Hello fellow Jaguar enthusiasts, I am a young Jaguar owner closing in on one whole year of owning a Jaguar. While I have greatly enjoyed the challenge and reward owning a beautiful 1987 XJS, I am stuck.

This is what happens:
The car starts, runs perfectly. I take it to drive and cruise around the back-roads around my home. After about 2-5 minutes, the car begins to act weird. It seems to stutter, and not really have the response it normally does. The reaction to increased fuel is delayed, and the overall power seems to lack. There are ways around it, lightly pushing on the gas in a slowly increasing manner works, but in situations where you need to punch it, (by necessity or pure enjoyment) it doesn't react how it should.

Overall: The car doesn't seem to have the response it should to increased throttle, it lacks that instant response and will stutter. It used to stall in these situations (like coming to a complete stop, or a dramatic change in throttle) but now it only seems to struggle a bit after some modifications and cleaning.

Things to consider:
I have done countless things to this car, but as per the fuel delivery system, this what I have done (that I can remember off hand):

- Brand new fuel pump, great condition, runs extremely well.
--- When in the first few minutes the pump sounds fine, but after driving for a few minutes the pump begins to make sounds like it's struggling.

- Cleaned tank. I did a full tank repair myself, welding a plate to the bottom and coating the inside and out with special leak repair liquids.
--- Only issue seems to be the direct flow from the tank to the surge tank is lacking, but I think the power of the pump should circumvent that, I am also considering using a second pump.

- Throttle Position Sensor.
--- I did the Ford TPS modification and according to all the tests, it seems to work perfectly fine, it won't "zero out" perfectly, but it's damn close.

- General Cleaning.
--- Cleaned all the rails and paths using acetone and a compressor air nozzle blasting all the returns and feeds clear of any obstructions, it was pretty damn gross, but no major clogs.

Conclusions I am coming too:
1) Could it be the surge tank? The issue seems to be the lack of fuel coming from the tank into the surge through the pump out into the car, would a second pump help? Would bypassing the surge entirely solve the problem?

2) Could it be a leak? I can't imagine it's a big one, but the problem has decreased since cleaning, so could it be leaking?

3) Could the gas tank be clogged? Like I said, the fuel doesn't seem to travel out of the gas tank into the surge tank a sufficient rate.

What I plan to do barring no solution:
I'm just going to bypass it all, making my own simplified fuel system directly from the bottom of the tank, into a filter, pump, rails, and return.

I would love to stick with the original build of the car, but I am out of ideas on what to do.

Has this happened any of you? Any ideas on how to test this, or fix this?

Thanks so much in advance.
---Sledge.

 

You need to fix the problem. Have you tried to clean the outlet from the main tank to the surge tank? It is probably restricted with tank sealer.

 

Like Greg E says, this sounds exactly like a fuel feed to the pump problem. Basically, the pump is running short of fuel and will fail if this is not fixed. The car runs Ok for a bit because the reduced gravity to pump fuel feed 'catches up' when the car is at rest. The pump will not suck, it must have a decent gravity feed. Fuel should pour very quickly from the fuel pump feed pipe. If not, if unblocking the tank exit (this is the most likely source of the problem, considering the tank lining stuff) does not fix it, then go to the sump tank under the battery (your post does not say if you cleaned this when you did the tank or not).

If not, this unbolts and can be cleaned out by removing the slip ring fixing that holds the outlet to the pump. Also change the sock filter inside, which will be blocked if you did not change it, and check all the fuel pipes for blockages.

Finally, it is very easy to get too much of a kink in the pipe from the sump tank to the pump, which has to turn through 180°, and this can restrict fuel feed.