My son bought a 83 xjs 12 cylinder it runs but just barely. if you flutter the pedal the rpms will increase. going up a hill you have to flutter the pedal to get it to pick up speed. it backfires until it's warmed up, and even then it does occasionally. we put a new distributor cap on it, but were unable to get the rotor out. is there a trick to it? any help would be appreciated. any pics and/or descriptions would be helpful, we know nothing about a 12 cylinder engine. if we cant get it to Run waht can i switch it out to ?? chevy or ford ?

things we have done replaced the fule filter
Distrubiter cap check plugs

 

That's a pretty old XJS you have there. Despite this the car is fairly easily fixed once one has found out what is going wrong !

Your symptoms look like fuelling to me. The EFI system is Lucas-Bosch D-Jetronic and is analogue with discrete electronic components and not an integrated circuit in sight, and hence no fault codes to guide you, it is all down to basic knowledge. I suggest you have a read of the article below by an expert.

http://www.jagweb.com/aj6eng/djetronic.php

 

A fuel pressure test might be in your future....a hassle on these cars as you have to cut open (and then replace) a fuel line to do it. Not a huge deal, really, but a nuisance.

First, though, I'd check the throttle position sensor. If you have a voltmeter I can post the details....it's pretty easy to do.

Make sure the vacuum hose to the ECU is intact. It starts at the balance tube at the rear of the engine (there's a nipple for the hose) and goes alllll the way back to the ECU in the trunk.

The mechanical and vacuum advance systems for the distributor are known to give up as the decades go by. This is worth checking as yours probably need repair although I don't think they're the root cause of the specific problem at hand.



Don't yank it upwards with much force. You can damage the mechanism under the distributor plate. Take a sharp chisel and cut it off. A couple well placed smacks will usually do the trick....not nuch force is needed.



There's quite a learning curve :-). Making one run properly is nothing you can rush through. And you may well have a stack-up of various faults that are all contributing to the problem. You'll just have to go thru all the sub-systems one-by-one.



Chevy is the most popular by far but you can probably get this one running with a lot less expense and labor than an engine swap.

Post back if you need details on anything mentioned above.

Cheers
DD

 

I had another look at the AJ6 Engineering site I mentioned on my last post. As an '83 your car would seem to have a later Lucas EFI system, similar in many respects to D-Jetronic, but with updated electronics, being a halfway house between analogue and full digital.

Here is an article on this later system: -

http://www.jagweb.com/aj6eng/lucas_efi.php

This site also has a long article on the V12 and its development history by a man who was there at the heart of it.

It is probably also worth checking to make sure all the injectors are firing - they make an audible click, but better to use the screwdriver stethoscope trick on each one, to make sure, because they fire together in groups, (of four, I think).

Also do all the other checks Doug has outlined. Note the vacuum hose to the ECU which is in the boot, a very long pipe indeed !

I hope you can get the car operational and keep the V12 engine, it is a magnificent piece of engineering, part of motoring history, and reliable once you have put right the neglect of previous owners.