There is always a first time for everything. I have not used the car for about 6 months. Since my wife's truck developed a cooling issue (busted plastic radiator - hate them), I recommissioned it and she drove it for a week with no issues (50 miles daily).

I started driving it this week. Monday, no issues. Tuesday, on the way back, at some point, the throttle quit responding. It felt like limp mode but there were no warnings or lights. I coasted to the side and waited for a few seconds. The engine was running so I put it in gear, took off and finished the remainder of my 25 mile trek.

Today, again, on the return leg, same issue. This time I paid attention to the RPM gauge. The needle was not moving when I pressed the accelerator pedal. At some point the engine died and was barely able to pull over. I was on a tollway right at an overpass. Pretty darn dangerous when folks are literally zooming by at 80mph or more inches away from you. I attempted to restart the car. It wanted to catch but never did. I called AAA and the police for cover and took an hour for them to get to my spot. During that hour I did try numerous times to restart the car but to no avail.

I had the car towed home and after about an hour I attempted to start it and it started right up. Again no engine light came on or anything. I did not have a chance to pull the codes (if any) yet. The symptoms seem to me like classic fuel starvation problem (pump(s) on their way out).

Any similar experiences out there?

 

Just thinking out loud here:

I think that your fuel pump idea is a good place to look, but I think that I would check the fuel filter first. It seems to me that a almost clogged filter could cause the problem.

 

Ok, I should have added some more details. Less than 200 miles ago, I replaced fuel filter and spark plugs (plus spark plug seals, valve cover gaskets etc). I do not think that is it (unless I got a defective filter). I just hope I can duplicate the issue w/o having to drive the car. I will hook up a fuel pressure gauge and let it run and see what happens. It will take a few days to run the tests.

 

Do you have a fuel pressure gauge? or you can take the little blue cap on the fuel rail off, and press the stem down to see if fuel sprays out, I would try this right after the car dies. These cars don't usually throw a trouble code if the fuel pump fails, even though you'd think they would. Being that you have an early XJ350 Supercharged, you'll have 2 pumps, one on each side of the fuel tank. Try checking for fuel pressure first and see what happens.

 

Since the incident described earlier, I decided to park the car and not use it. No need for the aggravation on whether it will let me stranded again.

The other day I had to back it out of the garage to get to my lawn mowers and stuff and let it run for a while as I normally do with semi-dormant cars. After a while, it shut down. Only this time, it did not restart, not later, not the next day. I pushed in the shop and hooked up a mechanical fuel gauge. No fuel pressure whatsoever when the ignition switch is on. I hooked up my SDD setup and the only relevant code that was stored was P1235 with an explanation of "Fuel pump control out of range". I looked in the service section but did not find a way using SDD to turn on the pump to see if it makes noise (or not). A set of fuel pumps for this XJR is around $2K.

Trying to figure out if there is a definitive set of steps that will allow me to quickly test whether it is the pump's fault or the fuel pressure regulator or the electronics module that is at fault.

I have taken the pumps out of this car before and it was a pain in the ***. I took them out due to a faulty check valve.

Anyway, that is my next project. Will time slice between this and getting the carburetors tuned on my Mark X.

 

The fuel gauge in the instrument cluster reads about 1/4 tank full. I removed the rear seat today and opened both fuel pump cavities where the fuel pumps are mounted. The right hand side of the fuel pump was bone-dry empty while the left hand side was full. It looks like the fuel transferred from the right hand cavity to the left hand side cavity and stayed there.

Or, the left fuel pump failed and the right hand side pump was fueling the car and when that cavity dried out, the car died. I could put gas in the right hand side cavity and see if I can get the car to run. That would confirm the left hand side fuel pump died, no?

 

I did just that. I put gas in the right hand side cavity, sealed the cavities (had a hell of a time getting the fuel pump plastic nuts to catch) primed the pump and lo and behold - I got pressure and the car started and idled just fine.

So the diagnosis is driver's side fuel pump failed.