Reverse XJ12 VIN with engine number

XJ
1

Hello

I am considering buying an XJ12 coupe which does not currently have a matching number engine; it has engine #7P61561HAZ , and it is not working properly, maybe because it does not have the adequate injection ECU for this engine
so my question is the following: how can I find the chassis/VIN number of the car initially equipped with this engine, and if not possible, how can I find the minimum info about the year and the fuel system (with/WO catalyst ?, 6CU or 16CU ? …) and right ECU reference (DAC 2596 ? DAC 3062 ? DAC 2597 ? DAC 3586 ?)

many thanks

2

My brief research shows the the “HE” V12, as installed in the XJ12 cars, began with engine number 7P45001. This would be mid-1981 calendar year

If I’m correct then your 7P61561 would be an early HE engine.

I think the “H” = high compression. Not sure what the “AZ” signifies.

As far as I know none of the high compression V12 were fitted with catalytic converters.

I’ll try to find my early-80s XJ12 parts catalog…which might provide some useful info.

Meanwhile, others will chime in

Cheers
DD

3

thanks Doug
this starts clarifying the engine caracteristics
the meaning of AZ in the decoder I used is “grade A piston and liners”
what I miss is the type of Lucas Digital-P ECU: 6CU or 16CU ?
and the right ref DAC 2596 ?
the power module seems the same for all versions : ref 251234, correct ?
it is very well documented here : https://jag-lovers.org/books/xj-s/07-FuelEFI.html albeit the info I quoted above

considering the production numbers of the V12 series 3:

Jaguar : 12.404
Daimler : 9.820

unless numbering of engines was regardless wether it’s a 6L or V12, which I doubt, engine 61561 is 16 thousands cars after 45001 dated sept 1981, so wouldn’t it rather be a “late” HE in the series 3 (1984-5 )?

4

You can use either the 6CU or the 16CU, both will work.
The 16CU is somewhat better.
What matters is HE or pre-HE, the Compression Ratio and O² Sensors or not.
Don’t worry too much about which DACXXXX version as long as it matches your engine.
CEI means Lucas Digital-P

Hope that helps.

V12 ECU

6CU Part Numbers and Applications
DAC1926 6CU 1980 pre-HE OPUS 9.0:1 O2 Sensors
DAC1936 6CU 1980 pre-HE OPUS 10.0:1 NO

DAC2596 6CU 1980 HE CEI 12.5:1 NO
DAC2597 6CU 1980 HE CEI 11.5:1 O2 Sensors

DAC3062 6CU 1981 HE CEI 12.5:1 NO
DAC3586 6CU HE CEI O2 Sensors

16CU Part Numbers and Applications
DAC4118 16CU 1985 HE CEI 11.5:1 O2 Sensors
DAC4119 16CU 1985 HE CEI 11.5:1 NO
DAC4478 16CU 1985 HE CEI 12.5:1 NO

DAC4585 16CU 1986 HE CEI 11.5:1 O2 Sensors
DAC4586 16CU 1986 HE CEI 12.5:1 NO

DAC6335 16CU 1989 HE CEI 11.5:1 O2 Sensors
DAC6336 16CU 1989 HE CEI 12.5:1 NO

DAC6337 16CU 1989 HE Marelli 11.5:1 O2 Sensors
DAC6338 16CU 1989 HE Marelli 11.5:1 NO

5

Great Aristides, merci beaucoup !
my engine is just decoded as “high compression ratio”, does this mean 12.5 ? or 11.5 ?

6

If you noticed at the above table, all 12.5:1 engines have no O² sensors.
I think they were destined for the European market.

So if yours has O² sensors it would be a 11.5:1

7

my engine comes from an Italian car, I presume there are no O2 sensors; they should be in the exhaust ?
thanks

8

That makes sense.

I was thinking 1600 cars rather than 16000, which is what happens when I post before coffee :slight_smile:

Cheers
DD

9

When fitted, the sensors where located in the “downpipes” …which themselves incorporated catalytic converters.

If you don’t presently have and/or don’t want cat converters and oxygen sensors just use an ECU calibrated for high comp, no sensors

Cheers
DD

10

that thanks Doug and Aristides
I had a chance to look at Nigel Thorley’s book “Original Jaguar XJ” and he mentions p88 that in oct 1986 a new oil flow system was fitted from engine 7P56372.
May 1989 saw another change from engine 7P.020703 (misprint should be 620703 ?) and in 1990 engines are from 7P63107;
so I guess my engine was made between end of 1987 and April 89 ;
as for compression ratio, it changed from 12.5 to 11.5 in feb 1990 (which also saw the generalization of catalytic converters , so mine should be 12.5:1

11

How did you reach to these conclusions Rolando?

I might be wrong, but as far as I know, by 1990 the only 5.3 V12 cars produced where XJ V12 for the Canadian market.
All other V12s (XJ40 and XJS) had the 6.0lt with the Marelli ignition.

Why don’t you post a photo of your engine?

12

If it has no Cats, yes it must be correct.

13

I think you’re a little early re 6.0 litre. At least as far as the XJS was concerned the adoption of the factory 6.0 litre was closer to 1993.

1 Like
14

XJS engines started with “8S” not “7P” right ?
and no 6.0 l engines were mounted on XJ12 I believe ?
pic of the engine

IMG_5311 (2).PNG
IMG_5311 (2).PNG744×925 71.8 KB

15

Eventual O2 sensors are screwed into the exhaust manifold, Rolando…

The O2/Lambda are emission control devises - the engine will run perfectly well without them…

Frank
xj6 85 Sov Europe (UK/NZ)

16

Yes, on the XJ40.

5.3 HE CEI Lucas Ignition.

17

Accordingly to Roger Bywater the standardization of the lower compression was earlier.

The change to Marelli ignition for the XJS included a change to the lower compression. This was during 1988 calendar year. According to Bywater all V12s were then built with the lower compression, even those for use in the Series III sedans with Lucas ignition.

Personally I trust Bywater more than Thorley, but that’s me :slight_smile:

In any case I think the “H” in your engine number is the best clue.

To clarify…

This is an engine swap scenario, so the question isn’t whether or not Rolando’s car has cats. The question is whether or not the donor car had cats.

Right!

Perfectly well but perhaps not optimally, if the car is fitted with an ECU designed for use with O2 sensors

Cheers
DD

1 Like
18

mmh…
so it will need further investigation to check if it is a 1990 11.5:1 or a 12.5:1987-9
or understand what suffix “H” really means by “high compression”

19

[‘Running perfectly’ is sort of in eyes (ears?) of the beholder, Doug…:slight_smile:

What I meant is that a non-functioning Lambda, like failed O2 sensor, will not prevent the engine from running. However, whether Lambda’ed ECUs has the same connections as non-Lambda and are interchangeable is outside my ken…:slight_smile:

The Lambda is a refinement of mixture - bringing it to Lambda=1; compensating for fuel adjustment faults, and to some extent fuelling errors (within reason). As excess fuel may damage catalytic converters, it serves a valid purpose - and helps the environment even if cats are not fitted

Bearing in mind that the Lambda does not work until the O2 sensor reaches 400C - and is not active during pedal movement/acceleration.

Frank
xj6 85 Sov Europe (UKNZ)

20

I’m sure an archives search will reveal some useful info

Cheers
DD