So my 90 got a Bosch 69536 pump, new hoses including the feed from the surge tank which has a spiral hose saver on it to prevent kinking, a verified clean surge tank and strainer 10 months ago, and at the 103F temps we've been having the pump is screaming and you can feel the outlet hose has air pockets and inconsistant fuel through it.
I assume this is due to the sump tank and pump being 120F or better after a quick jaunt into town and back, let along an hour or two at 75 on the interstate.
I don't think this system is up to these temperatures and it was a bad idea to mount that pump in the trunk vs under the car where there is airflow like virtually everyone else in europe did, it also should have had a lift pump in the tank but I get why they thought they could get away without it having it so near
the surge tank. Until it's 103 degrees out. There are a ton of other people with various other similar Bosch equipped vehicles that have similar issues if you google around a bit. Some find a restricted supply side, some never seem to find an answer.

Full disclosure, this is feeding an LT1 that is rather known for heating fuel up and there is no fuel cooler but I don't think it would be enough if there way unless it was a heeeeck of a lot more effective than I think it is.

So, I've got a bad pump or this system isn't viable at these ambient temps.
I ordered another pump and I'll try it but I'm not hopeful.

Tell me this, why wouldn't one mount a modern in-tank pump IN the surge tank today in 2023?
It looks like there is room and I don't see a downside?

Or, add a lift pump in the surge tank.

Or, replace the surge tank altogether with something like this.

I'm favoring the submerged in-surge-tank pump idea.

 

In my opinion you hve a feed problem from the main tank down to the surge tank and/or a problem feeding the pump from the surge tank.
In a standard, working correctly, pre-facelift main tank/surge tank/pump setup there is absolutely no possibility of the pump running dry if there is any fuel at all in the main tank. The main tank, if you disconnect the feed from the surge tank, will deliver 20gallons into your boot (trunk) in 90 seconds.
It is common for the hose to the sump tank from the main tank to decay internally and it should be replaced with a 1/2 in diameter moulded one.
Change the filter and blow out the delivery/return lijnes to the engine bay.
If your pump is screaming it will soon fail, so replace it once you have done all the above.
My car performs properly on 100°F no problem at all (factory V12 engine).
Maybe Post a photo of your setup so we can see if anything loks odd?p

 

I agree with Greg.

The standard system is fine down here, even in our 44+ C Summer temps.

The gravity supply is highly suspected by me.

The pumps I use are Bosch or Goss, and that probably means zero to the people up there, as do your numbers/brands to me.

The main tank supply spigot could be partially clogged with main tank debris, thus restricting gravity supply.

Remember, these pumps are NOT suckers, so gravity "head" supply is critical.

AND

Main tank venting is also critical to that gravity supply. If in doubt, put the tank cap in your pocket., go for a drive, see what eventuates, maybe nothing, but at least it can be crossed of the list.

OH, I dont run coolers on any of my V12 beasts, and no issues in 30 years.

 

Okay, I'm open to that. Is there a gpm flow test for the feed to the surge tank to be done?

 

Never tried or thought of that. I be a very simple old guy.

Over thinking hurts. A 1/2" hose is going to flow a heap in a hurry, think of a garden hose syphoning a drum of water, its the same.

A bloody big mess in a hurry if that hose ruptures, or you forget to clamp it off before removing the fuel pumps, oops for me too many years ago.Never forgot again.

The insiide of that tank is an unknown, so debris will be there, fact, but how much is the question.

Drain the system, via the drain spigot of the sump tank, remove that main to sump hose and compress air blast it back into the main tank, Reconnect, refill, and see if there is a short reprieve of the issue. Tank out and clean is a "normal" list thing at 33 years old.
The plastic filter on the end of the sump tank outlet pipe (the one TO the pump Inlet) is well documented as clogging, and the part number changed a few times as "updates" were tried. I doubt they ever solved it, and went to In Tank pumps not long after your car was made, and they had their own issues also.

 

The reason I don't particular think it's a lack of fuel in the surge tank is 10 months ago I pulled the surge tank when I installed a new fuel pump and observed it having a reasonably small amount of larger rust chips in the bottom and the strainer screen being perfectly clean.
That tank had never been out before and the fuel pump was original (and working but a little noisy) at about 230K miles at the time, I replaced it mostly as a preventative measure. This car has never sat with old gas in it as many do.
That and this problem only came up since the weather has been so hot, and an IR thermometer on the surge tank and pump show them north of 120F. That's plenty hot, since the pump internals will be hotter, to start to cavitate.
A restriction or lack of fuel can contribute for sure, but I'd be surprised if that's the case. I think this motor with the aluminum fuel rails in contact with the intake the way they are is heating the crap out of the fuel this time of year.

When I changed the pump I used the old pump to empty the fuel into containers once the tank was fairly low, seemed to flow fine.
I assume if I take the feed to the surge tank and run it out of the car into a container it it gravity flows fine, that would indicate that it is fine?
I also have an endoscope I can run in there and look around. Somewhere I saw the internal piping of a fuel tank but I can't recall where I found it.

A small modern fuel pump mounted in the surge tank sounds like a win-win to me but it won't help if the surge tank isn't staying full.

 

Had my thinking time, and here is my thought.

Your market and mine are worlds apart on emissions and tank venting, so be it, the basics remain.

If that sump tank is NOT remaining full, the breather from that sump tank to teh main tank is not breathing. Ours went to one of the 3 spigots on the top RH corner of the main tank, I think?

Its been years, so look and follow that small hose from the sump tank.

It may be that simple.

 

Grant is referring to number 14 in this diagram
https://parts.jaguarlandroverclassic.../brand/jaguar/

 

I think the vent tube on mine is next to the outlet to the pump but same principle.

 

So why is there a vent line (the smaller one with a spring clamp on it) and a return line (I assume the upper of the two larger ones).
Fuel flows freely from the surge tank vent line nipple fwiw.

 

Thanks for the photo which I have marked up.
I = the vent tube, check that this is not blocked by removing the spare wheel etc and undoing it and inspecting it
II = something that UK spec cars do not have. See where it goes to and if anything there is blocked. It may go tothe main tank as well, but I have no idea. But it looks like part number 22 in the extra diagram on this page. I have no idea how it works, but someone will chime in and tell us!
https://parts.jaguarlandroverclassic.../brand/jaguar/
III = the locking ring. Carefully knock this anticlockwise, having drained the tank, to see if there is a filter blockage of loads of rubbish inside the tank.

Empty the boot first! Good luck.

 

The extra hose is apparently from TSB JLM2163 which is:KEY POINTS:

"SUMP TANK VENTING KIT

To prevent XJ-S coupe engine hesitation caused by fuel vaporization during high ambient temperature/low fuel level conditions, a sump tank venting kit
(JLM 2163) is available through Zone Parts Departments.

With the kit installed, there is a vent directly from the vapor separator feed hose into the sump tank to prevent fuel vapor from being drawn into the
main fuel system."

 

Took a detour to the evap canister since nobody has laid eyes on it in over a decade, rochester valve was semi working so I replaced it and re-engineered things into proper functioning.
Never was any vacuum on the tank but more pressure than I wanted sometimes, all fixed now.

Fuel pump is still a bit noisy, and then very noisy and you can feel the outlet hose thumping randomly with air pockets after a long drive when it's hot out
and the fuel temp goes up.
I have another Bosch pump to swap out sometime this week.

Question, while I consider it mighty unlikely in this case what does one do to test for proper flow from main tank to surge tank?
The surge tank is full, I know this since you can pull the little add-on vent line (#2 greg noted above) and fuel comes out happily and that line stops right inside the top of the surge tank.
I guess just let it run into a container from the main tank and see how much it flows?

I think I'm going to install a modern in-tank pump IN the surge tank at some point, one of the common form factor walbro style everyone has used for ages.
That should take care of any cavitation and/or pump cooling issues.