Pinging at high RPM

85 XJ6, 104k
Starts and runs pretty well except I start to hear a little pinging around 3800 and by 4000 it sounds so bad I try not to run it any higher. I haven’t tried messing with the timing. It’s a little better if I run premium gas but who wants to do that!

Sounds like a timing kit problem to me as well. If all of a sudden, I would check if the dizzy has moved - my Series 1 requires 8 degrees BTDC an easy check . If only at high revs expect you will need a dial back timing light to check advance at different RPMs - that’s about weights and springs in my car. I would buy premium until you sort it. Paul

Does it get better when you back of the throttle? Is it independent of temperature? Also when you’re not in gear?

My first vote, if I had one would be, timing too far advanced for the fuel and driver

Second, would be carbonization of the combustion chamber. Chemical means are available to cleanse them. H20 included… Beware of a hydraulic lock in their use.

Third, and last by a lot. The “Italian tune”. good and bad things can happen…



you do not mention whether the pinging relates to engine load - usually there is hardly any pinging without, but a lot with load. Pinging usually is unwanted early combustion caused by heat and pressure. You also might have an overly advanced ignition, though.

Paul’s and Carl’s advice is sound, of course. Check ignition and, if set up correctly, drive the car carefully to remove any carbon deposits mildly - you don’t want them to ignite nor to get parts of them stuck in the valve openings.

Good luck


75 XJ6L 4.2 auto (UK spec)

Hi all, thanks for the replys.

It has been like this since I bought it a little over 2 years ago; I’ve logged over 10k miles in that time.

I tried running it up to 4500 for a couple seconds in park, engine full warm. It sounded fine.

I drive pretty lead-footed (it’s usually floored or cruising) but I generally avoid letting it go above 3500 and I back off any time I hear any pinking.

Not sure when I’m going to have a chance to look at it.

That;'s good, because pinging, at high RPM/high loads, is what will destroy an engine, tout suite. THAT pinging cannot be heard

That’s what I’ve always heard.

Interestingly when I was growing up my parents had a manual 86 Camry. In fact I learned to drive in it in later years. As long as I could remember that car pinged like mad even at low revs any time you had more than about 50% throttle which was often as we lived in hilly upstate New York. That engine was still running like new at 230,000 miles when the rust finally took it.

Again, it’s at high rpm/loads: that detonation cannot be heard (by a human ear) and will rip an engine apart.

Doubt the Camry lived at those conditions!

Exactly why I do not approve of the “Italian tune up”.
More likely than not to damage stuff, big time…


If–IF–an engine has been running w/o serious detonation issues before, the application of an “ITU,” is unlikely to cause detonation damage.

If I suspected an engine had serious carbon buildup, I’d do the Stoddard’s solvent/water treatment first.

Doing that, under no-load, would not cause any destructive detonation.

ITU as a “cure” for a carboned up engine is what I refer to…

Aye, there are safer ways to decarbon. H20 being the oldest. Being aware of “hydraulic” lock…

Hanging on my shop wall is a trinket. A Mason jar with two tubes soldered in the lid… Hook up to a vacuum line… Inject a mix of alcohol and water… OK idea but flawed… My "fix’ never worked out…


If lightly carboned-up, it works.

That’s interesting, Martin,

around the same time I drove a pre-cat carbed Fiat that pinged at low revs - and low meaning less than 2000 RPM. So I always had to drive around town in second which was terribly loud and fuel consuming. I suppose that was due to an extremely lean mixture necessary to comply with emission regulation without the use of catalyst converters, O2 sensors and fuel injection.

OTOH, the same 1.1 litre 55 hp engine would propel the car to well over 180 kph on downhill autobahn stretches and the +6500 RPM wouldn’t hurt the little engine. Quite to the contrary after some months of low geared winter driving this Italian car definitely needed such an ITU. This procedure burned off oil and soot from the spark plugs and some fresh carbon build-up on the pistons. With excessive carbon build-up this is highly dangerous. As Carl already pointed out rightly: many XK engines fell victim to carbon build-up igniting and burning holes in pistons, mostly on the 2.8 litre engines though.



75 XJ6L 4.2 auto (UK spec)

Sounds like a sensor problem giving the ECU wrong information making it lean out.

On returning from England mine started pinging. Maybe the distributor stuck or moved a little. It could also be lean due to some air leak, but that would be pronounced at idle, or it could be the head overheating because the cooling system is malfunctioning. I’d turn the distributor ccw by a few degrees and if it goes away, be happy.
A sensor problem would show up load related as far as my interpretation goes.

After England, pinging at over 130kph, the spark plugs had lost their sharp edges (but they have several thousand miles on them) but the rest was unchanged. Now with a bit less timing it doesn’t knock or ping but it got a little slower (I think), so might go back up incrementally. Some noise was at low rpm, low throttle after I altered my valve timing, but that is useless information. It runs fine now.

My understanding is that it was the 2.8s that were lightly driven that holed pistons. Those driven with spirit were much less likely to be damaged. Paul

Backing off ignition timing is invariably the first step, Martin!

This should get rid of the pinking, which, as others have said, is definitely destructive - while you ponder further actions. If pinking persists after backing off timing; there might be other issues to address.

The ‘backing off’ process is quick and simple; mark the position of the dist with dots of paint (or whatever|) on the dist and block. Then loosen the dist clamp and turn the dist clockwise (say 1/8"), reclamp and test drive…

You should of course check the actual ignition timing - to establish a benchmark. Ign timing is regulated by centrifugal advance, increasing advance with rpms and varied by vacuum input. Disconnecting the dist vacuum hose and test driving is another simple viable test - which may indicate something…

It is also relevant to check vacuum at the dist with the engine idling. If you read manifold vacuum; you have the ‘European’ set - and initial advance must be set accordingly…

As others have said; pinking usually relates to engine load - but rpms is not immaterial…

xj6 85 Sov Europe (UK/NZ)

True, Paul - the 2.8 litre cars constantly driven by test drivers never had a chance to build up carbon and hence showed no problems.

Cars driven by low-intensity users in short distance service and city traffic had a chance to build up considerable amounts of carbon that ignited and burned said holes into the pistons. I suppose that even drivers as described above occasionally took their cars on the motorway. The short-geared and higher revving 2.8 l engines then became much hotter than usual and eventually the carbon residues ignited.



75 XJ6L 4.2 auto (UK spec)