VEMS on a Jaguar V12

[SteveT44]

I've been chasing an intermittent ignition issue on a V12 Jaguar XJS.  Getting quite tired of throwing time and money at the issue.  Thought a VEMS type solution would be interesting.  Is anybody on this forum aware of a Jaguar V12 VEMS conversion?

Regards,

Steve Tyng

[rob@vems.co.uk]

I was talking to a Jag specialist about this very same install.
You'd need to run the engine as if it were two 6cylinder engines - are the cylinders paired in a way that will let you do that?
Also you'll be needing a crank trigger, 36-1 would be best.
Its possible that you'll be able to use the stock sensors, but quite often its better to replace with known good ones.

[GintsK]

I have a long term Jaguar V12 project.
Because of serious engine modifications and lack of two WBO2 our decision is to use two VEMS boards.
It will be in one enclosure and some sensors will be shared between ones.
"Both" engines will run in alpha-n. May be even ITBs in future!
Custom 36-1 at front. No cam-sync. 2 BSOSCH wasted spark coils.

Gints

[irishtwincam]

I was talking to a Jag specialist about this very same install.
You'd need to run the engine as if it were two 6cylinder engines - are the cylinders paired in a way that will let you do that?
Also you'll be needing a crank trigger, 36-1 would be best.
Its possible that you'll be able to use the stock sensors, but quite often its better to replace with known good ones.

Quick search says firing order is
1A-6B-5A-2B-3A-4B-6A-1B-2A-5B-4A-3B 
60degrees between firing events.
Would 2 ecus and programemd 120degrees between events work?
Surely youd get trigger errors?

Aerial view of engine with firing order

FRONT
1A(1)   1B(8 )
2A(9)   2B(4)
3A(5)   3B(12)
4A(11)   4B(6)
5A(3)   5B(10)
6A(7)   6B(2)
REAR

On a 4 cylinder engine with firing 1-3-4-2 and 2 coilpacks, you pair cylinders by alternating firing.
So first coil 1, second coil 3, first coil 4, second coil 2
1-4 coil 1
3-2 coil 2
Injectors fire in pairs, in sequence so injectors 1&3, 4&2

Nissans RB20DETs fire 153624 which corresponsed with Bank A top to bottom, kind of, and bank B bottom to top.
So nissan pairing on a straight 6 would be
1-6 coil 1
5-2 coil 2
3-4 coil 3
Injectors would be pair 1&5, 3&6, 2&4

Confirmed (in part) by a Nissanophile here:
[img]http://car-media.co.uk/images/Vehicle%20pics/wastedcoils.gif[img]


So applying the same logic to the V12
youd have
1A(1)  -   6A(7) coil 1
1B(8 )  -   6B(2) coil 2
5A(3)  -   2A(9) coil 3
5B(10)  -   2B(4) coil 4
3A(5)  -   4A(11) coil 5
3B(12) -   4B(6) coil 6
With one ECU providing ignition events for both banks.

Injection pairing would be
1A-6B
5A-2B
3A-4B
6A-1B
2A-5B
4A-3B

Somehow it reads backwards to a straight 6 re injector airing vs spark pairing.
But theres a gap between sparking cylinders on each banks.

You could run all 12 banks from 6 ignition outputs, or does vems only do 4?
BAH, I should get back to work

[rob@vems.co.uk]

VEMS will do upto 8 ignition outputs.

You could even go coil on plug and use external igniters driven in pairs...

[GintsK]

In fact V12 is two 6 inline engines. In this case nothing except imprecise throttle linkage and common crankshaft did not unit this engine in a single system.
Both banks have separate intakes, exhausts, cams...Even OE distributor for newer versions had two seaparate "floors" for each bank.

If looks to OE history of V12 - two separate ECUs is nothing special. Even common!

I did not say, that one VEMS unit can't deal with V12. But this is more compromise than solution.

Gints

[irishtwincam]

Did I work it all out right then?