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#1 ECU on EFI cars

Posted: Wed Apr 10, 2019 1:27 pm
by MLBS3V12
Hi there,

I'm choosen to use an XJS EFI engine with the Jaguar ECU used on the donor car.
My question is : where is the best place to fit the ECU?
Do I have to cut all the wiring loom to get tthe ECU at the front , or is it better to keep all as it is and place the ECU in the boot ?
Thank you for your feedback.


#2 Re: ECU on EFI cars

Posted: Thu Apr 11, 2019 8:54 am
by jagwit
I mounted my Megasquirt ECU against the "ceiling" of the passenger footwell. I needed easy access to it with the comms cable from my PC.

IF you can find space in the boot, mount it there otherwise you will have to change some wiring (eg, to the fuel pump).

There is an unused plate on the passenger side where the steering collumn would pass through for LHD/RHD as required. I made holes through that plate to pass wiring and AC pipes through. That plate is easily made or replaced for originality. Perhaps you can use that too?

#3 Re: ECU on EFI cars

Posted: Thu Apr 11, 2019 2:03 pm
by MLBS3V12
Thank you Philip,

I hesitate between the 2 solutions.
The place exists in the Boot as I'm going to use an immerge fuel pump.
But harness from the XJS is large and I m afraid to get it visible all along of the body panel. Further more, I ll have to add large wires because the battery in the XJS is also in the boot. This means that I've to get additionnal large ones on an already thick harness.
I think I'm going to follow your proposition, reduce the harness and place the ECU on the passanger side. :hammerdrill:



#4 Re: ECU on EFI cars

Posted: Thu Apr 11, 2019 5:55 pm
by MarekH
Dear Michel,

The harness you are proposing to use assumes that the battery is in the boot and so you will need to adapt it for a battery in the engine bay. To put it in the boot without putting a bulge into the carpet or into the inner sill, you'll have to be very creative and probably run the loom down the left hand sill inside the car, or split it, as the right side already has white wire fuel pump wiring and the left has black/white rear window loom on top of the rear light wiring.

The downside of this solution is that you are buying into semi-life expired mid-1980s technology and the engine bay harness is almost certainly brittle by now. It also doesn't give you any control over spark timing or let you datalog the car's operation in real time or let you reprogramme the ECU. It also commits you to using the old idle valve, rather than new electric ones and you'll have to somehow plumb the heater matrix into the water rails as the xjs idle valve is on the same side as the heater box - i.e. they'll clash with each other.

The XJS swirl pot is probably quite rusty by now. I did briefly run a swirl pot in the corner of the boot behind the aerial, using the twin SU pump as a lift pump and then the Lucas FI pump to feed the engine bay from there. This worked fine when on petrol and will work fine for you, but I had to switch to an in-tank pump when I fitted LPG (autogas) as the recirculating unused petrol temperature when running on autogas killed the Lucas 2FP pumps. You won't have that problem, as your fuel pump will always be topped up by cool fuel from the main tank no matter how you arrange your swirl pot plumbing.

I still have the custom made swirl pot if you want to adopt the twin pump solution.
You can always search and look for pictures on the old photo albums of the website that might help you, should you want to. Both Philip and I have posted there.

kind regards

#5 Re: ECU on EFI cars

Posted: Wed Apr 24, 2019 4:58 am
by MLBS3V12
Thank you both for your return. I will continue to think to what sounds to be the best solution for me.
I've seen on the last S3 V12 restaured by E Type UK that the ECU they use is placed under the sit. A third way to be concidered.
For the fuel, I've planed to use the same kind of solution Philip did on its own S3.
Marek, the harness I've got with the engine sounds in a very condition except the injector part. All the wire have to be changed.


#6 Re: ECU on EFI cars

Posted: Sat May 11, 2019 2:19 pm
by MLBS3V12
Hi there
Finally after thinking and get an oportunity, I ve purchased a K6 Emerald ECU to get a fresher solution to manage both injection and ignition.
It will replace the 2 ECUs from the donnor XJS I ve got with the v12.
Because I get it from a guy on Ebay, It comes with a Lotus map.... A few work to do soon.

#7 Re: ECU on EFI cars

Posted: Sat May 11, 2019 4:48 pm
by jagwit
I suggest you get the car running with original ECU.

DO NOT UNDERESTIMATE the complexity of tuning an engine. If you have not done so before, don't even try. Take it to someone who knows how to do it.

#8 Re: ECU on EFI cars

Posted: Sun May 12, 2019 12:02 am
by MLBS3V12
jagwit wrote:
Sat May 11, 2019 4:48 pm
I suggest you get the car running with original ECU.

DO NOT UNDERESTIMATE the complexity of tuning an engine. If you have not done so before, don't even try. Take it to someone who knows how to do it.
I do not underestiate the job at all. I've read lot of data with the Megasquirt experience from many project and yours particularly.
The fact is that I dont want to start from scratch. This is why I compte on the positive feedback from Emerald as they can pre-map the ECU.


#9 Re: ECU on EFI cars

Posted: Sun May 12, 2019 5:57 am
by jagwit

I see that the Emerald K6 can only handle high impedance injectors (14 - 16 ohm). This is normal.

The jag injectors are low impedance.

In the FAQ of Emerald's web site they say that one can run low impedance injectors with K6 using ballast resistors. This is only partially correct. Using ballast resistors is OK for racing applications but its NOT GOOD for road applications where the engine will spend lots of time idling and on light throttle, both of which requires short pulse widths where ballast resistors DO NOT WORK WELL.

Solutions would be to either change your injectors to high impedance, or you will need "peak and hold" injector drivers from which will make wiring quite a bit more messy.

#10 Re: ECU on EFI cars

Posted: Sun May 12, 2019 8:40 am
by MarekH

You aren't starting from scratch; you are starting with an ECU which has hardware and software which is wired up for a totally different engined car. This may well be a worse starting point than with a blank Megasquirt ("MS"), as the MS has very clear instructions as to how to go from zero to a fully tuned car.

I'd say 80% of the work going forwards is the same whichever system you use, but to get to your destination, you have to understand where you are starting from first and you have chosen to start by shoehorning a Lotus into a Jaguar. To go forwards, you'll need to know how the Emerald runs a four cylinder Lotus first, then how to adapt a wiring harness for the wrong number of different types of injector and the wrong idle valve into the wrong car. It is very worrying that Philip is suggesting that your choice of ECU may not be well suited for this project without substantial further upgrade. A basic MS V3.0 board running MS2extra software is a proven solution for a Jaguar v12.

Basing your purchase decision because of worrying about how to tune the car is akin to worrying about the colour of the wallpaper when you still have no roof on the house. In your case, you are purchasing the second storey of a house which doesn't yet have any foundations. Yes it can be done, it'll be so much easier to just copy one of the four or five people who have already done this the easier way before you.

1. You first need to construct the hardware to get a reliable crank signal into the ECU.
2. Then you need to make a new harness compatible with all of the other components.
3. You then need to make the car start.
4. Then you can worry about the fueling - that'll be the really easy compared to 1 to 3.

For a good basic overview of the topic, take a look at Roger Bywater's website as to how the Lucas ignition and fueling work on our Jaguar cars.

Good luck
kind regards

#11 Re: ECU on EFI cars

Posted: Sun May 12, 2019 10:05 pm
by Barry
I can only talk about my own car which has a new 6.0 litre XJS engine. The ignition is based on the original 16CU Lucas system but has an AJ6 Engineering ECU fitted in the boot ceiling panel panel forward of the OTS boot lid. The ECU is supplied by Roger Bywater, who owns AJ6. I also have his High Torque TT throttle bodies and exhaust. Rogers web site is most helpful for anyone wanting to fit fuel injection to an E-type. In fact you will see my actual engine at the head of his article on EFI for E’s. Ring Roger for more information, as he was an original engineer who worked on V12 development at Jaguar. By the way, my engine pushes out about 400bhp.

#12 Re: ECU on EFI cars

Posted: Mon May 13, 2019 8:07 am
by MarekH
There is a wide continuum between "pay someone else for everything and get them to fit an old retuned ECU from the 1980s" to "I'll read up and then design and build my own gear" and Michel has chosen to be somewhere in the middle. There is nothing wrong in principle with what he is doing and I can't see any reason why it won't work out fine. It's just not the easiest starting point for the simple reason that no one here has experience of an Emerald K6 on a v12, whilst the huge pool of knowledge in the online Megasquirt community will not be available to him. The best bet is to simply read all of the Megasquirt "how to" guides and translate that knowledge across to the relevant K6 needs.

The only advantage I can see in the Emerald is the quality of the loom connector on the side of the box. There are many disadvantages everywhere else. A prebuilt MS3pro or MS3gold box would have had all of the pluses and none of the minuses, but that wasn't the chosen starting point. Ultimately, my bet is that this will stand or fall on the quality of the wiring loom he builds.

kind regards

#13 Re: ECU on EFI cars

Posted: Mon May 13, 2019 8:24 am
by jagwit
Dear Michel

With my previous posting, I only looked at Emerald from a technical viewpoint. This morning, I looked at its price and was shocked to see how expensive it was GBP714 (Euro827) !! By comparison, a Megasquirt-2 will be about USD350 (Euro312) - including a few extra bits and pieces.

MS-2 will not have any knock-on effects like upgrading injectors (and fuel rail) or the additional peak and hold electronics which makes the Emerald solution even more expensive.

Michel, you were on a good path planning to use the original ECU. With all my EFI conversions, I always found that getting EFI fuel supply sorted (never mind EFI itself) was a substantial challenge in itself. I now am of opinion that you made an error purchasing the Emerald.

I would encourage you to return the Emerald and either:
1) Continue with the OEM ECU and ignition (which will be challenging already);
2) Or go the MS-2 route – but using the distributor so that you can use a single ignition output on the MS-2, again to keep things “simple”.

If you do go the MS-2 route, I would further suggest that you do the EFI conversion in phases:
1) first get the car running again in standard configuration – with carbs and dissy – just to get it running again;
2) Then, implement MS-2, running off the crank trigger but controlling only ignition with a single coil output, a very low impedance coil (or using the original dual coils from an HE) and the distributor but still running on carbs; Ignition only will already present a massive learning curve but at least you will not be faced with issues on BOTH ignition and fuelling sides. Then, once you have ignition under control, you can move to fuelling.
3) Last phase would be to implement EFI, ; This means you can use the maps I (or Marek ??) can provide with support from us both (I presume) and the MS forum if need be.

Michel, allow me to add two more thoughts :
IMHO, the V12 E-type’s most urgent upgrade is from the outdated OPUS ignition system to a modern ignition system. A mapped ignition system is by far, 1st prize. Second to that is an overdrive transmission (again, my opinion!!) – NOT EFI.

I did the an EFI conversion on my 1st E-type (the OTS). At this time I did not understand carbs and did not care to either. After I had done that, the car was begging for an overdrive (and it had a 3.07 diff).

With my current E-Type, running Lumenition ignition (with vacuum advance) and VERY well tuned ZS-carbs (now that I understand carbs better), I again am faced with a car begging for overdrive because it is running so well that I am not at all motivated to do the EFI thing again.

Recently I “upgraded” the diff from 3.31 to 2.88 and this has improved matters HUGELY but even so, it can STILL do with an overdrive transmission.

All the above is intended to allow you a rethink of your project. Whilst our opinions may vary, I hope that the underlying reasons of those opinions may equip you with an understanding that will allow you to formulate a solution that will WORK for YOU.

#14 Re: ECU on EFI cars

Posted: Mon May 13, 2019 12:21 pm
by politeperson
Well, it has already been purchased, so too late!

I am sure the K6 will be fine Michel. Leoni will email your a Jaguar V12 base map (for free) to get it running, if you ask her, I am sure. Just plug in a laptop and upload it to the ECU.

I have a wiring diagram I can email you for the general wiring loom if you pm me.

The Emerald software has the option for setting the ECU to fire twin coils for a V12.

They are pretty good at helping customers with technical queries.

So as Marek says, just get it installed and go from there. You will have to have it set up on a rolling road anyway I would guess. Emerald may have any you need in stock, they are not too expensive.


#15 Re: ECU on EFI cars

Posted: Mon May 13, 2019 9:24 pm
by Barry
I think what Marek is saying makes sense. This could end up being a bit hit and miss, and you spend money on a system that clearly doesn’t work. The electronics in all of this is a bit above my pay-grade, but it is not something for the faint hearted, and certainly only for someone who is an experienced expert.I hope it all works out for you, and I will read with interest.

#16 Re: ECU on EFI cars

Posted: Wed May 15, 2019 3:48 am
by MLBS3V12
Happy to see that the topic drains so many reaction and information.
As James said, the K6 is already purchased.
Even so I still have 3 ways to go ahead:
1)I’ve got the K6. I’ve been in touch with Leoni, and yes, I should get data from her with a map and help. I add about this ECU that 2 of the last V12 E type restored by Etype UK are equipped with this K6 ECU. This is something that has motivated me to get one. You can see below 2 different position for the K6 to be installed.



2)Sell back ( try to ) the K6 and go to Megasquirt solution. There are several adepts.
3)Sell back ( try to ) the K6 and use the original Jag ECUs. At least I've used them a few weeks ago to start the engine and It runs fine.
I will keep you informed on the solution which I finally decide to use as I will certainly need your advice and feedbacks.

#17 Re: ECU on EFI cars

Posted: Wed May 15, 2019 6:37 am
by MarekH
That is substantially different information to that which you have previously given.
Good luck with your project.

kind regards

#18 Re: ECU on EFI cars

Posted: Wed May 15, 2019 2:22 pm
by jagwit
MLBS3V12 wrote:
Wed May 15, 2019 3:48 am
I add about this ECU that 2 of the last V12 E type restored by Etype UK are equipped with this K6 ECU.
It should be said at the same time if the original low impedance injectors and fuel rail were used or high impedance injectors.

I say again. Using current limit resistors IS NOT a good solution for a road car.
REASON: they slow the time the injectors require to open, down. But even that is not the main problem. No two injectors are the EXACTLY the same. One way in which they differ is that they do not have THE SAME opening time. Current limit resisors also INCREASE the DIFFERENCES in opening times. This results in significant differences in fuel delivered by different injectors when small pulse widths are required (idle & light throttle). Then some cyls are running overly rich when others are running too lean = engine unhappy.

I'm not saying K6 is no good! I'm JUST pointing out that it does not handle low impedance injectors and I AM saying that if you want to use it, then please also fit high impedance injectors. Do not be tempted by the resistors approach. MS-3 and most other ECUs don't handle low z injectors which makes MS-2 somewhat unique.

#19 Re: ECU on EFI cars

Posted: Wed May 15, 2019 2:54 pm
by MLBS3V12
I ve got information on the differences between low an high z on the injectors.
I ve also found literature on the P&H management to be used to drive low z.
If i need to add P&H bords or change the 12 injectors....Damn I should have choose a Citroen 2cv to not have this kind of issues or a mover, it is time to use it
I continue the reflection anyway. :-)
Thank you Philip.

#20 Re: ECU on EFI cars

Posted: Wed May 22, 2019 1:12 pm
by lowact
Hello Michel. Exactly the same as you, I intended to use the Lucas 16CU ECU from my donor engine. After discussing with Roger Bywater I concluded that 80's tech was just too old, too primitive. I checked out the Emerald K6, also the latest Megasquirts, imo these also a bit dated. Instead I will be using an Adaptronic M6000. This will give me full sequential fuel, also full sequential direct fire ignition, plus other capabilities too numerous to mention here, check their website if interested. for the sync signal I will be using a HALL sensor retrofitted into the distributor in place of the mech and vac advance mechanisms, as per this website: ... uar-HE-V12.