Hey all! I have a head-scratcher (for me at least) for you guys. XJS Marelli, 92. 150k. I have been tinkering with this car for a while now, and have run out of ideas. Things I have done to it: new plugs, wires, cap, rotor, coils, intake manifold gaskets, injector o-rings, valve cover gaskets, fuel pump and filter, smog delete (according to https://foreverjaguar.com/f/smog-blogdelete) and harness rewiring. when I got the car, it idled very high, indicative of a vacuum leak. I replaced the crossover elbows, and the AAV hose, as they were leaking badly. The car then lowered idle a bit ( from 1750 rpm to about 1000) ,which still pointed me in the direction of another vacuum leak. I then deleted the smog according to the above blog, which had me replace the intake manifold gaskets, and while I was in the V, I replaced the plugs, wires, coils, and cap/rotor. Then idled at about 800. Saw some broken insulation on the wires, and decided to redo the harness. so I pulled the injection harness out of the car, and redid each wire, one by one. New wires back in, seems to idle a bit smoother. The main issue I am having is that the car seems to have no power at all. It barely chugs up my driveway at WOT. My trip computer used to work, and tell me the FF codes, but after sitting for about a month (rainy season), the display just shows garbled characters. It used to display an FF13. ANY help would be much appreciated.
OTHER IMPORTANT NOTES: the car has had one side (B bank) of the catalysts tampered with, there is a rectangle where someone has "punched out" the cats on that side. but the other side is intact. it is at the muffy getting two "test pipes" installed.

 

Have you used a spark tester to verify that you actually are getting spark to all cylinders? The low power condition suggests you may have an issue, despite new parts, preventing spark from getting to half the cylinders. Another possibility is plugged catalysts, preventing one bank from making any power.

 

Car was just at the exhaust shop, all catalysts have been removed. no change. Exhaust out of the A bank is hot and strong, B bank is cold and weak. Just to test a theory, I fired it up, and pulled the B bank coil wire off, no change in idle. So B bank is totally dead. All 12 cylinders have spark, and all spark looks even and bright. Just ran a compression test, looks like I have some mechanical work ahead of me.
1 145
2 65
3 120
4 125
5 0
6 132
Looks to me like a blown head around 2,3,and 4, along with a nice dead hole on 5. May as well rebuild both banks, as the engine already has 150K. Any thoughts? Tips for overhaul? Also wondering what components, if any, would be comparable to OEM as far as bearings, valvetrain components, and gaskets. Thanks.

 

Is this car new to you? Or at least relatively new to you? Has it sat for a while? It’s entirely possible you have some stuck valves or rings. Thorsen here had that problem that Marvel Mystery Oil fixed. You may need a new head gasket, but maybe not. What are the compression numbers for the A bank?

https://www.jaguarforums.com/forum/x...-244431/page2/