And I'm not talking about trying to go 90 up a hill. Just regular driving.

 

Incorrect base timing (too much initial advance), running too lean, running too hot, excessive carbon build up on pistons......

Checking the timing is the easiest place to start.

Cheers
DD

 

Do you get fuel from the same place ALL THE TIME????????????

If yes, them MAYBE it's NOT 91 (just because the pump label says it is?)

I would try fuel from another brand and see if the problem persists.

bob gauff

 

are you sure its actually knocking? i had the bolt that holds the front pulley on come loose on me and i swore the car was knocking until i realized turning the ac on made it stop and i eventually figured it out.

 

Hi, I have an '88 3.6lt XJ40 and had the same problem. As my car has a high compression engine I found that I have to use 98 octane fuel. This has solved the problem

 

the highest octane I can find in central texas is 93 octane, and thats higher than you will find in most parts of the US(except near racetracks they sell 100 octane) so 98 is a bit higher than most of us have access to
although, on that note try an octane booster and see if that helps

 

Here in Aus the recommendation is that they be run on Premium (96 Octane) fuel. Running them on 91 would void the engine warranty here if the car was still under it. Ask Brutal (Forum Senior) for the answer, but don't keep driving it if pinging (pre-detonation) continues. It will end up buring a hole in your wallet as well as a piston or two.

Cheers,

Languid

 

I filled it up with Shell 91 and it's still doing the same thing. It kind of sounds like the old VW Bugs did. I'm starting to wonder if the exaust is starting to leak??? I'll be calling the Jag service place tomorrow. It only does it when I'm accelerating.

 

When discussing octane, it is always useful to take a look at the poster's region. Different octane rating systems are used in different parts of the world.

 

Very true- North America uses a different rating system from the rest of the world. 91 in Canada and the USA is 95-96 everywhere else.

 

It sounds like it's the exaust manifold. I had it replaced less than a year ago so it better be fixed for free this time.

 

I'm not sure of your exact sound. I can only go by the words "pinging." I have had that tick/tap sound for a year, I thought it was the exhaust manifold gaskets, I replaced them, its a definite lifter, not exhaust. On mine anyway.

 

It was the exaust manifold gasket AGAIN. It had just been replaced in Sept 2011. At least it was free to fix but why would it wear out that fast?

 

Steve,

The only reason I can think of immediately, is that the flange(s) are warped, allowing exhaust gases to slowly escape which will gradually 'eat' away the gasket until it becomes noticable. Putting a straight edge across the flange will tell you. I should think it would be pretty hard to detect otherwise, until the problem reappears.

Cheers,

Languid