage; - side = 8 volts. I will replace both coils.
Coils look good: Primary Coil Resistance = 1.5 ohms.
Secondary Coil Resistance = 1.5 ohms.
Both coils connected = 00.9 ohms. Why would the voltage drop from battery voltage on the positive side of the coil to 8 volts on the negative side of the coil during cranking? I have a battery charger connected and the reading at the positive side of the coil with the key on is 13.9 volts. That's a drop of almost 6 volts.
Distributor Pick up coil Resistance = 3.89 ohms. Is this good?
Air Gap = Unknown. I need to get a plastic feeler gauge.
AB14 Amplifier:
Module = New
Resistance readings from W/B wire to Dreaded wire plug = 6.95 ohms
" " " W/B wire to Tach plug = 10.06 ohms.
I think that the above readings are within Specs (Grant)
The 1 other thing I checked was the integrity of the dreaded wire shield.
The center wire has continuity to Pin 18.
The shield has continuity to ground
No shorts to ground with the center conductor.
Inside the Amp is that Condensor looking thing screwed to one corner, Remove it, Bin it, they leak to earth and reek havoc.
A Yellow Spark is not good, as you know. That Condensor can cause that.
Clutching at straws:
The engine Earth strap/s are GOOD, or there is a dedicated Engine to Chassis Earth cable fitted??
Earth cable bundle alongside the Battery, They Earth all sorts of items, including the ECU innards.
When you go to "crank" what is Volt drop at the Coil +ve?
Inside the Amp is that Condensor looking thing screwed to one corner, Remove it, Bin it, they leak to earth and reek havoc.
A Yellow Spark is not good, as you know. That Condensor can cause that.
Clutching at straws:
The engine Earth strap/s are GOOD, or there is a dedicated Engine to Chassis Earth cable fitted??
Earth cable bundle alongside the Battery, They Earth all sorts of items, including the ECU innards.
When you go to "crank" what is Volt drop at the Coil +ve?
More thoughts later, things to do now.
I been reading along with this, way out of my range of understanding (85) BUT, I was also going to suggest cleaning up grounds, especially the ones in the boot near the battery... Seems like a neglected area of the world. Then, all ground points, too. It really helps.
Grant: Voltage at + side of coil... KEY ON = 12.37 V; Engine cranking = 10.65 V = drop of 1.72 V. Too much?Greg: You had recommended replacing the coils earlier in the post but I was of the opinion that an impedance of 1.6 ohms was good enough to get the car running. Stubborn me. Kirby Palm and other posts say the impedance should be 1.2 ohms. Going shopping for new ones today.
What are you all using to adjust the Air Gap? What are the specs? I just eyeballed it when I put it back together after I serviced the centrifugal weights.
Jay: I have cleaned every ground point I could find. Especially those by the battery. I am going to add a 2nd ground from the engine to the chassis today.
Even though this car is kicking my butt (1st time working on a V12), I am forever optimistic. I have decided to go back and rework each piece of the system individually. Sometimes I tend to get ahead of myself and together with brain farts.............;.OH WELL!!!!
Sanchez
The pickup/starwheel air gap is not adjustable on the HE Lucas dizzy. Even though a weak spark, the thing was firing, so decent coils plus good clean connectors should do it.
Have you found where the secondary coil is? Do test the loom from the secondary coil to the coil by the dizzy for continuity, and be sure to fit new Lucar connectors.
My view on the V12 is well known - it is just not worth skimping on renewing the bits of a system. On a car of this age, there is NEVER just one thing to put right and "then it will be fine". The cash cost of doing a system properly is infinitely less grief-inducing than the emotional cost of the thing not working reliably, or not working at all, or just working and then failing. These are reliable cars once put right. I have done over 100,000 miles in mine.
Last edited by Greg in France; 10-08-2021 at 10:49 AM.
Greg: Yes, I am replacing both coils. The loom from the coil up front was the most pliable wires I found on this car in the engine bay Continuity check on those wires check out good.
The 4 wires coming out of the Amp are very brittle . Inside the Amp they are a lot more flexible.
This is just a thought. The 4 wires exit the Amp via a molded piece. Can I cut the wires right behind the molded piece and splice some new wire in? See photo (Top Circle 1)
The cash cost of doing a system properly is infinitely less grief-inducing than the emotional cost of the thing not working reliably, or not working at all, or just working and then failing.
Amen brother - how many have caused their own grief and blamed the car ?
All of the aftermarket coils available have an impedance of 1.5 ohms.
The Jaguar parts dealers want $90+ for each coil and they could not tell me what the impedance of their coils were. When I ask the question it was like " I dunno"
I do not think that a bottle coil should cost that much.
Where can I get coils with 1.2 ohm impedance. Can I get a brand and a supplier please?
Or should I go with this single coil: Jaguar Coil-Ignition
DAC-6093 Price:$79.95
Catch up, time zones suck, along with old age and Cov nonsense.
That voltage drop is borderline, but should make it go bang.
The ignition switch electrical switch needs attention, your call now or later.
I also fit a Relay in that White wire to the coil. Mine are all under the dash, near the switch, as I simply wanted NO MORE electrical stuff under the bonnet than absolutely needed. That will take a huge load OFF that switch (old that it is now), and give a much more steady voltage at that White wire.
I also fitted another relay for the Accessories circuit, that livened shiiiit up quite a bit.
That Jag single would be my suggestion now. Back in the day they were 4X that price, and I found an alternative. Fuelmiser CC215, but I am informed not easily found outside Aus.
"Eyeball" the ONLY measurement that matters. As long as the tip dont hit the other bit, move on.
While I am waiting for my parts to arrive from the vendor, I decided to service the AAV on the car.
On removal I saw that the AAV was in the open position and all yukky looking.
I decided to place the thermal bulb in boiling water to see whether the AAV was functional. Nothing happened.
I used Grants method to remove sleeve to access the piston and spring.
With the innards removed, I tested the thermal bulb in hot water and it did not move. It just stayed in the down position.
I am going to put it back together and install it on the car until I decide whether I want to eliminate it completely or look for a used working one.
Since it is non functional, when putting the AAV back together should I make sure that it is totally closed or totally open.
This way when I get my parts I will try to get the car running.
Thanks.
While I am waiting for my parts to arrive from the vendor, I decided to service the AAV on the car.
On removal I saw that the AAV was in the open position and all yukky looking.
I decided to place the thermal bulb in boiling water to see whether the AAV was functional. Nothing happened.
I used Grants method to remove sleeve to access the piston and spring.
With the innards removed, I tested the thermal bulb in hot water and it did not move. It just stayed in the down position.
I am going to put it back together and install it on the car until I decide whether I want to eliminate it completely or look for a used working one.
Since it is non functional, when putting the AAV back together should I make sure that it is totally closed or totally open.
This way when I get my parts I will try to get the car running.
Thanks.
Sanchez
I would have it closed; then you can regulate the tickover properly, using the screw. When starting, just holding the throttles open a touch with the pedal will substitute for the AAV. Just make sure the tickover bypass part of the AAV is not blocked
I ordered a new coil (DAC6093) yesterday. It won't get here before Thursday.
Yesterday, I was going through my parts bin and I found 2 coils. They both tested at 1.1-1.2 ohms.
I decided to try one of them this morning and I had a fat blue spark at the coil.
Given that, I installed the air boxes and using some starting fluid the engine fired up.
I will replace it with the new coil when it arrives.
Given the the engine has good ignition, I now have to focus on the EFI side of things.
I still have no injector pulse.
When I made the new harness for the injectors I did it the way Kirby suggested.
I have power at both injector terminals on all 12 injectors.
I still do not know if the pulse on the dreaded White wire is getting to the ECU.
The ECU is not sending the ground signal to the injectors.
I have 12 volts at the Power resistor. I have cleaned the terminal at the power resistor and even swapped it out for another one that I have.
How do I check the pulse signal from the AMP to the ECU? Can I run a regular piece of wire over the top of the car and splice it in the braided wire that goes to Pin 18?
How do I check the ground signal at the ECU?
I still have to study the circuits at the Power resistor to see which 4 terminals have power (should be the 4 pink/black wires)
Maybe the ECU is faulty?
$700 for a remanufactured 16CU( if available)
There are some 6CU available that cost less but the vendors cannot say whether they are good or not. They have not been tested.
Where do I go from here?
10-07-2021, 05:11 AM
