I’m posting this here because the ’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!

 

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.

 

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 worst case scenario? 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? I don't think I'm ready or looking forward to removing the fuel tank from the car. BTW, I did remove the fuel tank cap to release possible vacuum build up - no difference.

Anyway, I want to thank those who responded with tips, it was much appreciated.

 

Or, perhaps a problem with the fuel pressure regulator by the rail?

 

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.

 

That would be the blue/red wire from the fuel pump relay output, pin 87, that shares the power with the O2 sensor heater element. That's what I'll check next because I want to confirm that the fuel pump is, indeed, getting the power and how solid those 12 volts really are. Plus, I still need to check some purely mechanical things that may be messing with the fuel pressure from an, otherwise, fine pump. If there may be a problem with the f/p regulator at the rail or, ultimately, is my fuel filter semi-plugged? Men, so many things involved in the operation.
Thanks for the tip

 

Hi Reinaldo,

Sorry for the late reply, and sorry to ask a simple question, but is it possible your fuel level sender has failed, indicating fuel in the tank when in fact there is none?

Cheers,

Don

 

Thanks for the response!
I had just filled it 2 days before this failure. In fact, I've been wondering about my bad luck, as now I'm facing the draining of a full tank to remove the pump, bummer.

 

My luck has been pretty consistent: whenever a fuel pump fails, the fuel tank has just been filled up!

 

Well, since it appears to be a fuel delivery problem, I decided to go straight to the fuel pressure source. I went and applied +12.75 vdc to the f/pump relay output, pin 87 where it connects to the O2 sensor input wire, pin 2, which BTW is a blue wire and not red/blue like the Jaguar manual says. I could hear the pump running, but my fuel pressure gauge on the fuel rail went up to only 6 PSI and it stayed there for as long as the power was applied to it and not any higher. To make sure that all electricals were correct, the voltage, when applied, went down to 12.6 volts (down from 12.75) and the current that the running pump was drawing was 3.45 amp.

The only other possible issues could be with the F/P regulator. I wonder what is the status of the fuel pressure regulator when the engine is not running (no vacuum applied to its diaphragm. And, maybe the filter is plugged up. I believe that I may have a new filter in my cabinet somewhere.

The pump is running, but it's not capable of building up to the 40 PSI it's supposed to with proper power applied. Oh man, change the pump?

 

Well, that's what the Jaguar schematic diagram says, but when I went to apply the 12 volts to that spot to make the pump run, it shows a plain blue wire with NO red. And BTW, not the first wire that I find the actual wire on the XJS to be different from what the diagram indicates.