Too much fuel, rough idle, no throttle resonse

XJ-S
1

I bought barn find 83 xjs 12. Will start, run very rough, with no throttle response. Very rich exhaust fumes, and passing raw fuel. I know of the pressure regulators, but can find no info for setting pressure…If anyone has encountered this, or knows how to fix it, please let me know…Thank you…Jim

2

Have you done any maintenance on the engine? Spark plugs air filter?

3

Jim,
A barn find car can have many things wrong with it including the reason it was stored to a wide range of problems that have been created by it sitting for a time unused.

If you are unfamiliar with Jaguar V12 engines and its many related fuel delivery, ignition, vacuum, emissions, and electrical components I recommend that you download Kirby Palm’s excellent “Experience in a Book” from Jag-Lovers" (it is free) and purchase a copy of the Jaguar XJ-S Repair Operations Manual (about $50 on eBay?). Hopefully you already have a copy of the Owners Handbook as it also has a lot of helpful information (if you don’t have the owners manual these also show up regularly on eBay). These will help you a lot in the long run. I own, drive, and work on two V12 equipped Jaguars and I refer to these documents, and others, on a regular basis when issues come up.

If I were in your situation with a barn find car with possibly many unknown issues I would:

  1. do a compression test of the cylinders to make sure that there weren’t any serious show stopping issues like a dropped valve seat before doing anything else

  2. replace the spark plugs, wires, cap and rotor (and check the vacuum advance to make sure it wasn’t frozen).

  3. Drain the fuel tank of the stale fuel, check for rust or debris in the drained fuel and replace the fuel filter.

  4. Hook up a fuel pressure gauge to the fuel rail return line to see that you have good fuel pressure (about 35 PSI).

Of course that is what I would do just to try to get the engine running properly in my garage. This doesn’t include all the work required to get it safely driveable on the road like flushing and replacing all the fluids, checking and replacing brake pads and rotors as needed and removing and replacing all the engine bay fuel injection lines, hoses and belts.

Good luck.

Paul