hi all, I have acquired an 89 v12 with marelli ignition all of which is new to me and some help would be appreciated. the car just about starts and runs for a short time then cuts out. it runs very roughly. as a consequence we have stripped it down and changed all the plugs. I am going to fit a new distributor cap and rotor arm and new leads. somebody previously looks to have started the process and has made a mess of a lot of things. when we took the distributor cap off which was loose the distributor itself was not fixed tight. the three alan cap screws that hold it down were loose. can anyone tell me if this affects the timing and how I move forward. can it just be tightened down centrally or does it need setting ? also are motor factor parts ok ie rotor arm and cap? many thanks for any help

 

The timing is controlled electronically.

Get yourself a good workshop manual. Google "Jaguar XJS ROM" (Repair Operations Manual)

Google "Kirby Palm XJS experience in a book" Download that. Its free. Read the section about Marelli fires. Then read it again. Then read it again.

As with any car thats running but misfiring, you need to be careful you dont get the cats too hot during your troubleshooting as filling them with lots of unburnt fuel (because the fuel isnt getting burned in the cylinder) is not a good idea.

At that age, you need to replace all the short fuel injection hoses IMMEDIATELY, unless you are 100% sure they have been changed in the last year.

You will also need to look at the fuel injection harness which is down in the bottom of the Vee, and if it hasnt bee replaced yet, will be cooked and need rebuilding. Lots of info on this site about that, either DIY or one member is offering to make new ones for a fee.

In the end, to get 12 cylinders firing, they "only" need fuel and spark, so start with that first

History on the car? When was the last time it was running properly? Why was the previous owner messing with it?

For parts, where are you in the world ? (It helps if you add that info to your profile) There was a lot of myths about "genuine" Marelli distributor caps, but at the end of the day, if you read Kirbys book and do the mod he suggests, I think any cap will be fine. My car has a cap from somewhere like RockAuto here in the US and its been fine.

 

I bought a non running 89 Marelli car off of eBay. Many many hours of tracking down, rewiring the mess, only to finally conclude that the rear sensor was at fault. The rear "sensor" feeds the Marelli ECU a speed signal. If this signal doesn't match the VE tables set in the ECU, it won't stay running. It appears really complicated at first, but it really does follow the old adage "garbage in, garbage out". The "sensors" front, rear, as well as the ABS "sensors" are actually small electromagnetic pulse generators. They send a AC voltage signal to the ECUs, and in turn, the ECUs (Marelli and ABS), use this signal to compute engine timing, injector pulse duration.
Another problem I found was the distance of the crank "sensors" to their respective trigger mechanisms. (flywheel and trigger fingers on damper). Jaguar recommends no more than .045" from the flywheel. Mine was .047. I filed the mounting bosses and got them as close as I could shooting for spacing of .020".
If your cars runs at all, count yourself lucky. I don't really know of a way to accurately test the "sensors". In experience, I have found that testing them with a ohm meter won't work. A oscilloscope will from what I read, ut after buying a handheld unit, I felt I wasted my money because I still have no idea of what I was looking at.
The one thing I know for certain is that magnets degrade with heat over time and use. These are electromagnets. They fail on ALL cars that have them. It seems that Jaguar had a bad reputation to start with, so most throw in the towel when it really is the same kinds of parts that fail over time.

 

If you have more questions, feel free to send me your number in a PM.

 

As mentioned the timing is adjusted electronically but, as a baseline, the tip of the rotor still needs to be aligned with the appropriate post on the distributor cap.

My memory is foggy but I *think* there are some markings somewhere on the distributor body to do this.

Others will chime in

Cheers
DD

 

As mentioned previously, Marelli equipped models have an ignition system controlled by a digital microprocessor based system that receives input signals from a variety of analogue sensors:

MAPS (manifold absolute pressure sensor) is located inside the Marelli Powertrain Control Module Ignition (PCMI) and connected to the rear of A bank inlet manifold by an air pipe, this measures engine load.
IATSI (intake air temperature sensor ignition) is located in A bank inlet adjacent to throttle body, it is a negative temperature coefficient (NTC) thermistor whose resistance varies with temperature (resistance decreases with increasing temperature)
This is used to retard ignition timing at high inlet temperature.
CKPS (crankshaft position sensor) is a variable reluctance sensor, three toothed wheel attached to crank pulley passes by this sensor (coil wire wrapped around magnet, magnetic field disturbed by close moving teeth induces voltage signal in coil as teeth pass. This gives 8° ATDC reference for each cylinder on A bank, with B bank being derived by PCMI.
Sensor gap is 0.2 to 0.8mm (6 litre)
Or 0.018in to 0.042in (5.3 litre)
CKFS crankshaft flywheel sensor is variable reluctance device produces engine speed reference by ring gear teeth (160 teeth situated near starter ring gear, same air gap.

After further reading of repair operation manual it seems I didn't emphasise differences between 5.3 and 6.0 with reference to Marelli ignition:

Both have primary inputs to Marelli system that are tdc sensor (ckps) and flywheel or crank speed sensor (ckfs)
There are secondary control inputs to Marelli ignition system that do not prevent the engine from starting if faulty but do influence ignition timing. These secondary inputs are different in 5.3 and 6.0

In 5.3 they are coolant temperature sensor in A bank water rail, an NTC thermistor, this is a variable resistor whose resistance decreases as temperature increases. Its purpose being to vary or trim ignition timing as engine warms up. Also an air temperature switch is fitted to rear of A bank air cleaner on 5.3 to retard ignition timing if inlet air temperature is 75℃ or above.
Secondary inputs to control ignition on 6.0 are intake air temperature sensor ignition (IATSI) an NTC thermistor located in A bank air inlet near the throttle body to retard ignition timing above 25℃ inlet temperature.

Both 5.3 and 6.0 use throttle idle switch.
Both have ignition map select link for 95 octane fuel (link in) or 91 octane. Both have temporary retard at request of auto gearbox (to reduce torque for smoother gear change)






Inside Marelli ignition control unit

 

think I need to get some help

 

brinny , where about are you in the world ?

you may also need to check that the fuel pump is making the required 4bar of pressure , as the car can start but then starved of fuel , this is a common problem , and is usually caused by a blocked pickup filter in the swirl pot under the boot/trunk battery

this is an easy fix if it is the issue, and is zero cost, so prove your fuel first, then prove the integrity of the injector wiring looms , the injectors are controlled in four banks of three at a time, the power module behind the right front headlight can be corroded on the contacts causing very poor running

i would then check the coolant sensor , as this would stop the car running, as does the air intake sensor on the left air plenum box, if either of these are loose or disconnected the engine will fail to run

i would also ensure the vacuum pipe from the engine to the boot/trunk mounted ECU by the battery is intact and connected to the ECU , this gives engine load reading for the fuelling

its a process of elimination , prove one item at a time and then move on

i would also personally ensure you use a genuine Marelli cap and rotor arm ( with or without the modification ) as the lesser aluminium caps have been more prone to burn out, the brass contact Marelli one doesn't ,

it can all seem complicated, but bear with it

then its onto the two sensors on the engine , one on the front crank pulley and the other mounted by the gearbox onto the flex plate flywheel position , as mentioned, as close as possible without touching the wheels, usually between 2 and 4 thou as suggested above


good luck



BB

 

thanks bb that is a good way to go about things and helpful. im not very up on the technical names of things but looking from the drivers seat the air filter box on the right has a round object going to it that is loose? I live near Sheffield south yorkshire

 

that round object is the ' extra air valve ' for the aircon ( i think ) to stop it stalling out under load at tickover , it should be air sealed into the box, but not necessarily ' tight fixed '

your a bit too far for me to pop in as I'm down in Glos,

but keep at it,

air and water sensors can be seen here, ( i have different intakes but the wiring is the same ) , the air is onto the top of the ally intake as seen , trace the wiring back six inches and a branch off for the water sensor is there as well, ( if not gone they are usually marked ' air' and ' water ' , either of these are off means she won't run


IMG_0053 by MyPix on Talk Photography


the ' flywheel ' pickup sensor can be seen in this picture, its right behind the oil filter by the far exhaust on the flywheel cover plate

900 by MyPix on Talk Photography

BB

 

many thanks bb. I now have a list of things to check/ replace and will report back. could you tell me or post a photo of how theextra air valve is held in the airbox please . much obliged to all who have assisted so far

 

its simply held in by the rubber sealing ring/grommet , the pipe that exits this electrical air valve goes to under the right hand throttle body ,

good luck with the investigations

BB

 

one last thing can you help with any suppliers or part numbers for the following. the top dead center sensor, the engine speed sensor and the coolant sensor. I think this is part number dbc3728 if ive got the right one . many thanks

 

From what I now see, they are the same part number on the 89 Marelli car..DBC12507

In the UK..Part no. DBC12507 | Crankshaft position sensor parts from Jaguar Heritage Parts UK

 

Gearbox related timing retard on V12 did not come until 4L80E /6litre combo. Was not present on 5.3.

 

we have today changed the rotor arm the distributor cap and the leads. fired right up and ran for a minute or so lovely then spluttered and died which it has done before. 4 gallons of fresh fuel in the tank. will not restart but leave it for a day and it will do the same. run stop not restart. any suggestions gratefully receieved

 

Sounds like you are losing the spark. Have you checked for spark when it will not restart? No spark under these circumstances sounds like amplifier giving up after a minute or two, but I have no marelli experience; just a thought.
It is either fuel or spark disappearing, so also, next time it stops, check fro fuel and injector clicking as well as for spark.
Have you replaced the position sensors as mentioned earlier by other posters?
Greg

 

No I haven't done the sensors yet. Would that cause it?