Hi !
I got an XJ40 1990 4.0 AJ6 for a few weeks now.
All was working well, very nice car. A fex days ago, I find Andy's bracket, so I buy one, and as soon as I goot it, I mount it on my car : very easy work.

The car starts at first try, and I take it for a ride to 3Km, to a supermarket. When I bought all my stuff, I go back to my car, the motor starts immediately, I pull the car outside its parking spot and ... the motor stalled, and it never start again

My neighbour pull my xj40 with his pickup to my home.

I thought the CPS did not liked the manipulation. So I buy a new one, but still the same.

• I put back the original CPS bracket : still the same.
• When I turn the key, the needle in dahsboard show about 200 revolution per minute.
• I got about 1.4 kOhm on ECM plug for CPS sensor

I made some tests :

- spark from the coil :

- fuel pressure :

Now I don't know what to check
Any advice will be much appreciated, and I hope my english was easy enough to understand my problem.

Carmelo

 

Try fitting a new rotor in the distributor. Sounds like this could be the problem.

Larry

 

@Lawrence Thanks for advice. When you speak of rotor, do you mean JLM381 ?

 

yes

 

You could try the same thing you did with the cable directly fromt he coil with one of the spark plug leads.
If that works the rotor should be ok.
Could also be the cap.

But the small time between the change of the bracket and the error is really suspicious.

Did you accidently disconnect something else?

Did you check the fuses?

Maybe the cable of the sensor is damaged. You could try to wiggle at the cable while someone starts the car.

 

Hi Carmelo,

Welcome to the Jaguar Forums! It's great to have you with us.

I'm sorry to hear of your cranks-but-won't-start condition. The first thing I would suggest is that you check your Vehicle Condition Monitor for any stored Diagnostic Trouble Codes. To do so, turn the key to position II (ON) but do not crank the engine. Press and release the VCM button on the trip computer next to the steering wheel. Watch the display below the speedometer where the odometer / mileometer / mileage counter / tripometer is normally displayed. DTCs are displayed in that window as "Fuel Fault" or "FF" plus a two-digit number, such as "Fuel Fault 24" or "FF89." Write down any code exactly as it appears and post it here and we'll try to help.

The second thing I would suggest is to check all of your wiring and electrical connectors that could have been disturbed while you were changing the CPS bracket. Also check your fuses in all three fuse boxes.

An English acronym for an engine's requirements for starting and running is FAST: Fuel, Air, Spark and Timing.

Your fuel pressure is low - I think it should be at least 40 psi. But you do have pressure, so we assume your fuel pump is working. To test for a plausible power signal at the fuel injectors requires a noid light or oscilloscope, but you may be able to measure a small alternating current (AC) voltage between the two terminals at each of the fuel injector electrical connectors.

It would be worth checking your air intake plumbing for any leaks that could lead to excessively lean running. Especially check that your Mass Air Flow sensor (MAF) is connected properly with no air leaks in the pipes between the MAF and Throttle Body (TB).

Since your tachometer reads about 200 rpm while cranking and you have spark, we assume your crankshaft position sensor (CPS), ignition coil and ignition amplifier are working.

As far as timing goes, the only thing I can think of that could lead to your problem is if your distributor clamp was loose and the distributor rotated out of time, perhaps due to being bumped while you were changing the CPS bracket. It's easy to check by grasping the distributor and attempting to rotate it clockwise or counterclockwise.

A very helpful reference is the Haynes repair manual. You can download a mostly-complete version at the link below:

Haynes Jaguar XJ40 Repair Manual

Another very helpful reference is the Engine Management manual, which you can download at this link:

Jaguar AJ6 4.0L Engine Management System / OBDI Diagnostic Guide

And the wiring diagrams are available at this link:

Jaguar XJ40 Electrical Guide 1990

Please keep us informed.

Cheers,

Don

 

Hi !
Thanks a lot @Lawrence @Don B @Browny2

I might find the problem tonight : the rotor cap.

I have the Jaguar AJ6 4.0L Engine Management System / OBDI Diagnostic Guide and check the ignition like that :

- Between coil out and ground : lots of spark when I crank
- between coil out and "rotor finger" (JLM381 part) : lots of spark, as you can see in this video I made :


And look what I found :




I think my rotor cap is shot ! (It was changed by the previous owner 3000Km ago ...

What do you think ?
Rotor finger + rotor cap ? (I don't know the exact words in english)

 

The rotor has a resistor potted in that red part. It fails and spark does not travel to cap

larry

 

I just measured the resistor between center and extremity of the rotor : 0.9 kOhhm.

 

Hi Don,

First thing : I checked the VCM : no fault stored.

Second thing : I checked the wiring this way : In AJ6 diag manual, we are told to measure on ECM yellow plug between 13 and 24 pins : I got 1.4 kOhm, so I assume the wiring from CPS through ECM is good.

I look at the inscription on the 3 fuses boxes covers : it seems there is no fuel / motor related fuse ? Am I wrong ?

 

Hi all, sorry I don't want to sound dense or sidetrack the thread but if Carmelo has an XJ40 with a distribution, why does he need Andys bracket? I'm assuming you could get the 5 deg advance adjustment needed by rotating the distributor.

 

No, on theses motors, the rotor adjustement doesn't impact the timing. (It is what I have understood !)

 

The power for the fuel pump is delivered to the fuel pump relay from a direct connection to B+ battery power, so you are correct, no fuse in the fuel pump motor power circuit. Since you have 30 psi of fuel pressure we assume your pump is working at least somewhat, and we also assume there is sufficient fuel in the tank. When you turn the key to position II (ON) without cranking the engine, you should be able to hear the fuel pump run for a few seconds to prime the fuel rail.

 

Exact ! I hear the pump running for a few seconds when I turn the key.
I have ordered distribution cap, rotor and pressure regulator. They should arrive on Tuesday ...

 

The ECM controls timing based on engine load and speed according to a matrix of strategies stored in memory, so timing is somewhat independent of distributor rotation. However, if the distributor were rotated to a sufficient degree to change the mechanical firing order, the ECM could no longer fire the correct plugs at the correct time. You can see from the distributor diagram below that if the distributor were rotated more than 15 degrees in either direction, the rotor would fire the incorrect plug:




Cheers,

Don

 

And, the winner is ........... @Lawrence

Look at his picture I extracted from a video I made yesterday :



So ... the rotor is shot as it is grounded !

I tried something : I put lot of grease between the rotor and his axle and ... the car started right away
Now I'm waiting tuesday to receive the new rotor and new cap.

Thanks a lot everybody for your help

 

Hi !

I received my replacement pieces this morning :
- fuel pressure regulator
- distributor cap
- distributor rotor

I don't have anymore the loss of pressure as I cut off the pump.

The car started right away, I did take it for a little ride, it runs well until 3000 rev/minute : I can't go upper !!
:'(

Any idea ?

 

Hi Carmelo,

When the engine speed is limited to 3,000 rpm, the car may be in "Limp Home Mode" or "Limp Mode," (LHM or LM) due to a fault somewhere. Sometimes LM will be accompanied by a warning light on the instrument cluster that looks like the outline of a transmission/gearbox.

Start your diagnosis by checking your Vehicle Condition Monitor again for any stored Diagnostic Trouble Codes, as I described in post #6.

Then double check all of your work to be certain all electrical connectors are clean and properly fastened. In particular, check the electrical connector for the Throttle Position Sensor (TPS).

Cheers,

Don

 

Hi Don !

thanks for your answer.
I think I'm just out of luck : I have bought 2 new CPS sensor : one of them was bad. I put the other, and now the car is running fine ...
I did not had the check engine light when I was in Limp Home mode, and I did not watched if there was error in VCM at the moment

 

Hey

It's me, again

Look at that :


I think there is Ghost inside my XJ40 ...