Hey everyone,

I have a 1992 XJS V12. A previous owner obviously had some sort of starting issue and mounted a button starter under the dash. to start the car you turn the key on and then press that button. This is my first Jaguar but I assume most likely issue there is in the column ignition. My real concern is that this setup seems to only work about 80% of the time. The other 20% of the time you hear the starter but the engine doesn't turn over. When that occurs the car WILL start but only after getting a spray of starter fluid in the air intake. It doesn't matter if the car is hot or cold.

I assumed this was a fuel delivery or tune up issue and had the following work done that I knew I should do anyway: new cap and rotor, plugs and plug wires, fuel lines, fuel filter. The shop said the fuel pump was working well and I believe that since the car runs great once started. Also had a compression test done and all 12 cylinders are good.

Any thoughts on what could be causing this frequent no start? could it be related to the jury-rigged starter button? Much appreciated,

 

If you hear the starter, the button is sending 12 Volt power to it. If you hear the starter but the engine isn't 'turning over' the starter solenoid isn't engaging the starter with the ring gear. If you mean by 'turning over' the engine isn't firing then the issue is fuel, air or spark delivery.

I have a hidden button too but all works well.
Luck, RagJag

 

Have you checked the earth strap from the engine to the chassis?

 

Sorry I'm a novice, what is the earth strap and how would I check it?

 

Does the fact that it will start with starter fluid when it doesn't otherwise start indicate anything? That is why I assumed fuel issue to begin with, but if its not the pump, lines, or filter I don't know where to turn to there, or could that be spark?

 

TweeTwee, If it starts with starter fluid, does it continue to run or just cut off after the fluid burns off? If it runs with the fluid but quits, you have a fuel delivery problem.
I do not have any experience with V-12 engines. Mine is a 4.0 inline six. Maybe some V-12 owners will chime in. This problem is intermittent and as such, difficult to find.
RagJag

 

Once it starts it runs great and does not quit, even if it needed the starter fluid to start. Thanks again, I know its a bit of a moving target issue.

 

Twee
I have read this thread twice, and I still do not fully understand the exact symptoms. Could you answer these questions clearly, please?

1. The engine always turns over on the starter? yes or no?
2. The engine when it turns over on the starter sometimes fires but not always? Yes or no?
3. The engine when turned over on the starter, IF it sometimes fires on petrol, it will NOT continue to run, yes or no?
4. When the engine turns over on the starter but does NOT fire, squirting starter fluid into the intakes ALWAYS gets it to fire? yes or no?
5. When the engine is started on starter fluid it ALWAYS continues to run normally on petrol from the tank thereafter? yes or no?

Greg

 

Yes, two things going on.


1. The button starter is a substitute for the start position on the ignition switch. Turn the switch to run, then push the button? The button may be wired to send 12v directly to the solenoid on the starter, thusly bypassing wires and a relay. that can be fixed or just live with it.


2. Priming with starter fluid, (ether) and getting the engine to run indicates a fueling issue. Failure of a cold start feature???


Carl .

 

I apologize for being unclear.

1.) No. I always hear the starter, but sometimes nothing from the engine
2.) Yes, It will start ~80% of the time with nothing else needed
3.) No, if the engine fires it always runs and continues to run, I never have a start then quit situation
4.) Yes, any time it does not start from just the starter starter fluid will make it start. This has never not worked.
5.) Yes. It will always continue running once started.

 

Thanks Carl, where would you start with this? I know the fuel pump is good and the lines and filter are new.

 

Twee
Thanks for the clear replies. One more question about when the engine IS actually turning over on the starter. The 20% of the time it does NOT start, but the engine IS turning over, starting fluid then WILL get it to start? Yes or no?


In this reply I am assuming YES, if I am wrong ignore what follows! Therefore your main problem is unreliable fuel delivery on starting the car. As once the car starts, it always continues to do so, this indicates to me that it is initial fuelling that is the problem. As, the car will always start on fluid if it does not on petrol, providing the engine is turned by the starter motor, then this eliminates many ignition-related electrical causes. I respectfully disagree with JagCad and I do not think this is anything to do with cold start injectors, which your car may not even have. The V12 will start quite OK with no such items fitted to it, and so will yours on petrol or starter fluid.


Some ideas: The V12 starter motor relay (the electrical unit that activates the starter when you turn the key during the starting process) has to send a signal to the ECU in the boot to tell it to fire the injectors while the starter is turning the engine. If this signal has become a bit unreliable, or its wire or connections have, it could cause your problem.


I have a pre-facelift (earlier version of the car) and the starter relay is under a black plastic cover in the engine bay on the inside of the wing just forward of the RHS hood fixing near the firewall. Your later built car may be DIFFERENT, so if the unit is not there, post again and a later car owner will tell you where to look. You undo the cover and there is the relay. It is about 2 inches by 1.5 inch by 1 inch silver unit with five electrical connectors to the underneath. Remove the battery positive terminal (for safety) and CAREFULLY remove the relay from its fixing, and then one by one remove each connector and clean it and the post on the relay that it clips onto. If the relay seems old and beaten up, buy a new one as the problem could be internal to the relay, but it must be a genuine Jaguar V12 starter relay and will cost quite a bit (maybe 50 USD) at least they do over here.


The other end of the wire I am referring to ends up at the ECU in the boot. If your work on the relay makes no difference, post again and people can help with the next stage of testing on the wire to the ECU and the ECU plug.


Greg

 

I would bet they are unrelated issues, and the starting fluid isn't really needed. I chased a problem like this once. Had the starter rebuilt, put a new starter relay, yet still had intermittant starting issues. It wound up being the cable going from the post on the firewall to the starter. Just a bad starter wire. Sometimes good, sometimes not so good a connection. New cable resolved the issue.
If I suspect fuel issues, my first check now is the temp sensor on the left front. I check it first at the sensor for relevent resitance value with a digital volt meter, then I unplug the main connector from the ECU in the trunk, and check it there. If they are different, it is most likely the wires that run between the temp sensor, and the throttle pedistal. They literally get cooked to the point they either fail completely, or the resistance values change so much that the ECU simply can't signal the injectors properly. Once it starts however (with starting fluid), the temp sensor isn't quite as critical, yet still needed for proper fueling.

 

Update here. I took the XJS for a long (200 miles) drive for the first time ever and at the end, with the car at warm but not overheating operating temperature it began wanting to stall out when at idle. It would restart after stalling but I think this is definitely a fuel issue and might be related to the weird starting? If so should I begin with changing the fuel pump or the pressure regulators? Thanks so much everyone

 

Running at speed OK and not at tickover is not obviously a fuel starvation symptom.


Have you tried adjusting the AAV slow running screw, which might have got crudded up? Also the throttle butterflies might need adjusting, as this is more of that sort of symptom, if the car starts right up after stalling and (I presume) can be kept going on the throttle pedal?


What did you do to fix the starting/not starting problem?
Greg