EU vs US spec Marelli Period FI ECU question

Hey everyone! I made the mistake of selling my US Marelli FI ECU thinking I would never need it but I changed my mind and decided to get the engine running with the OEM stuff. What I want to know is, is there any reason I couldn’t hookup an EU spec Marelli ECU to a US engine? I am deleting all of the smog stuff including the catalytic converters and am making an all-new wiring harness that is thinned down so no worries about wiring or anything like that. I just wanted to know if the tune is a little “hotter” on the EU version seeing as emissions were not as strict and if it is was there any difference between the EU and US spec engines in 1990+ like compression ratios? The reason I am asking as I might be able to snatch an EU spec one cheaper than the US version.


I use a Euro/UK spec ECU on my USA V12 with no problems. I have a Lucas engine, though. Can’t be 100% sure about a Marelli V12 but I suspect it would be OK

As far as I know compression ratio was standardized at 11.5 for all markets when the Marelli system was introduced…including the Series III V12 sedans, which continued to use the Lucas system.


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Ok cool, do you know if there is any difference in the tune? does it feel more powerful or no?

Marelli is the ignition system. There is a separate ECU for the fueling, which is Lucas.
There are small differences between markets, but almost all FI computers use lambda-feedback.
There are very, very few that do not – they run on the factory maps – real unicorns.

I know I was just trying to make it easier for people to know which years I was talking about. I wonder though if there is much difference between the timing curve of the EU and US Marelli unit. does anyone know if they are digital ECU’s or still analog?

I am sorry if I came across as obtuse, but the title of the thread says “Marelli FI ECU”

No worries you didn’t, and you are right now that I look at what i wrote :laughing:

Changed it now :slight_smile:

So, you sold your Marelli box?

EU/US version of the ignition controller for the 6.0L (my engine) is the same:
DBC12473 or DAC11511

For the 5.3L, there are several variants,




My guess is that the timing maps are slightly different due to the availability of different fuels.

Nothing “digital”, old school stuff

I still have the Marelli Ignition ECU that goes in the passenger footwell but I sold the Fuel injection ECU.

Good to know I’ll just use my one then instead of trying to match it to a EU spec if there is only a slight difference due to fuel octane availability.

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The 36CU Lucas FI ECU, used in the 6.0L V12 is nearly impossible to find.

Good luck if this is what you are after (the choices for the fueling of the 5.3L V12 beast are less limited)

Thankfully I have a 5.3 out of a 1990 XJS so I just need a 16CU. But speaking of 36CU I see a couple on ebay right now for about 200-250 Pounds

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That’s not too bad, but, I don’t recognize the p/n for the XJS options given here.

This probably is from a XJ12 and may not work properly on the XJS. Only Roger Bywater would know…

There are a few minor differences in the Marelli ECUs per year, but seem to do mostly with choice of input type (temperature). I would assume there are some programmatic differences too given the expected input.

AFAIK pinouts were the same, but I haven’t looked closely:




1994 (I don’t have 93’)


As you can see, the most prominent swap was to use Intake Air Temp instead of water temp on the later cars… which is… strange… I guess the 36CU handled cold starts better? - and some TCM communication mostly dealing with retard request/acknowledge signals.

~Paul K.

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Another one here:

Thank you! I was too lazy to try and find all of the other years.

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And another but its an bid auction so you might be able to snatch one for cheap if anyone need one.

My ECU got the “super enhanced” treatment from Roger Bywater before I installed it, so that skews any comparison


Electrical guide would disagree. They have it labelled as “digital ignition”

LOL. Only if the engineers and the marketing people were to talk to each other.
The Marelli ECU is a digital as the “Jaguar premium sound system” is premium.

Yes, they use a chip and somewhat primitive by today’s standard electronic means of communication between the Lucas ECU, the Marelli unit and the transmission control, but there is nothing that even remotely resembles a CAN bus on the XJS.