Hi Afterburner

That was mega useful information!

And its looking like the Ethanol may be the cause of these Pumps wearing out a lot quicker than you would expect and maybe the In-Tank Fuel Pump is cheaper to manufacture

The only downside being that replacing it can be a nightmare unless you want to get a 'Shop' to do it, which I don't and so I will weigh up the options over the Weekend

Thanks for your help

 

It would not. The feed has to be out of the bottom of the tank for a gravity fed pump like the pre facelift/sump tank system. The point of the in-tank pump is that the entire system is pressurised from the tank forward, so when the injectors open on acceleration there is no lag. In effect the pre-facelift system IS an intank system, in as much as the pump is at the lowest point and is gravity fed by a big diameter pipe, and after it the system is (as far as the injectors are concerned) seeing only pump pressure.

If you had a pump being fed by (in effect) a syphon tube, you would have a very distinct lag on WOT. I once actually converted an intank Range Rover to an external pump - for all the reasons you are discussing - and it had lag on hard acceleration as the injector pressure dropped momentarily. I cured it by using a length of 1 inch diameter soft-walled rubber fuel pipe from the tank (syphoned through a vandalised intank pump just as being discussed). This was in effect a reservoir with flexible walls, and it collapsed enough on initial WOT to feed the pump and thus the injectors until the syphon feed to the pump caught up half a second later! Without that pipe, the pump could pump fine, but it could not suck as fast as needed. The difference between 15 psi air pressure and 5 bar pump pressure from the tank onwards means throttle response lag unless fixed somehow.

 

Hi Greg

Cheers!

Looks like I may have to rule out the Pre-Facelift Pump option

But something you said earlier about the In-Tank Fuel Pump for the V12 and the Straight Six being the same has got me thinking that an In-Tank Fuel Pump of 130 LH might be enough to run the 6 cyl

 

It seems to me the biggest deterrent to the in-tank pump is pulling the tank out to remove the pump. I think it would be much easier to remove the back seat (coupe) and then the shelf. From there remove the pump. I am unsure about attachment of the pump, I assume it is somehow attached to the front of the tank. The second consideration would be the choice of pumps. Would you go Jaguar (shades of Lucus) or would you go big bucks on a different pump? I feel the complications of reengineering an outside pump does not warrant the trouble. Albeit Jaguar is noted for some of its Rube Goldberg solutions, I choose not to join with them on a fuel pump replacement.

One thing that has not been discussed is the introduction of a fuel additive that would be helpful to the motor as well as the pump. I think Esso or Chevron has Tecsomething in its fuel that is supposed to clean and lube the fuel system. Maybe in the long run that is the way to go...

By the way Jaguar Forum THANK YOU for the 90th birthday wish... it was appreciated!
















9shades of Lucus 0 or would you

 

Hi Afterburner

On an XJS Convertible like my 1995, there is no way to get to the Fuel Pump except by pulling the Tank out and no Parcel Shelf that you can cut any holes in

As for pulling the Tank out, that can be a bit of a 'nightmare' as the Tank is behind a Steel Baffle with some very awkward nuts and bolts to undo, especially around the battery compartment

And you also have to take out the Hydraulics for the Soft Top and numerous pieces of trim that need unbolting, in a 'Nutshell' everything but everything seems to be in the way

Then of course you have the very flimsy plastic sleeve which goes between the Fuel Filler and the Neck of the Tank, that is almost a Shrink Wrap Factory Fit, that absolutely does not want to come off

Not even after days of trying everything I could think of including lubing it with Washing Up Liquid

The only way to remove it was to cut it through with a Bread Knife, only to find a replacement is about £80+!!!!!!

This is a PIA Job if ever there was one

Belated Birthday Wishes

Alex

 

Thanks!
0ne other solution nobodies mention. You could but a separate tank in the trunk and connect it to the OEM tank. The plus would be to double your range (Good when chased by police!) New fuel pump accessible in new tank. Downside loss of trunk space, extension of under car fuel lines, and rear end collisions.

 

No need to do any of that (insurance company probably wouldn't like it!)

I've already got the OEM Tank and the OEM Fuel Pipes all the way to the Engine Compartment, with the Return Pipe already plumbed in

So all I need to try and do is to Gravity Feed a Pre-Facelift Fuel Pump for a V12 and then Connect the Outlet to the Engine with a couple of wires from the Fuel Pump Relay

I am also planning to move the Fuel Pump into the Engine Compartment

Can anyone see a reason, why this wouldn't work?

 

Yes, the reason is simple: it will drain and take a while to suck fuel all the way to the front. Even diesels with their main pressure pumps in the front have an intake pump to pre-pressurize the system to avoid the main pump running dry. The longer the suction line is, the more prone it is to sucking air rather than fuel and that will lean out the combustion... That is why companjes pressurize the lines. A fuel leak is easier to find than a vacume leak. Same goes for fuel lines.

My old Volvos had a fuel pumpunder neath the drivers seat under the car. If the intank pump failed, wbich was required for the start up, the engine would start really bad. Sometimes not at all, as the main pump is sucking over such a long distance.

Oh, and it is a bodge... Just saying. I wouldn't bodge a precious gem.

 

Hi Daim

While I get what you are saying, the Fuel Pump from a Pre-Facelift V12 does not do any Sucking as it is Gravity Fed and so it would be Gravity Fed from the Fuel Tank, even if I put the Pump in the Engine Compartment

Providing the Pump was lower than the Fuel Tank, so not sure why you say that it won't work?

As for being a 'Precious Gem' that would be one of the last things that you would be calling her, if you ever had to change the Fuel Pump on one of these

 

OB
If you could run a gravity feed from the bottom of the tank down to an external pump in the boot, via a swirl pot, and then connect it to the normal undercar flow pipe 9ie reproduce the pre facelift system) it would be OK. How you get a spigot into the bottom of the tank is not obvious though. A fuel pump in the bottom of the engine bay (ie below the tank bottom) is NOT a good plan, for Daim's reasons, for safety, for the fact that the suction-feed to the pump would be a big problem unless you used a wide and soft-walled undercar feed pipe (also safety, insurance etc etc problems). The problem is that AFTER the pump fuel is being pushed at 5 bar to the injectors; PRE the pump it is being pushed TO the pump at 1 bar plus the weight of the fuel in the tank. It will not feed the pump sufficiently on sudden demand.
Can a pre facelift fuel tank fit in the space you have your current tank in? That might be the easiest thing, if the insurers OK's it.
But like the famous nipple, the best thing is to get stuck in and fix it properly, in this case as per OEM! (as I am sure you know in your heart!)

 

Hi Greg

Nailed it as always!

But I don't know if a Pre-Facelift Tank would fit, that is something that I will have to look into though taking on-board what you have said, maybe I'll give it one more go with an In-Tank Pump

Its just a shame that Jaguar changed it, which turns a previously simple job into a bit of a 'nightmare'

Though another idea might be to have an easy to get to Sump Tank with an In-Tank Pump in the Sump Tank

Maybe not this time around but what do you think about that?

 

A sump tank in the boot would be fine, but it would still need to be gravity fed, and would still need a breather to the main tank (as per OEM pre facelift setup) so would take a bit of fettling...
Did pre-facelift convertibles have the sump tank arrangement? If so a scrap one of those would provide a decent kit. or something to copy, anyway. For all I know the convertible pre-facelift tank might be the same as the coupe.
I reckon the bolted in bulkhead panel is a strengthener, and that would have to go back in, even if a few holes were made in it here and there!

 

Do as you wish... I was giving you my doubts and they are still there.

Oh, and changing a fuel pump: if that is one of your limits, then I'd pass it on. I've changed two fuel pumps on the X308 series. The same tank installation. Even worse: it is really awkward to remove. The job took me about 3h incl. removal and refitting of the tank. Instead of doctoring AROUND the problem, just solve the problem. That is solved by removing the tank and changing the pump. It is not complicated. Just fiddly.

 

Hi Daim

I've always thought the In-Tank Pump was a really Bad idea, especially when they got it right the first time

 

Hi Greg

The Sump Tank on a Pre-facelift Convertible is the same as on a Coupe and I have got a Spare one I could use, although I would have to mod the Tank quite a bit, so may not be worth doing at the moment

I've also got a Spare Pre-facelift Tank in good condition but don't as yet know if it fits

As for the Steel Bulkhead, that would have to go back to stiffen it up as you say

The beat goes on......

 

That's the thing: the in tank pump is actually the better version. You have less hoses. Less chances for a leak to occur. With an external pump ypu have: hoses from the tank to the swirl tank. From the swirl tank to the breather and also to the fuel pump. And as stupid as it spunds, every hose connection is a leak possibility. Most in tank pumps connection straight up to a press fit steel pipe going to the front. And then back.

Imagine you park your XJ-S with external pump. Over nigut the slightly perished hose before the pump becomes fully perished. Your entire tank fill of fuel will empty itself into your boot.

That happens, which is why the in tank pump was introduced. That can't empty itself unless the tank has a hole. Rubber is more likely to leak than metal.

 

And your driving along miles from home and your In-Tank Fuel Pump packs up (this will be the second time its happened in 2 years) and cannot be fixed at the side of the road like an external pump can

That would be a very expensive recovery and the chances of an external rubber Fuel Pipe failure must be close to zero

 

100% correct OB. More chance of pigs flying! I believe the real reasons for intank pumps are cheapness of manufacture, fewer parts, simplification etc etc. No question external pumps are far easier to deal with once the guarantee runs out!

 

FYI and comparison, naturally aspiring Corvette needs about 50 gph to produce 600 ponies. This would be 190 liters per hour.

 

Hi Greg

There is no comparison, the external fuel pump is by far and away a much more substantial piece of kit and if it failed then someone I know who's in the kit car business, could bring me one out and I could have her back on the road in an hour!

Which is how long it took me the first time I had to renew one, even though I had never done it before