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!

 

Maybe start with the very obvious,

Is the Fuel Pump running with the ignition first turned on?
Have you got a spark at the plug with the engine being cranked?
Is there excessive vacuum in the fuel tank? Open the cap and see if you get a sudden whooshing noise.

Good luck

Paul

 

Vacuum in the tank...

Seems t be a thing these days, eh?

 

Paul, Scott, I will be checking this, hopefully during the weekend.
Much appreciate the tip!

 

Read my thread just below.

”1996 xjs won’t start

Lots of information and help from the forum.

Good Luck

Softball60/Paul

1996 xjs, 1957 XK140 Drop Head and every other British sportscar know to man...(maybe not all)

 

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 pressure 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?

 

gauges are unreliable in cranking mode, as they are not getting proper current. I would do a physical test of fuel pressure before tearing anything apart. Even if it is just removing a feed pipe and seeing if there is a huge jet of fuel.
FPR change is also a good idea in any event.

 

My mechanical gauge at the rail confirms the low and erratic f/p reading of the cockpit electronic gauge, but what you say, Greg, makes total sense, so, the first thing I'll do whenever I resolve this problem will be to read both f/p gauges when normal cranking, just to confirm.

 

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.
At least this tells me that the relay and the pump are all getting the power they should be getting.

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?
.

 

If the pump is running, I think it far more likely you have a filter or FPR problem. Pumps usually either run or not.

 

There is a strainer in the lower sump tank that could be plugged, a discharge filter after the pump that could be plugged. The problem is that if the engine is not running you should be able to cycle the key a few times and see solid fuel pressure without the engine running. To me that points to the regulators or pump. If there is a way to pinch the return line to the tank you can see if pressure increases or not.

 

Is it possible to see if a FPR diaphragm has failed on the new cars by seeing if fuel is ending up in a vac tube... Again, I don't know these cars well, to even KNOW if the FPR is operated by vacuum...

 

On the later XJS the FPR has a vacuum connection

 

I have heard wise folks here give the advise that a running pump doesn't necessarily prove that it's a pumping pump. You might need to change it...

I have a hard time understanding how a running car could go to a non running car in the few minutes you were away from it due to a clog that brings rail pressure down that low that fast and as permanently. If possible I would be trying to find a suitable bucket or container, a line of hose and a way to connect that to the fuel line that feeds the rail. Hose in the bucket and jumping the line to confirm that there is or isn't fuel.

 

Hi Forcedair

I've had very similar situations, where once panic starts to set in over what might be, then logical thinking sometimes goes out of the Window as the one possibility that hasn't been touched on yet, it the Fuel Pump Cut-out Switch in the little plastic box down by the Passenger door jamb

The Plastic Box with the Hole in the Top, where the Switch might need resetting by pushing the Plunger inside it down with the end of a Pencil, which should be the number one thing to check but often gets overlooked and I can't remember the number of times that I forgot to do that

Inside that little Plastic Box is a Magnetic Switch, where depending upon how it feels on the day, even a bump or a Pothole could trigger it off

Also don't overlook the fact that you could be low of Fuel as on an XJS 4.0L you need about 10 gallons of Gas just to cover the Filter on the bottom of the Fuel Pump

In a worse Case Scenario, if you have to Change the Pump, you don't have to pull the Tank right out of the Car but just far enough back to get to the round plastic 'thingy' (aka the evaporator) which is held in place by a Big Locking Ring

I only took the Tank right out because I wanted to Clean it but even so changing the Fuel Pump is still a PIA job at the best of times

How to Change the Fuel Pump on an XJS 4.0L

Almost every trick in the book to get an XJS 4.0L engine to Start

 

When I applied direct power to the pump itself I was bypassing the inertia switch and that's when I heard the pump run with no strange sounds and the pressure at the rail went no higher than 6 psi.

Also, remember that I had just filled her up some 20 miles before this happened, so the tank is full.

BTW, somebody hit my XJR at the rear left door while I was standing next to it at The Home Depot parking lot; I'm very lucky that I still have my legs. So, I'm going to have to put my XJS effort aside for a bit to take care of a few things. I much appreciate all the help from all of you guys, this forum is incredible!

I'll get back here as soon as I do something.

 

BTW, my XJR is kind of like your XK8. It's a 2002 and in beautiful Zircon color.

 

If ya meant me,,,, oh THAT car, lol

I LOVE the car but,,, I am having a real problem with the subframe... The steel long bolt for the upper control arm has inevitably worn out the cast aluminum pivot point of the subframe. A really really stupid design, but hey. Ya know. When that car is cruising (and when the roads ain't bumpy - rare patches in NYC), top down, nice weather, there is nothing quite like it. That is, cept the XJS, lol...

Then I have a few other things. But yes, I love to hate her.

 

Same happened to me. After six weeks and much checking I called over a mechanic. Checked spark. I had spark but not as strong as it should of been (apparently). Replaced the coil and problem was solved. It sucks when you check spark, you have spark but the car won't start because the spark isn't as strong as it should be.