Engine cranks good but makes no attempt to start. I welcome all suggestions

Hi Jag lovers. I have an issue with my 1994 xj40. It was running g great until this morning when it would not start. It would crank forever but did not make any attempt to start. Not the slightest indication of wanting to fire. Checked fuel pump fuses, swapped the fule pump relay to no avail… Have spark at the plugs, sprayed starting fluid into the throttle body, nothing. Am turning my attention to the crankshaft sensor. Would the sensor go bad and throw off the ignition timing so plugs still fire but car not run? Any comments would be greatly appreciated. Thanks

Hi Gary and welcome to the forum. If you are seriously interested in learning more about the magnificent motor car that is your XJ40 - and if you have a significant amount of time on your hands - check.out this thread, which may hold the record as the longest XJ40 thread ever: 1994 Jaguar VDP No Spark?
If you would rather just cut to the chase try replacing / swapping the IgnitionOn relay.

Gary, by any chance did you start the engine and only run it for a short time and then stop the engine? Its possible you have bore wash. As you say you have spark and fuel then the engine should run. Does it sound as if the engine is turning over quicker than normal? If it does then take the spark plugs out and drop a teaspoon of oil into each bore and then replace and try to fire the engine.

Hi Robin and thanks for your replly.
No, I did not start the car and turn it right off again. I had driven it about 20 minutes, pulled into the garage and shut it off. The next morning I went to start it and that’s when it failed to fire. I should add that typically it would start right up 70% of the time, the other 30% it would crank and not start until I turned the key then immediately back on and it would immediately start. No problem. I had been passing off the issue assuming it had to prime the fuel injectors before starting. I seem to remember having that same issue 5 years ago until it finally wouldn’t start. I replaced the crankshaft sensor at that time and the problem went away until now. That’s why I was considering the crank sensor to be the offending unit.
One other point, I replaced water pump a week before this current problem started. When I ran the engine to check for leaks etc. I had a loud rapid puffing air/vacuum sound and realized a vacuum hose had become unattached. I took the drive belt off the air pump so I could finish the leak test. I drove it like that for 3 or 4 days before my non-start issue. Sorry this was so lengthy but something which seems unrelated to me might help someone else identify the problem.

The crankshaft sensors are prone to failure over time; so, if replacing it worked 5 years ago, try it again.

What you explain here is a classic symptom of loosing fuel pressure in the fuel rail during a shut off period. Cycling the key to on and off causes the fuel pump to run for a few seconds bringing the fuel rail up to pressure. I would fit a fuel pressure gauge to the rail and see what the pressure is. As I recall it should be 35-40 lbs.

Thanks John for your reply. I will see what I can do about a pressure gague as you suggest. I personally don’t have such a thing but I may be able to beg, borrow or steal one somewhere. If nothing else it might indicate the general health if my fuel injection system.

Thanks JGL for your reply. I went ahead and ordered a sensor on line if, for no other reason, the local parts stores no longer have a source for them. Better to have it and not need than need it and can’t get it.

Hi Mike, I do have spark at the plugs so I don’t know if the IgnitionOn relay would be my problem but it is something I will look into it. I’ve had this car long enough to know you can’t take anything for granted and the obvious is often overlooked.

Gary I sent you a personal message.

Quick way to diagnose the crank shaft position sensor…crank the car and watch the tach. If it just sits there at the bottom of the dial, not moving, replace the cps. If it jumps up to around cranking speed, like 400-600 rpms, it’s probably not the sensor. My car ran perfectly and one day would not fire at all. I read about this and watched the tach—no movement. Replaced the sensor, back to running perfectly. I got one on like for around $65 USD. I later ordered a second that I carry in the car as a spare as I still take long road trips in my 26 year old X300.

Hello Frederick, Thanks for your suggestion. I went and tried that and found that the tac needle wobbles between 0 & 100 RPM. I already ordered a crank sensor.
One more clue to cloud the issue, I turner the key on and hit the VCM button to zee the error code and the code display screen was totally blank. No code of any kind d displayed.

Hi Robin, You said you sent me a personal message but I don’t know how or where to receive it. Was it email, text message or somthing on the Jaguar Forum?

Little blue circle top right of this page attached to your avatar.

Before you go one step further replace the distributor cap and rotor … roll your eyes at your own expense.

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Spark yes, but if it’s not blue and big you probably need what Groove mentioned above!

Replace the leads also.

Thanks again. I pulled the cap and rotor and they are burnt. I cleaned them up but still no start. My local parts store has the rotor but has to order the cap. I have to go elsewhere for the condenser and ignition amplifier.
I take all comments seriously and appreciate everyone’s efforts to help me.

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Replace the rotor right away. The Jaguar XJ40 rotor has a resistor inside it that prevents radio interference. These resistors go high resistance and open circuit.
I was towed 20 miles once because I didn’t have a spare. Put the new one in when I got back to base and she fired right up. Cheapest fix you’ll ever do.

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Fast and cheap, that’s what I like. I will do that today. I cleaned the contacts on the cap and rotor yesterday to no avail. Thanks for that suggestion.