Strange no-start behavior

Driving a vintage car with a manual transmission and doing it well gives one a sense of accomplishment that is certainly missing from driving an automatic equipped car.

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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?

Definitely change the filter first. If no change, do you have a way to check the fuel pressure by tapping in (a) between the pump and the filter and (b) between the filter and the fuel pressure regulator?

As crazy as this sounds…HOW MUCH GAS IS IN THE TANK and in the tank when it stalled?
Running constant LOW FUEL will BURN out the pump . Its a super suction draw , with low fuel it strains the pump.
Another is low fuel ,crap in the pick up or screen, causing the restriction THEN BURNING OUT THE PUMP.
Theresa theme here!

Been there done that. Not difficult, just a lot of things to do to get the empty tank out. When you are confronted by the pump housing canister, post again for additional guidance. Pumps are fairly cheap and no point buying the pricey one, almost all of them are re-boxed Walbro pumps even the ripoff Bosch.
Oh and buy a fluid transfer pump, no point getting an old-school siphon lungfull of gas for a few buck fluid transfer pump. Oh and you’ll need a pair of 18" long needlenose pliers if the xjs is like the 40

I think I’ll just go ahead and change the filter, since I believe I may have a new one from a previous “no-start” problem…

BTW, and unfortunately. . . I had just filled her up, so I’ll be pumping enough fuel out.

Hello Reinaldo - when you had just filled up, was this shortly after the fuel truck had just replenished the station fuel tanks - generally there will be a lot of sediment disturbance within the station tanks, from the filling of the station tanks, which then may well transfer to your tank when you fill up - usually waiting a few hours, or the next day, helps avoid this - Tex Terry, II - 1991 XJS V12 Classic Coupe, 1986 XJS V12 Coupe - sent 10/12/2020 2220hrs. EDT USA.

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Ol so it was just filled then driven correct?
How long was the tank low?

Im asking for a reason…
What we have seen , if the tank has been low the pumps internals dry out and crumble.
Also when they start deteriorating and a full tank of gas the crap on the bottom mixes with the crud and clogs the pump screen and burns the pump out under strain.
Will it start at all after cold?

Give the tank a good whack with an axe-handle/baseball bat etc.

If the pump is the problem, usually that impact will impulse the pump motor past it’s dead spot and allow the motor to spin up again.

Only a temporary “fix” but sometimes enough to get you to a garage or back home - just remember to keep the engine running once it starts!

I couldn’t possibly tell when the truck last filled that Shell pump. I didn’t see any trucks around and I really hardly ever see any fuel trucks around when I fill.

What would it mean “driven correct”?
Probably a week and probably no lower than 4 gallons

It has been starting cold just fine. This is So Cal near San Diego and near the water, best weather in all of USA, including in early mornings, which lately has been in the 50’s F, 12 - 14 C. Most likely not an issue.

You lose both ways
If the pumps sit in ethanol gas for Lon periods it eats it up
If it’s dry they crumble
I’m betting on the pump!

Ok sediment might be sucking up and the more you run the screen gets clogged
Your getting spark
This only happened once after a fill up?
If so run the car out
It’s gas or the pump
You don’t have a cracked cap take a peek a boo

I’d ask, how often do f/pr. pumps do run fine but fail to put 40 PSI at the fuel rail compared to how often failed pumps are actually dead, as in burned or frozen? My pump is running but just not putting 40 PSI at the fuel rail, in which case, if the pressure is not building up to what’s supposed to be with a running pump, I may have some restriction that’s not letting the pressure at the fuel rail get up to 40 PSI. Suspect(s): fuel pressure regulator and fuel filter. (I admit this is in the vicinity of wishful thinking…LOL…), but it does make sense, doesn’t it?

It does, if you love this car its 30 years old!
I would change it all…
Its funny before an xj40 a series 3 would fall apart in the driveway and never make 10 years on the road…even though the xj40 had its issues, its still a tank .
Change it all, it doesnt cost much. and your set for 30 more years!

Reinaldo …

Just a little philosophy about owning a 3 decade old luxury car …

  1. If you have no mechanical ability but money is no object, and the Jaguar isn’t your daily driver then go for it. You can take the car to you mechanic for every problem and you don’t care what it cost or how long it takes.

  2. If you have average mechanical skills and can afford the parts then go for it. There’s a great sense of accomplishment doing your own repairs and you’re driving a luxury car.

  3. But no matter what your skill level if you can’t afford the parts (and even after-market parts for a Jaguar always seem to cost much more) then the car will break your heart.

When you crank the engine over and it won’t start have you tried loosening the fuel filler cap to test if you have a vacuum forming in the tank ?