The car was running fine until last night when the car started to lose power while driving about 100mph on the freeway. I was close to my exit so I exited and drove home very slowly. Since it lost power on the freeway it's been making noise and it lacks power (I think it might not be firing on both banks of cylinders but I'm not sure) and I smell gas.

Here's a video so you can hear the sound it's making: https://www.youtube.com/watch?v=uW2A...ature=youtu.be

Any ideas?

 

Begin by inspecting the distributor cap and rotor for Marelli meltdown.

Cheers
DD

 

put new caps and rotors in less than a year ago (as well as plugs and wires) but I will check those. . What are other possible causes of this? Could it be a major engine problem? really worried

 

I hate to be the bearer of bad news, but type in "jaguar V12 dropped valve seat" on YouTube, and compare. The Marelli meltdown makes no noise really, just loses power. I haven't torn my engine down, but feel sure it has dropped a valve seat, and that is exactly what it sounds like. Do a compression test next. My E type had a craked valve seat, that "cocked" in the valve seat pocket, and it too, sounded like that. The thing is, most of the time, a Jaguar V12 will not make noise unless something is pretty bad wrong. Due to the design of the overhead cam, the valve nosie will get less with wear. If anything, after 70-100K miles, we all should adjust our valves, as the wear causes the valve to stay closer to the head, which creates more heat, which in turn can cause the likelyhood of a dropped valve seat.

 

Sounds like a dropped valve seat to me. It sucks to advise you so. Does it run hot; ever overheated? I agree with Supercharged. I'd do a compression test ASAP. Valve clearance checks w/appropriate adjustment should be a maintenance item at least once a year now that these engines are getting older.

 

It wasn't running hot. The temperature stayed below the letter N.

Would a dropped valve seat cause the car to lose half the power though? Wouldn't that only affect a single cylinder?

 

Which unfortunately doesn't guarantee against dropping a valve seat as coolant *flow* to all areas is every bit as important as coolant temperature. An air pocket or blocked coolant passage could leave parts of the head without any cooling at all....and you'd never see it on the temp gauge



I agree, unless you dropped several valve seats.

Cheers
DD

 

I'm thinking one "may" have caused the other. The loss of power came first. Excessive heat caused the next. On my car, as it last Saturday, I drove it to a meet, came home. No overheating, no running hot, no loss of power. Yet when I went out and started it later, that very same sound was coming from under the hood. I am very very disheartened over it. As I say, it is the exact sound my E Type made. However, on my E, I couldn't fault the engine, as I was pretty bad about doing 7K rpm pulls very often, just to hear that V12. It was a blast! Either way, I'm looking at pulling this engine apart asap. From what I have read, understand, you DO NOT WANT to be running this engine any more. If the valve seat breaks into pieces, it can at a minimum scar that cylinder, ruin the sleeve.

 

Maybe it's not quite time to abandon all hope. Could it be an exhaust manifold leak?

Try this, which is cheap and easy. Get out your shop vac, or borrow/buy one, and hook the exhaust side of the vac to your tail pipe. Seal it with duct tape or something similar. Turn it on, then go listen under the bonnet on the side of the car you have the vac blowing into. If you have an exhaust leak you should hear the air blowing out of the leak. If all is quite, try the other side.

If it is an exhaust leak, you won't have any fun replacing the gaskets, but it's a much better situation than dropped valve seats.

Note that this wouldn't explain a massive power loss either, but it's something to try.

Good luck with it.

John
1987 XJ-S V12
64,000 miles

 

I agree wholeheartedly with the look for the easiest! And the idea of replacing the exhaust gaskets. I did this too, and it is a major job. I wondered if it had been easier to just pull the engine, lol!

I've not ever heard of the vacuum trick though. Seems for that to work, you would have to take the valve covers off, and loosen all of the cam bearings, allowing all of the valves to shut.

 

Good news One of the ignition coils melted. The sound is from the sparking melted coil.

 

Whew!


Cheers
DD