Hi everybody,
Ok i'm in the middle of a engine swap. Putting a 6.0l v-12 from a 1994 jaguar into a 1986 jaguar w/ 5.3l v-12. It's been a nightmare to say the least. I'm down to hopefully 1 last thing that must be figured out. And that is the while the motor has been upgraded I had to use the computer that came with the car and the 5.3l. It used to take the rpm signal right from the negative side of the coil run it thru a resistor to calm it down abit, and then right to the computer. My problem is that the 6.0l i put in has 2 coils instead of 1. So if i just go off a coil signal it'll only be half of what it needs to see.. And the signal that it would send out to the 6.0l computer would come from the ignition module instead of the coil negative. This Signal is a low voltage digital square wave signal not an analog 12v signal like the 5.3l uses.

I can think of a few things that would work but don't know exactly how to get there.
1. Double the analog signal off one of the negative sides of a coil.
2. Take both signals and somehow wall them off at the motor and combine them before they get to the computer.
3. Convert the digital low voltage signal to a 12 v analog signal.

There may be other ways that i havent thought of. These are the ones that seem achievable without a big cost to make work. It seems to me that #1 would be the best option. At least then I think the signal would be what it's looking for and from the coil negative.

I'm open to any suggestion that will work. This car must go away soon because I'm losing my ass on this job as it is and just can't afford to keep having a chunk of every week be spent trying to problem solve instead of just fixing cars. I don't get paid to problem solve at this level. My bad for taking on the project to begin with. But I was in need of something challenging at the time. After 35 years fixing cars it's easy to get burned out if something doesn't come along every once im awhile to light that spark again make it fun and challenging. But Every single part of this job has been a process of either modification or fabrication or just plain invent something to make it actually work.

Anyways sorry for the long winded Post. I'm at the final stage of months of work in between other work to keep the lights on. It's an absolutely beautiful car and to add to the stress of getting it done the owner of the car's wife is dying of terminal Brain cancer and really wants to drive in her car one more time while she can. So the weight of this damn job is starting to crush me please help if you can. And any and all prayers towards fulfilling this lady's wish are gladly accepted.

Thanks,
Michael Wood
Lead tech shop foreman,
Marzocchi Imports
Gilbert, Arizona

 

The coil signals are based on camshaftspeed which is half crank speed. So the simple fix is a nag pickup to read the crank speed,
Combining the two coil signals is a good idea, probably much simpler. Clean then up and then feed them to opposite inputs of an OR gate. Or just use two diodes for a diode OR gate. It can not get much simpler than that. You guessed right but then dropped it, combine the signals and it will work.

 

I'm a little confused.
Here you say:

while the motor has been upgraded I had to use the computer that came with the car and the 5.3l

But then:

And the signal that it would send out to the 6.0l computer

So you are using both computers?

 

I'm a little confused.
Here you say:
But then:
So you are using both computers?

No sorry the 6.0l computer would receive the digital signal from the ignition module, but I do not have this module. I'm tasked to some how get a signal the 5.3l computer can read to it.

 

The coil signals are based on camshaftspeed which is half crank speed. So the simple fix is a nag pickup to read the crank speed,
Combining the two coil signals is a good idea, probably much simpler. Clean then up and then feed them to opposite inputs of an OR gate. Or just use two diodes for a diode OR gate. It can not get much simpler than that. You guessed right but then dropped it, combine the signals and it will work.

Well my electronics experience is basically on rare occasions repairing obvious burnt circuits with all the same components that were burned. That's a far cry from creating a circuit for a specific task. But I can read a circuit and source out the necessary components and solder all exactly the way the circuit shows. By any chance would you mind drawing out your solution?

 

"" My bad for taking on the project to begin with. ""

We live and learn.
Pre ~2000 Jag stuff is bad enough, even for a routine repair.

Do You have Electrical-System PDFs / Manuals for both Engines that You could post here ?

Not having a working Tach doesn't seem like it should be
a total deal-breaker if the Car drives Ok otherwise.
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"" My bad for taking on the project to begin with. ""

We live and learn.
Pre ~2000 Jag stuff is bad enough, even for a routine repair.

Do You have Electrical-System PDFs / Manuals for both Engines that You could post here ?

Not having a working Tach doesn't seem like it should be
a total deal-breaker if the Car drives Ok otherwise.
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I could careless about the tach. But the fuel injection computer absolutely needs this signal to properly function. It won't fire a single injector until it knows the engine is turning.

 

I will see if I can access those diagrams from home when I get there.

 

Then since You are using an older Computer on a newer Engine,
You need to make the newer Engine put-out a Tach-Signal that simulates the old signal.

I'm guessing that You are going from
a newer 2-Distributor-Engine to a Single-Distributor-Engine-Computer.
Is this correct ?

This, of course, assumes that You absolutely know for a fact that all other
important Engine-Signals are going to be backwards-compatible as well.
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If there are the two signals at half RPM, then an OR gate will provide the sum of the frequencies and that is what you need. So either a CMOS or gate or a diode or gate will do exactly what was requested. Simple and cheap.

 

I sort of know what you are up against, I rebuilt an '85 XJS after a under-hood fire.
See post # 7,893.
https://forum.allaboutcircuits.com/threads/and-now-for-something-weird.124706/page-395#post-1707437

 

Then since You are using an older Computer on a newer Engine,
You need to make the newer Engine put-out a Tach-Signal that simulates the old signal.

I'm guessing that You are going from
a newer 2-Distributor-Engine to a Single-Distributor-Engine-Computer.
Is this correct ?

This, of course, assumes that You absolutely know for a fact that all other
important Engine-Signals are going to be backwards-compatible as well.
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i had to reread your post. and yes that's exactly what I'm doing.

Close I am going from a single distributor that does have 2 coils but they work together to basically add a second charging coil to take up the slack of a single coil trying to charge and dump 12 times in four strokes. that's charge and dump at 1000 rpm 6000 times in one minute. needless to say that's asking a lot of a coil to try and keep up.

so the solution was to use a single distributor but with 2 distinct layouts inside the cap. so now there are 2 active and separate coil circuits that each fire 6 cylinders .

Hence my problem the rpm signal for the fuel management computer came right off the coil negative thru a resistor and that's it. I just need 2 coil signals to add together without interfering with the other ones' primary task . seems simple enough.

There's plenty of coil signal adapters to go the other way. taking a analog signal and converting to digital. for a newer type of tach or whatever. there's just not much I can find out there that goes the opposite way.

I'm sure there are many in this forum that know exactly how to solve this Delema. I just need to convince one of them to draw it up and give me a parts list.

 

Pictures and Schematics please.
Text does very little to convey the actual situation.

I'm great at aftermarket-Fuel-Injection-Systems,
but when it comes to British stuff,
things just get down-right weird, really fast.

It really makes You wonder what they were thinking when they did that.
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OK, so it seems that the challenge is to feed the computer with a tach signal that fires once for each cylinder. Now if you have positive-going pulses from each system, then the solution will be to add them together into one string of positive-going pulses.
So for my third time I will suggest an "OR" gate function, This is based on my guess that t6here are never two pulses at the same instant, that must be recognized each separately. That is what an "OR" gate will do for you. AND at 60,000RPM, much faster thanpossible, that is still only 1000HZ, far within the range of cheap digital logic.

 

Why do you have have a signal from both distributors for a tacho function?
Why not just use one and let the electronics (or software) compensate for the the other?

 

A voltage amplifier is trivial, but you need to define exact signal inputs and outputs.

 

Has this not got a crank position sensor on the flywheel, if so could you remove the inductive sensor, mount a hall effect sensor with some extra wiring and see what output thats giving, if not correct what about a custom reluctor wheel bolted to the front pulley using again a 5 volt (crankshaft) hall effect sensor to give it the correct signal it needs ? or even rip off all the old ECU\s and use a programmable fuel and spark ECU that'll control everything

 

I’m wondering why you haven’t responded to MB2s suggestion to OR the two signals with diodes? He has patiently suggested this three.times in increasingly clarified ways.

And I’m wondering what you mean by a 12V analogue signal - surely this would be a square wave too, as anything like a sine wave would suggest an uncertain trigger timing point.

Maybe in addition to the diode OR gate you need an op amp gain stage to raise the signal to 12V?

Would it help if someone sketched a schematic with suggested component values? I believe Mister Bill would be more able than I to do this

 

The Thread-Starter hasn't responded for a week,
he may have moved-on.

Most Thread-Starters don't report end results.
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