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Jaguar XJ12 5.3
Jaguar XJ12 5.3

Chapter 15 of D-Jetronic article series by Dr-DJet describes specialties of Jaguar's D-Jetronic implementation in XJ12 and XJ-S

Well knowing that carburettors would not enable Jaguar to fufill coming US exhaust gas regulations, they asked AE Brico in Coventry to build an electronic injection system based on Bedix Corporation's Electrojector for them. But both unreliabilty of its prototype and the readiness of Bosch's solution and Bosch's patents let AE Brico close the project in 1970. So Jaguar suddenly had no solution and Bosch could only supply a product for 4, 6 and 8-cylinder engines. Limiting factor was the current that the Bosch 6-calinder ECU could supply to injection valves. So Jaguar asked Lucas to use Bosch D-Jetronic and extend it for 12-cyinder engines. That is why Lucas was asked to develop and extend the Bosch D-Jetronic (Oh my god lucas! British people make many jokes like "Why didn't the Germans bomb the Lucas plants during WWII? The Germans considered Lucas an ally. / Lucas is an acronym for Loose Unsoldered Connections and Splices.). That is why Jaguar launched its D-Jetronic in XJ12 and XJ-S late in 1975 when other manufacturers had already started to switch away from D-Jetronic. Jagur and Lucas continued with D-Jetronic until 1981 when they launched System-P..

15.1 ECU and amplifier

Jagaur ECUs are based on Bosch 6-cylinder ECUs. Changes are mainly in drivers for injection valves. These drivers are not present, only pre-amplifier signals for 2 injection groups are sent to Lucas amplifier via pin 4 (group 1) and pin 5 (group 5). The amplifier drives 6 injectors with each of these signals. Grouping of injectors is written below. Everything else in the ECU is like normal 6-cylinder Bosch ECUs. That is why the 5 different ECUs for Jaguar were also built by Bosch.and also brand labeled by Lucas. One ECU is only for Europe without full-load contact and the last one 0 280 001 025 is the only one with over-run shutoff capability. This means that you can read everything about your Lucas ECU in chapter 3 ECU and also use the list of usage and compatibility. Everything started with an early European and an early US/CAN version of the ECU. After that it gets complicated. First there is a common ECU for both Europe and the US. But ever stricter exhaust regulations in the US, Australia and especially California demanded 5 different ECUs till 1981 in total.

The Lucas 2PA injector amplifier uses 4 power transistors and 4 power resistors to drive 12 inecjtors, meaning 3 each. It has no logical functions and receives 2 triggers for 6 injectors each from ECUECUDefinition: ECU - short for engine control unit. An electronic device that controls engine operation and reads all sensors. Both in D-Jetronic and KE-Jetronic. In German it is called Steuergerät....
. Additionally it has a power and a ground connection. Poer transistors switch ground to injectors and  power resistors permanently supply 3.5 V to injectors. So failing 6 injectors can mean a missing trigger. 3 failing injectors mean a failing power transistor or power resistor.

Injection sequence is as follows:

Please log in to have a look at ECU and pressure sensor mapping to cars and year of make

15.2 MAP sensor

MAP sensors demonstrate a much clearer picture. There is an early and a late version of each the European and the US MAP sensor. European MAP sensors are of type 2. They have a full-load diaphragm that tends to tear as with all type 2 MAP sensors. USA/CAN cars have a type 3 MAP sensor. They don't break so easily but people to to detune them. So all statements in chapter 4 MAP sensor are vaild for Jaguar pressure sensors. Usage and compatibility is also documentsd in chapter 4.

15.3 Injectors

Jaguar injectors C45675 are the original green Bosch ones and have Lucas no. 5288036. But you can also use Bosch 0 280 150 035 or any other green Bosch D-Jetronic injector. Watch out for the rubber seals underneath the injectors and fuel hose leakage. Everything else in chapter 5 injectors.

15.4 Throttle switch

The  throttle switch is another original Bosch part with no. 0 280 120 046 or Lucas 184SA 30625A. It is a 5-pole version with full-load contact, no matter whether we have a European car with type 2 MAP sensor and full-load diaphragm or a US car with type 3  MAP sensor without diahpragm. US/CAN car ECUs evaluate the full-load contact in throttle switch. Additionally the EGR controller uses that signal.

15.5 Fuel pump

Jaguar cars typically have 2 tanks that can be selected via a switch from inside. That is also valid for XJ12 and XJ-S. The switch operates 2 solenoids. Fuel is pumped via an original Bosch fuel pump 0 580 464 011 or 0 580 464 012 (with non-retunr valve) with a rather high delivery rate of minimum 1050 cm³ in 30 sec and the Citroen / Volkswagen / Volvo connector. In the 80s Bosch recommended to use the Bosch 0 580 464 007 with 750 cm³ / 30 sec. That would be identical with the Mercedes-Benz fuel pump 0 580 464 005 except the connector. Today Bosch recommends the 0 580 464 999. I do not recommend that one as it creates high pressure pulses. Either use one of the ealier mentioned ones or the 0 580 464 013 for BMW L-Jetronic and 3 Bar system pressure.

15.6 Fuel lines and fuel pressure regulator

Jaguar has 2 intake manifold and 2 fuel lines, still they are interconnected. So each fuel line supplies fuel to 6 injectors and one cold start valve. So you will find 2 cold start valves and 2 pressure regulators in each engine. Pressure regulator is the standard Bosch 0 280 160 001, also labeled 0 280 160 013 with Lucas branding.Bei Digital-P Ist s wieder auf eine Ringleitung mit einem Druckregler zurückgeführt.

15.7 Cold start valve and thermo time switch

Both cold start valves C42161 (C44987 as of engine 85.5203 in XJ-S) are also Bosch built 0 280 170 033 or 0 280 170 035 with Lucas labeling. Their flow rate is 115 cm³ / min. Thermo time switch C42159/1 (USA/CAN 8s @i -20°C, up to  15°C, Bosch 0 280 130 213) resp. C44644 (Europe 8s @ -20°C, up to 38°C, Bosch 0 280 130 212). Late cars were equipped with (Bosch 0 280 130 224), injecting for 12 sec @ -20°C and opening till 35°C.

15.8 Temperature sensors air and engine

Temperature sensors air C42167 and cooling water C42166 are standard Bosch sensors. They are 0 280 130 006 (M8, 2x receptacles 2,8)  or 0 280 130 024 with Lucas branding and  0 280 130 014 (M10x1, 2 receptacles 2,8) or 0 280 130 025 with Lucas labeling for coolant temperature. You can use standard.

Now let us look at non Bosch parts:

15.9 Ignition distributor and trigger board

Ignition distributor, coild and pre resistors for coil are from Lucas. When D-Jetronic started so late in Jaguar Hartmann & Braun had already developed a breakerless ignition system based on indctive sensors. So this distributor has an encapsuled inductive sensor as Bosch also used it since mid of 70s. It would have been considered strange to continue to use a breaker system as trigger contacts. That's why this ignition distributor received an intersting change. Distributor housing got 4 threads and noses to carry a bridge for a PCB board just below distributor finger. This board was first equipped with 2 Reed relays, later with 2 Hall sensors. They were triggered by a magnet in the plastic housing of distributor finger. So each distributor revolution caused two impulses on both Reed relays or Hall sensors. The whole PCB board is a plug and play replacement for the trigger contacts of D-Jetronic. If you happen to still habe the Reed relay board, I'd recommend to swap it to AEU1683 as this board was known to be unreliable. The Hall sensor board needs additional +12V to work. So if you replace an older Reed relay board, you need to change the wiring. Voilà, an elecronic trigger contact. If I should find some time, I will also develop something like that for other D-Jetronic cars.

15.10 Fuel cooler

Jaguar does not use a damper but a real fuel cooler to avoid fuel steam bubbles. It is connected to air condition.

15.11 Inertia safety switch to interrupt fuel pump

As in all D-Jetronic cars fuel pump is controlled by ECU via main and fuel pump relay. However Jaguar has an additional safety feature. An inertia switch inside the car registers an accident and will disable fuel pump power supply. Great safety feature.

15.12 Auxiliary air valve (AAV)

Lucas build auxiliary air valve C42164 looks very similiar to Bosch AAVs. It seems to use the same expansion element. It has an additional bypass channel for idle-run adjustment screw. So you can adjust warm idle-run there. I would be interested to have a look at this AAV to see whether it has the same expansion element and holder as Bosch has. If yes, I would be able to repair it as well. So please, if you have a broken one, send it to me. I will disassemble and analyze it.

15.13 Exhaust Gas Recirculation (EGR) in USA/CAN/AUS

US and Canada always were more progressive in emission reduction. That is why cars for those markets have an EGR system installed. Such a system is also known from other D-Jetronic cars in the US. But Jaguar is the only one who has a controller for it. All others just rely on temperature and pressure sensors. The Lucas 2PR controller is connected to engine wiring harness. It receives information of idle-run and full-load from throttle switch and engine revs from output of ECU to amplifier as well as engine temperature via a dedicated switch. EGR is deactivated in idle-run and full-load as well as above 3500 rpm and it only works in a warm engine. It also receives information form an axle solenoid. I would be happy to learn what that information is used for. Basic idea of EGR is that exhaust emissions reduce oxygen in mixture, thus causing a slower and cleaner burning of fuel. You can deactivate this system without any harm to your engine, but of course that would increase your engine emissions.

15.14 Overrun valve in USA/CAN

Jaguar D-Jetronic ECUs did not use the overrun function block to switch off injectors. Only the very last ECU 0 280 001 025 for late California and Australia used this feature. When throttle valce is closed, all other ECUs continue to inject fuel according to engine revs. This causes a rich mixture and unburned fuel in emissions. While this is good for cooling pistons, it is bad for emissions and fuel consumption. Therefore Jaguar installed an overrun valve in the US and Canada that would let air flow into intake manifold in such conditions, making it possible to burn all fuel. I am unfortunately not aware whether this valve was omitted in late Californian and Australien cars with the 0 280 001 025 ECU. It would be unnecessary as this ECU switches off fule injection during an overrun situation.

15.15 Comparison to Lucas Digital-P (6CU)

Lucas called their D-Jetronic implementation system 3CU and further developed it to its own digital system Digital-P or 6CU for High Efficiency (HE) engines with higher compression and less consumption. It has a lot in common with D-Jetronic measuring principle. However componentes are very differen. Digital-P uses similiar injectors to D-Jetronic and also an amplifier. MAP sensor is integrated into digital ECU. Throttle switch is a positional potentiometer. Fuel pressure is increased to 2.5 Bar and in the USA a closed loop catalytic system can be connected. Similiar to Bendix's Electrojector ECU is full of low quality electronic components which caused many problems. Rumours say that there are no two ECUs showing same results on test stand. It was therefore soon replaced by Bosch L-Jetronic. If your run a Digital-P system, I recommend you ro replace it with L-Jetronic.


This article was done without support of Jaguar D-Jetronic specialist. I think that is a pity. While I was cordially welcome and promised all information when I approached the German Jaguar club a year ago, I later got no support at all. Whether that was due to lack of time or because he did not want me to publish information about the combination of Jaguar ECUs and MAP sensors, I cannot know. The only one who tried to support me within the range of his possibilities was Peter, the owner of Jag-forum-de. As there is very littls published about Jagaur D-Jetronic on and nothing by Lucas or Jaguar, it was very time consuming to find all this information. There is a small booklet from Jaguar (British Leyland) that preliminaily describes D-Jetronic. But it does not describe the differences between European and US cars nor EGR and it also has no spares list. But I now feel fit to completely diagnose Jaguar D-Jetronic components. However, I am still missing 3 Jaguar MAP sensor's reference measurements. If you are looking for a support in this forum, give me a chance to measure them before they are broken later.

Jaguar manual
Jaguar manual

If you need a manual, the only thing available is the blue booklet "Eletronic Fuel Injection - Provisional Repair Operation Manual" from Jaguar. Its information is limited and only in general. I found mine on eBay.

You will find spare parts lists for Jaguar XJ12 und XJ-S on I composed this information with my background knowledge on D-Jetronic, these spare part lists and the blue booklet.


I did also update chapter 11 Tester to describe both versions of Lucas Epitest D-Jetronic tester. First verison is well described in the blue booklet. At least it gives some information. In the meantime I also bought a Lucas manual describing version 2 of this tester including Digital-P servicing. If you need this or an Epitest tester you can contact me!


I hope to be able to shoot some pictures of Andreas's XJ12 during my workshop in June 2016. I will add them here afterwards.

This articel has created a longing for a Jag insides myself. I would love to ride an XJ-S convertible or even better an E-Type series 3 12 cylinder and convert it to D-Jetronic. Any good offers out there? Please let me know.

Your Dr-DJet (Volker)

Copyright © 2016 of this article and its content by Dr-DJet. Please post questions in forums and not via email or PM. I exclude all liabilities except those not excludable by law.