Ok this one is really bazar. A week ago my car wouldnt start. It clicked and when I reset the key it started.
Then a few days later it did the same thing.
Then 3 days ago my 1998 XJ8L wouldn’t start at all.
I called my shop that works on it and they summoned a tow truck.
All I would get is a click in the area of the glove box.
My mechanic pulled the starter and tried to motorize it on the bench. It wouldn't turn over so we put in a rebuilt starter.
I picked up the car later that day and drove it around with no issues.
The next day I had to run some errands.
I made three quick stops and then went to the grocery store. Up till now the car started every time.
I spent one hour in the store came out and it would only click.
Had to have a tow to the shop again. The shop was closed so it sat over night.
The next morning the mechanic, and I thinking it was a relay, was going to work on it and it started right up.
He spent 4 hours trying to make it malfunction so he could diagnose the problem.
We even moved the relays around thinking if it was a relay we would put the relay in the air conditioning place and move that one to the starter place. 4 to 5 attempts in 4 hours and every time it starts.
Even when I picked it up it fired right up.
So I pick it up at 12:30 and drive home. 2 hours later I go out and it will only click.
Called the mechanic and we decide to reset the computer by disconnecting the positive lead.
After 10 minutes I connected the lead and the car starts. I even shut it off and it fired right up. Here is where the bazaar part comes in.
I let the car set for about a half an hour and I try to start it and it just clicks again.
So once again I disconnect the positive lead and let it set for 10 minutes like before and now it will not start. Just clicks.
I have jiggled the shift lever in hopes it might be the neutral safety switch but that doesn't do anything. Any Ideas?

 

There are some bulkhead connections in the positive circuit, and also several ground connections which should be cleaned. Don't miss the one from the power bus fuses in the boot. It does sound like a connection problem to me.

 

To add to the frustration after attempting all of the above I went to my grandsons Bday party last night. The car sat for 6 hours. When I came home it started right up. I shut it off and started it in neutral. Wouldn't that dispelled the neutral safety switch? As for ground connections we have checked all those already. Could this have anything to do with the body control? I understand it controls the anti theft mechanism. If so where is it located?

 

I've put some line breaks in your first post to make it easier to read.
I know you say you've checked the earth points but this sounds like a straight battery connection problem.
There's an earth strap from engine to chassis that can cause problems also the crimp to the positive lead cable at the battery.

When you say 'click' it isn't the relay on the starter clicking?

ps Also worth putting your car details in your signature
User CP (top left)>edit signature

 

Thank you for the grounding info but we have checked all those leads. The car is getting power to all circuits and the battery is fully charged. Everything works except this chronic problem. My mechanic had a late model corvette jn recently with similar symptoms and it turned out to be the body control. That's why I asked where it is located on this model Jag

 

Also the clicking sound is coming from the area behind the glove box
I can only do so much as Im alone
When I open the door and try to hear the engine compartment then bells for the door being open influences the sounds.
There is some sound coming from the intake manifold but I suspect those are normal
The click is just that a click.
Its like a relay engaging but under the glove box. But keep in mind im setting in the drivers side to hear this

 

Try setting a mobile phone to record video and putting it as near the starter as possible - then maybe move it about a bit to see if you can get a fix on the sound.
This isn't my model but certainly if the main starter relay clicks it isn't the BPM.
I strongly advise downloading JTIS from the HOW-TOs here - it will answer all your location + wiring queries and much more.

 

Do a search on my intermittent no start -fixed- faq. I had a similar problem that I fought for about a year. two independent jag mechanics and a jag dealer could not figure it out until a mechanic had the same vehicle as mine and they started part swapping. problem was key exciter coil or key transponder. Worth a little bit of reading. Mine would always start in the morning ,but running around town it would finally give out and not start.

 

The only way to find electrical faults like this is to get the actual circuit diagram & learn how it operates-then use 2 or 3 multimeters at various strategic points to monitor what happens when you try & start the car.

You need to find out where the 'cranking' signal is disappearing, as the starter relay is energised by the Body Processor Module (BPM), which itself receives 'crank engine' & 'security acknowledge/ok to start' signals from the ignition switch & the Key Transponder Module.

Your first point of measurement should be to monitor the BPM output drive signal to the starter relay. One side of the starter relay coil is fed by an ignition-controlled +12V rail, and the BPM 'earths' the other side of the relay coil to energiuse it & apply power to the main starter solenoid on the starter motor itself.

So the first place to connect a multimeter to is the actual coil of the starter relay. You will need to 'piggy-back' a couple of very thin wires into the spade receptacles after removing the starter relay for access. Then connect the multimeter to the 2 piggy-back wires.

Turn the key to the 'cranking' position & see if you measure any voltage at the starter relay coil-it should be around 10v or so during engine cranking, depending on battery condition & ambient temperature.

If you get the correct relay coil voltage, then the fault will be somewhere in the main high-current power feed to the starter motor, so you will then have to do some more monitoring further along the circuit route.

If you don't get any relay energisation voltage, then the BPM is not giving the correct relay drive signal & you then need to monitor the inputs to the BPM. The obvious first line to check is the 'crank' signal from the ignition switch itself-this is the primary command line to crank the engine. If this signal is not present, then there is a fault in the ignition switch or key.

The next line to check is the 'neutral' switch, to see if this signal changes whenever you have the gear selector in the 'N' or 'P' position.

If that's ok, then you're looking at a fault with the BPM or the Key Transponder Module.

But to do all this you will need the circuit diagrams-without these you cannot do anything meaningful. A lot of the signal lines work by earthing a module input line from the ignition switch or neutral switch etc, so normally the input line would be 'floating' at a higher voltage & is then earthed when the relevant switch is engaged.

Don't rule out the obvious stuff either, like a faulty battery. The false bulkhead connector at the front is absolutely critical to the starting & charging circuit. It supplies the main high current line to the starter & also the charging current from the alternator output back to the battery.

If this connector goes intermittent then you will get intermittent starting. Also, the charging will become intermittent & the battery may lose enough charge to cause starting faults as it doesn't have enough cranking power in it.

Another thing is to make 100% certain that the rebuilt starter fitted is still working ok...

 

Absolutely great advice. Thanks to the last two posters. One other thing can you tell me where the BPM is located? This seems to put logic to the problem that may lead to a solution. Thank you so much

 

As I said, download JTIS. It's all in there.

 

One more question: Steve said if the relay clicks it isnt the BPM. I tried his suggestion and put a phone next to the realy and it does click when the car wont start. Are you still thinking it could be the BPM or the sending ring?

 

Steve where do I find this? I looked above at all the tabs and I dont see where this is.

 

Try downloading the PDF in this link, in my opinion easier than the installed JTIS

https://www.jaguarforums.com/forum/x...at-x308-81022/

 

And for parts, either use JEPC or Genuine Jaguar Parts and Jaguar Accessories for Classic Jaguars from Jaguar Classic Parts UK
They have all the part numbers and exploded views.
Its handy if you have a smart phone at your car's location to check something quickly.

 

I know you said you checked all the connections, but when it won't start and just clicks, grab hold of the ground strap and see if it's hot (don't really grab it !). If it is, you have a bad connection. This happened to me and I replaced the ground strap with conventional cable (also ground under car near tranny). The braided cables can lose good connection at the crimps.

 

I have the same exact problem but I can usually get mine to start after a few tries. When I turn the key its not even engaging the starter. I had this problem before with another car and it was the security chip in the key. The car would not see the chip and would not even attempt to crank the motor. I replaced the key and the problem went away.

I have one key for my 99 XJ8 that will not start the car many times. I have to remove the key, flip it 180* and try it again. Most of the time this will get the engine going. I have since banished that key to my backup keys ring in my bedroom closet. If you have a second key try it for a few days and see if the problem goes away.

 

Red October,

I like your plan for tracking down the no start condition (as I have a similar issue).

Question 1:
Your first point of measurement should be to monitor the BPM output drive signal to the starter relay. One side of the starter relay coil is fed by an ignition-controlled +12V rail, and the BPM 'earths' the other side of the relay coil to energiuse it & apply power to the main starter solenoid on the starter motor itself
--> If I take out the relay and insert a 12v beeper, that I have, it should beep. Problem of working on your own and not having 10ft long arms (cranking and measuring).

Question 2:
According to the pin out information the "OK to start" from Key Transponder and Engine Control Modules are "encoded communications".
Any idea what to look for on that line? Do you need a scope to look or is any change in signal evidence that its working?

Thanks

Lincoln

 

Fishfoolbear,

1) Yes, if you take the relay out & connect the beeper to the connections that feed the relay coil, then it should beep when you turn the key to the cranking position.

2) I don't know what the encoded communications signals should look like-you could connect a scope & then see if anything changes on the signal lines when you put the key in the ignition switch.

Normally, if you don't know what kind if signal you're looking for, then you just see what signal is present there & if it changes when you put the key in the ignition. You're looking for something to change when you put the key in the ignition.

If the BPM is suspect, then you'd have to substitute a known good unit. If the starter relay is not being energised but the crank signal is present from the ignition switch when you turn the key, then it only leaves the BPM or the key transponder module-or the key itself & the ignition switch sensing pickup that detects the presence of the key in the ignition switch.

 

If the starter relay clicks/gets 12 V when you turn the key the problem lies either in the starter motor or its connections. There's nothing wrong with the BPM or security stuff.

Check starter earth by connecting one side of your voltmeter to the starter body and the other to a known good earth.
If you get a voltage of more than 1V or so when you try to start it is the earth strap to the engine.

If you're getting 12V on the big supply terminal to the starter and that drops to very little when you try to start the problem is in the cable from battery +ve to the starter
OR battery grounding.

To check battery grounding put one voltmeter lead on the lead battery -ve post and the other on a known ground. If you get a significant voltage trying to start the problem is battery ground.

Hope that makes sense.