Strange no-start behavior

I’m posting this here because my ’94 XJS has the same AJ6 engine as the XJ-40

BTW, this is not a battery or a starter problem, as the engine does cranks beautiful. This afternoon I was taking my 1994 XJS, 4.0L straight six to the smog check shop. After driving about three blocks I realized that I forgot to bring along the registration paperwork. I made a U turn and drove back home. I parked the car on the driveway and left it running for about a couple of minutes to go get the paperwork. Up to this point there was absolutely nothing wrong or strange with the way the engine runs. After two minutes I came out of the front door and realized that the engine had stopped running, although the ignition was still ON. Turned the ignition OFF and then I tried to start the engine again. Well, it did crank but it wouldn’t start. I tried it many times, but it just wouldn’t start. I tried to start it again some three hours later with a cooler engine, but the car just simply will not start. I have no idea why the engine stopped by itself when I left it running. I have no idea what may have happened with the engine. NOTE: Before I came back to the house for the paperwork, I did stop somewhere else for a couple of minutes but the engine continued to run just fine with no problem. What has, then, gone wrong? This engine runs like a brand new XJS, sharp and powerful.

My head was not clear this afternoon. I’ll do some troubleshooting in the morning, but if somebody here has a good tip it will be much appreciated.
Thank you!

When you crank the engine does the rev counter (tachometer) show 150-200 RPM, or any movement? If not it points to a failed crankshaft position sensor (CPS).

Reinaldo …

Didf your car pass the test for a failed crankshaft position sensor as Mike pointed out ?

If it did then put in a new distributor cap and rotor. Excellent chance that’s the problem.

Check for spark from the center coil wire to ground (pull coil lead out of cap and hold close to engine ground while cranking the engine)

If you have spark there but not at the plug wires, you have a bad ignition rotor. If you have no spark at the center coil wire, move onto testing the crank sensor with a vom meter on ac current setting.

A similar problem occurred with my 1990 XJ40 (73,000 mlles) a few weeks ago and it turned out the external Bosch fuel pump had failed. Strange, as it was a replacement pump that had only lasted 2 years.

John, I was under the impression that only the 3.6L 1988 & 1989 cars had external fuel pumps and that Jaguar had changed over to the internal in-tank pump for the 4.0L cars. Is your car a 3.6L or a 4.0L car?

I’ll get to work on the car this weekend. Thanks for the tip, mate.

I’ll get to check all this sometime this weekend.
Thanks for the tip, mate

My 1990 car is a 4.0 liter. I believe Jaguar changed to intank pumps circa 1991 or 1992? They did it because with out a fuel cooler as part of the AC system they had problems with vapor lock and pump cavitation in very high ambient climates. Ask me how I know. They came up with a rather complex fix but ultimately went with the intank pumps.

Well, ignition issues here are now immaterial because the electronic fuel pressure gauge on my A-pillar and the mechanical fuel pressure gauge on my fuel rail are both telling me that, while cranking, both needles erratically move to about 2 to 3 PSI at best. So, unless it is a funny fuel pump relay failure mode, what we’re dealing with is the worst case scenario, i.e. a defective fuel pump, why? well because it is my understanding that the fuel tank has to come out in order to remove the fuel pump, right? Why couldn’t it be something a little easier, unless the fuel filter all of a sudden became plugged up?

Or, a problem with the fuel pressure regulator at the rail?

The good news is, the car didn’t leave you stranded at the side of the road. But gently let you down in your own driveway

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Check and/or swap out the oxygen sensor heater and fuel pump relays as well as wiring to pump and of course the fuses before tearing into tank. Any of these failing will stop the pump.

There should be a wiring connection on the tank that send power to the pump inside the tank. You could try jumping power direct to that connector to see if the pump runs that way.
That test would tell you if it was the in-tank pump or some external fault.

Yes, Steve and Aber. I was on my way down to check that blue/red wire from the fuel pump relay output, pin 87 that shares power with the O2 sensor heater element.

I’ve been also thinking of mechanical devices possibly messing with the fuel pressure of an, otherwise, fine fuel pump, such as the f/p regulator by the rail and maybe even a semi-plugged fuel filter, who knows.

Thanks for the tip, guys.

I forgot to mention, if you take a good look at the schematic diagram, if something may have tripped the inertia switch there would be several circuits affected, including the fuel pump relay and the mass airflow meter, but the engine would still crank but the car would never start. I’ll go check this too.


I have a 1985 XJS that originally had the 3.6L AJ6 motor (now has a 4.0L AJ16 motor) with the 5 speed Getrag trans. A wonderful car to drive. I have always wondered what the rare XJ40 cars with a manual gearbox were like to drive.

I can answer that for you - like all manual cars, a royal pain in the ass.

Just my opinion of course :stuck_out_tongue_closed_eyes:

Obviously you are not a sporting driver.

I always like to take a break from tooling about in an automatic car to drive some of the other cars in my collection and more than half are manual transmission cars.

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Not obviously at all, the XJ40 j-gate is basically a manual without the pain of clutch.