ECU on EFI cars

Talk about the E-Type Series 3
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MLBS3V12
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#1 ECU on EFI cars

Post by MLBS3V12 » Wed Apr 10, 2019 1:27 pm

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.

Michel
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Le chemin sera long!...

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jagwit
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#2 Re: ECU on EFI cars

Post by jagwit » Thu Apr 11, 2019 8:54 am

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?
Best Regards
Philip
71 E-type V12 Coupe,
80 XJS (EFI by Megasquirt & EDIS-6 + 5sp manual overdrive)
73 Jensen Interceptor
74 Interceptor (EFI by Megasquirt + overdrive 4sp auto)

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MLBS3V12
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#3 Re: ECU on EFI cars

Post by MLBS3V12 » Thu Apr 11, 2019 2:03 pm

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:

Cheers

Michel
Le chemin sera long!...

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MarekH
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#4 Re: ECU on EFI cars

Post by MarekH » Thu Apr 11, 2019 5:55 pm

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 jag-lovers.com website that might help you, should you want to. Both Philip and I have posted there.

kind regards
Marek

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#5 Re: ECU on EFI cars

Post by MLBS3V12 » Wed Apr 24, 2019 4:58 am

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.

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