Hi all, just looking to pick your brains on a mystery bypass pipe that I have located on my newly purchased 1983 XJS 5.3 litre.

I blew a heater hose recently and while replacing it found a no longer connected metal bypass hose that runs From the air pump (emission control pump) under the RH exhaust manifold to the back of the motor and up to the centre of the valley directly beneath the heater tap.

it looks like a bypass hose similar to that which is fitted from the water pump on some 6 cylinder models and follows a similar route.

There is nowhere obvious for it to connect at either end. Both ends have old rubber hose fittings still attached, the forward end has a large rubber hose fitting which looks very much like the 6 cylinder water pump to bypass fitting! The pipe is rusted out so was likely once a coolant bypass.

Does anyone have any ideas on what this was / is? I’m thinking either part of the emission control system or a coolant bypass from another model that has somehow found its way into my car?

My 1979 XJS does not have the same bypass and none of the photos I’ve viewed of V12 Engines, in and out of cars, show a similar bypass!

Out to those with more knowledge than me!

 

Offhand it sounds like your air injection manifolds have been removed.

This pic may help. It shows the plumbing of the system....although only one of the air injection manifolds is shown.

Item #13 is the pipe from the air pump to the check valve at the rear of the engine.

https://parts.jaguarlandroverclassic.../brand/jaguar/

Cheers
DD

 

That’s the one! I guess somewhere along the way someone decided it was no longer required.....for now it’s not as we don’t have any emissions testing but maybe one day I’ll get it sorted!

Thanks for your very quick reply, it really is greatly appreciated!👍

 

To a degree, the system was intact on my 1990 XJS... After reading here, happily, one of the first things I did was remove everything to do with it, except the metal tubing you mentioned (the metal sections I hear are hard to remove completely)... If you look closely, you will probably see where all of the inlets in the area of the intake manifold on top of the engine were blanked off and filled with bolts (or something) to block/cap them. If you imagine the added tubing and piping in an already very crowded intake system, distributor, fuel injection, cruise control, AC, S plugs, coils etc etc etc you my understand why so so many owners just did away with it all. I removed the appliance even, that was driven by an extra belt up front. PITA

All I'm saying is - maybe don't make a place for it on your to do list... It's my opinion,,, I get that,,, but it's just not worth it. Not needed and for me,,,, my list was so long going in I'm glad I was advised not to waste headspace trying to figure that system out. Just my suggestion...