So I have a 1994 XJ12 x40 my vehicle will crank but not start. People were telling me it might be a crank shaft sensor. (The sensor that starts the fuel injectors,) not the fuel pump anyone that can help me with where is that? Pictures would be nice.

 

Don't know exactly where on the 12 but on the 6 its located at the front of the engine. You should see the reductor wheel (looks like a large gear cog with square teeth) mounted on the crankshaft at the lower pulley. The crank sensor will be mounted with the sensor almost touching the reductor wheel teeth. On the 6 it's mounted on the engine bracket at the top of the wheel, look for a thing with an electrical pigtail.

This might help too

https://parts.jaguarlandroverclassic...j6-xj12-parts/

 

The crank sensor is at the bottom of the crank pulley. Not the easiest to access. But before you do that you could check for spark by pulling a connected plug (with the corresponding fuel injector disconnected) grounding it and cranking. Or with a spark testing device. Of course you need a good strong battery to give you a fighting chance of cranking enough to discover the problem.

The last-gen XJS 6.0 V12 has nearly the same setup as your XJ81 XJ12 so you might start browsing there for ideas too. The name MARELLI comes up a lot regarding the attention needed for the ignition system with that 12 pot distributor cap.

Your car is even more rare than the XJS 6.0 V12, and so would be worth saving if its not too far gone.

 

He is experiencing a large starter sag during cranking at the instrument cluster

Reports below 9 volts

Probably does not have enough voltage left to properly run the engine ECU for regulation ( spark and fuel injectors )

Not confirmed but he probably has the MARELLI ECU system

 

My laptop is not charging up so may be out through the day resolving it

 

Additional information other then your starter sag observation

94 XJ12 Pump Relays.pdf (jagrepair.com)

 

So do I need to buy a new starter?

 

Lets do some troubleshooting before purchasing one

If you were at the point of removing the starter you can take it to a alternator / starter shop to be checked out

I think you have the 6.0 liter displacement V - 12 and would follow the wiring of the X40 chassis but would mechaniclly be the same hardware as the X300 6.0 liter block with the M ECU and not the last Denso ECU

The starter removal tips would be in the X300 / X305 section with some tips from folks in that section that have done

 

I’m available to do work on it right now what do you want me to check for you or do you need pictures of anything?

 

Need to verify you have the 6.0 liter block , for starter hardware

Pic of the ignition module component which is the difference between the M ECU and last Denso ECU version for the last couple of years

So you're a in between version as they were improving the V - 12

 

A quick check of starter part # that may not be accurate

Genuine Starter Motor For Jaguar Xj6 & Xj12 1987 - 1994 Classic | Jaguar Land Rover Classic Parts

DBC6924E and DBC6924N

 

Maybe this if it gets to it

Démarreur d'occasion de Jaguar XJS (1987-1996) Référence DBC6924 (jagpieces.com)

 

I’m headed to work right now but I wanted to send you a picture of this relay. I’m pretty sure it’s blown. This one was behind the battery on the right hand side.

 

I'm assuming you can put a 9 volt battery on it and make it click on the control pins

That is not a relay on the X300 model to source from

the pin twisted 90 degree out from the ohers should be one of the power pass through pins and the other will be across from it




Once you determine the pin map to know the power pass through sockets on the car side ...............................

Is it the 2nd fuel pump that may not be active in the starting sequence ?

 

It was it the car when I first got it (it does not click) so I replaced it with a similar one but this one has like a computer chips inside of it

 

It is a fuel pump relay

 

The one with a component inside it may be the second pump " module " and not so much a straight relay

This would be different then one with a diode in it for current polarity or time delay.

The module I think has to determine the RPM to close

 

You can jumper the # 1 fuel pump relay socket from 30 to 87

This may drain your battery with your keys in your pocket

You have 2 pumps to play with to get through the starting sequence

 

In the starting sequence the # 1 fuel pump may , and that's not sure , run for a very short time only and trap fuel pressure in the lines with check valves in each pump and the fuel pressure regulator

This would only accure with the # 1 fuel pump

On the later X300 models this fuel pressure will remain trapped for days

After storage to reset this trapped pressure rotate the key 5 times

any of the 2 fuel pump check valves can leack losing the trapped fuel pressure

Some have from reading placed a external to the tank of a certain size check valve

You can pull and leak check the fuel pressure regulator

A stuck injector can bleed off the trapped pressure

 

This is probably the 7th or so thread about the non starting issue with this car. Somehow, each attempt at solving this gets off track at some point. First recommendation from my perspective thus is to stay focused.

This particular thread was about the CPS at the beginning. Now we are looking at fuel pump relays (2 relays on the V12 in 2 separate locations). We also have the low battery voltage issue (9V) from another thread.

There's two things I would look at right now:
(1) 9V is too low for anything on any car. So, recharge a known good battery until full. Someting around 13 Volts, please. Put in in the car.
(2) Crank the engine, look at the tachometer aka rev counter and see if the needle moves. If not, the CPS is likely broken. (or wiring)

Once (1) and (2) above are confirmed, we could proceed further. Randomly swapping out electrical parts on XJ40 and especially XJ81 (V12) will be leading to confusion and nowhere.