Hello from sunny SoCal!
I'm a new member to the forum and this is my first Jag. Question; The hose connected to the cross-pipe at the rear of the engine (shown in the photo) sprung a pretty major leak and needs to be replaced. How do I access the lower end?
Any tips would be greatly appreciated!


Doug S
1990 XJ-S Sport

 

hi and welcome

when you say leak , i presume you mean an air leak , as that crossover pipe and connected hose only balance the air at the back of the engine

there is a cabin heater valve right by it, are you sure it isn't that ?

BB

 

Thanks BB.
OK, now I'm worried. That hose is spewing water.

 

oops

the only way i can think that water will come from the balance pipe is the AAV has failed on the left bank water rail , i can't think what the small vac pipe your arrow goes to comes from at the moment,

BB

 

I agree with Brake Buster.

That crossover pipe is for vacuum. It should not have any water in it. If it does then it is most likely that your AAV (Auxiliary Air Valve) has a leak and is letting water into the pipe.

You need to replace the AAV.

Mark

 

Thanks BB and Mark. Looks like I've got some work ahead of me!

 

As a follow up....on my 1990 XJS there is no nipple on the balance tube and therefore no hose connected to it.

I have an engine out at my shop that came from an '86 XJS. It has a hose connected to the balance tube like the one in your picture. I dont recall where to other end of the hose connects. I will take a look when I go out to the shop tonight and let you know.





Mark

 

Great. Thanks Mark!

 

That hose (vacuume) on a 90 XJS would go to the ECU in the trunk.

 

i think i may actually got to the Ignition control module in the front footwell , for marelli systems

BB

 

marelli line comes from rear r/h manifold. Crossover pipe stub feeds back to ECU in boot/trunk.

 

My '90 does not have that hose but my '89 does.

I followed the hose behind the engine where it connects to a steel line. From there is goes along the transmission tunnel and then over the top of the transmission. It disappears from there and I could not see if it continues to the rear of the car.

It is very possible that it goes to the ECU but I cannot confirm that yet. I will look again this week to find out where it terminates.

Mark

 

yup, its for the boot/trunk mounted ecu for the injectors , not as i previously thought the footwell marelli ecu ,

worrying that it has water in it though , as its a vacuum pipe , i wonder if it had fell off the ecu and has dropped into the rear arch well and has sucked up water ??

this pipe terminates into an ecu mounted right by the battery in the trunk/boot of the car , this tells the ecu the engine load and how long to fire the injectors for for correct fuelling, without this pipe the car will run poorly , there is also a ' reservoir ' as Jaguar call it that is mounted in the vac line by the ecu to hold the vacuum to stop any fluttering of the signal ,

if you look behind the right rear wheel you will see two hard pipe terminations going into the trunk space, one is fuel flow, the other is the vac pipe for the ecu.

this is the pipe here from the heritage site http://www.jaguarclassicparts.com/uk...pipe-5-3-litre
BB

 

Thanks for all the info guys!
The small diameter rubber hose coming off the balance tube is definitely split, and water is coming from it when I start the car or fill the radiator.

 

I'm surprised that the engine even runs. There should not be any water in that hose or the balance tube.

I would suggest not running the engine until you find out how water is getting in there. As you probably know, water does not compress. If the engine ingest too much water it can bend connecting rods. That would be bad.

Mark

 

The air filters are dry so I suppose that's a good sign. Regardless, I haven't run the car since discovering the problem.

 

How absolutely certain are you that the hose connected to the ECU is the one producing the water?

There is no "suck" from the ECU end of the pipe, so I cannot see why water would get that far. A split ECU hose has to be fixed to get proper fuelling, and re-fixing the other end to the steel undercar pipe is all but impossible engine in car. If you can cut out the split and use a hose joiner, so much the better.

With free entry of air into the balance pipe, the car should be over-revving at tickover like mad. Is it? If not maybe the water is actually coming from one of two pipes very close to the ECU vac pipe, and/or the water valve. These carry the water to/from the heater and are just below the ECU pipe/crosspipe. Get someone to fill the header tank while with a very powerful light you take a look at the water and exactly where it comes from. I am very hard put to see how water can get into the cross pipe and be pushed/pulled out of it when engine is running, let alone when the radiator is being topped up. I suspect you have not got to the bottom of the water source.

Finally, the ECU pipe may have some water in it, which could be sucked out by the engine. Maybe first of all blow some compressed air though this pipe, having first disconnected the ECU end of it, to be 100% certain it is dry before doing any further tests.

Greg

 

all good advice

see my original reply to the question
there is no other source of coolant back there.......

BB

 

Actually the engine seemed to be running normal...no ticks or over-revving whatsoever (positive sign?). I'm sure it's coming from the hose I described though. It's tough to get a photo of the split as it is pretty close to the firewall.
Can you describe the location of the ECU end? Like I said I'm new to this Jag stuff.
Thanks again for all the help guys!

 

the ECU is in the trunk , open the trunk , locate the battery , and to the right of the battery by the relays and behind the side reinforcement is the ECU , its quite large

the vac pipe enters the trunk under the battery and goes towards the ecu

BB