First check no-one has installed a bypass pressure valve on the pump (if in doubt take a pic + post it here)
Second - these gadgets get easily confused. If the pump is cutting out after a few seconds I think the controller could be in a bind, I've had exactly the same problem and there are other posts about it.
I think it's to do with the sequence of events involving the top latch switches and I think (pure conjecture from listening to the pump note) it gets into a state where valves are opened or closed so the pump re-circulates the fluid, just the same as if the petcock was open.
I eventually cleared mine by manually opening the latch (petcok open) then closed the petcock and used the switch to lower the top.
When it raised everything worked fine and has continues to do so.
You've nothing to lose by forcing a few cycles with manual help if needed because the only other answer, I fear, is a dead pump.

 

Earlier this year, on the "other" forum, there was a post by JagDoctor giving this when-all-else-failes procedure for screwed-up convertible tops.

To reset the system, press the top switch and lower the quarter windows.
Open the valve on the trunk, counterclockwise.
Release the top latch with the allen wrench.
push the top cylinder pistons back and down until they go over center, about 2 inches.
Lower the top completely by hand.
Close the top latch with the allen wrench.
Close the pump valve and press the top up switch.
It should go up and latch. If it doesn't, there is a permanent problem

A later poster said it fixed his problem, which had resisted many other attempted remedies.

I've got no 1st hand experience with this. Just reporting what was said.

 

Dennis,
I tried this but all the grunting and swearing I could apply wouldn't unlatch the lift cylinders so I used the pump.
That's what made me think it is the sequence of events coming from the top latch lock.
Worked for me!

 

Yeah, I expect there are some other variants that might work too. The whole system is under the direct control of Satan, so this could change from day to day.

 

There's no doubt about that. I'm amazed Lucas Prince of Darkness doesn't have a component or two in there.

 

Thanks to Gus spending so much time with me on the phone, we were able to lower the top manually.(Thanks Gus) He asked me to exercise it a few cycles, maybe he meant exorcise....
Here is the update:
When it closes, everything works perfect. It raises strong (I can’t hold it back against the pump pressure), it latches and the rear windows raise. Lowering is another story.
It unlatches but doesn’t have enough pressure to the rams to lift the top. I jiggle it up and lift hard to start it but I can hold back and stop travel anytime as though the fluid is bypassing internally. And the latch never retracts.
Perfect up and very weak down.
Does anyone know where I can find the hydraulic schematics? I may have to make a trip (90 miles one way) to the dealer.

Thanks to all for trying to help, Gary

 

Here's the plumbing
JagRepair.com - Jaguar Repair Information Resource
I wonder if it's just one of the solenoid valves sticking.
It seems as if your pump must be OK.

 

He gives you the que3stion's answer first. Then it's up to you to accept it and pay for it. If you are disappointed in the answer, II beleive you don't have to pay, but they keep a record on you and if you ask them , get answers, and stiff them, they refuse to answer any more I think. I don't reall
y now, since every time I've asked a quaestion I get a good answer.

 

The rams are inherently stronger (more force from a given amount of pressure) when expanding (the raise-top direction) than in the reverse direction.

If the piston seals in the rams were starting to bypass as you suggest that problem should show up first in the lower-top direction ... what you're seeing.

These guys have rebuilt rams for several people here. All were pleased, I think.

Turning a dealer loose on this problem could be big bucks.

 

Here is the electrical troubleshooting guide for the top: http://www.jagrepair.com/images/TSB/XK8/501-11am.pdf

 

The roof is operated by the same pump in forward and reverse the only difference is that when it opens it is trying to lift the roof that is extended forward like trying to lift a broom from the floor with one hand at the end of the handle. It is difficult but can be done and in this situation linkage is working to make it easier. At this point I would suggest having the battery tested. I know that you operate it with the engine running but would like to see what the test provides. I should say that few on the forum have experienced a slow open operation over the past several years.

 

Yes, well. I think this is plain-vanilla stuff, but just to clarify:

If the pump produces, say, 500 PSI and the ram's diameter is, say, 1 inch then the force when expanding the ram is just pressure x piston surface area = 500 x PI x (1/2 squared) or about 393 pounds.

If we have the same 500 PSI available to compress the ram, the resulting force is less, typically much less. This is because we're no longer pushing on the full piston area but only on that part of it not occupied by the push rod. So if the pushrod diameter is, say, 3/4" then the force is ... 500 * [PI x (1/2 squared) - PI x ( 3/8 squared)] or about 220 pounds.

I don't think this is at all controversial, but I've been surprised before ...

 

Don't we have thread for this stuff?
You'ld also have to consider the mechanical effort for opening and closing.

 

"this stuff"?

Gary's problem is that things are good in one direction, not so in the other. Noting the different forces produced in the rams -- which might explain this -- belongs elsewhere?

 

Gary,

Call me any time you have my number.

 

I am waiting anxiously to see how this eventually resolves When it comes to these cars it seems that when someone posts a problem, more often than not the same problem will eventually come up with the rest of us.

Still waiting for some adventurous soul to resolve the rear window adjustment problem I posted elsewhere (again, seems common to many other members here).

Doug

 

Their practice is (or was) you asked the question, they asked you if they answered it satisfactorily, would you pay x dollars, and if you said yes, they would answer it and then ask you iif you were satisfied- and if required , further discussion led to te satisfied position and then you paid. The costs depend on desired complexity. If you want the sheets or reference out of the repair manual attached, it is $45.00, otherwise $29.00. Since jaguar dealers here charge $125.00 an hour for diagnostics, I felt the justask peoople were a goood deal. That was of course in my preforum days. I now would come here first and then only if peoople here were stumped would I then go to justanswer.com. So it's really more of a no charge than a refund if you are not satisfied. They also tell you what reasonable repair biills would be from the dealer.

 

Depending on the height of the roof when it is released the roof itself could be making contact with the micro switch resulting in the pump not coming on to lift until the roof is pushed up and away from the header. How far do you need to push the roof open? If it is enough for the roof to just clear the latch then I would be looking at the latch and the attaching mechanism and micro switches.

Link: JagRepair.com - A Jaguar Repair Information Resource

I hope this helps.

If it works the service is still free.

 

Success!
At least I am back where I started, the latch still doesn’t retract with the top fully down.
Apparently the pump pressure can bypass through the latch if it isn’t in the correct position when lowering the top.
Thanks to your page Gus I got my nerve up and pulled the trim from the windshield header. I cleaned and lubed the mechanism, it moved much freer with the by-pass valve open. The top goes down strong now and there is no way I can hold it back against the pump pressure.

Once again, I would like to thank everyone for taking interest in my problem and for all the helpful suggestions.

Thanks to all, Gary

 

Well, it looks like I spoke too soon, it’s up to it’s old tricks again. The top worked perfect 5 or 6 times and even retracted the latch one time which is the only time I’ve seen that happen.
It still seems to be an internal bypass of fluid. During one malfunction the top lowered correctly and then came up with little power so it can slip in both directions.
I think it might be the latch solenoid/valve not operating fully. Does anyone know if that would let the pump pressure bypass through the stuck solenoid?
Next question, does anyone know if the two solenoid valves on top of the pump are identical so they could be swapped to see if the symptoms change with the solenoid?

Thanks again, Gary