pinging

How can I get my car to stop pinging like a bunch of marbles on exceleration. I changed the knock sensor and adjusted the timing to 12 BTDC, new cap, rotor, plugs, wires.. It that a sign of a worn distibuter.

[Clifford Pope]

Could be carbon build-up over a high mileage, or a weak mixture?

[ravennexus]

anymore info on the car.

model
engine
fuel used
etc?

[Casanova]

I have this too.

'91 240 SE Est.

Pinks like bu**ery on hard acceleration. My 'chap' says timing is ok and put some injector cleaner down it - but no better.

If it is coked up, don't they reckon a ring of coke around the bores helps to seal the pistons ?

[Clifford Pope]

They do, but I've never been too convinced about that business of leaving a thin ring round the top of a piston when decoking. Carbon down the side of the piston I can just about accept. But whatever good it does for oil consumption would be more than offset by the potential damage from pinking.

You might like to try my easy decoke method. No guarantees, at your own risk!
Take a jam jar of water about half full, and balance it on top of the inlet manifold. Get a long thin piece of rubber tube, and substitute it for the vaccum inlet to the flame trap. Put your finger over the other end, and start the engine. Rev it a bit, then dip the end MOMENTARILY into the water, so it sucks in a tiny bit of water. Rev the engine to keep it going - it will splutter and hesitate a bit. Then repeat, a bit at a time, until you have used about 1/8" of water.
Rev to clear, then shut down. Leave for a few hours.
On restarting, it may hesitate for a second, but will then blow out a cloud of steam-cleaned carbon. Take the car for a good run, then replace the spark plugs.

It really does work. I have used it in my 93 240 after 300,000 miles, and also on a 63 Triumph 2000. Both had a tendency to pink which nothing else would cure, and both were instantly cured.
It is based on an old and very crude trick of pouring water into the carburettor, which is risky and liable to destroy the engine by hydraulic lock. My method merely ingests a tiny drop of water which is instantly vapourised. It takes very little.
One of the tell-tale signs of a leaking head gasket is an unnaturally clean combustion chamber.

[Casanova]

Thanks for that - sounds like it is a very precise operation. What about putting good old Redex in the plug holes ?

[Clifford Pope]

I tried a variety of methods, including injector cleaner petrol additive, cleaner like Redex in the plug holes as you suggest, also I experimented with using carb cleaner on a plastic bottle brush through the plug hole with the piston on TDC.
Nothing seemed to shift the deposits.
I didn't really believe the steam method would work, and I was very fearful of overdoing it. I lost my nerve after only a few "sips", so was amazed at the difference it made.
It has just occured to me that may be simply spraying water mist from a gardener's spray bottle into the air inlet might work.

[Casanova]

Thanks for that. I am getting really fed up with the noise to which there seems no escape so I will have a go !

[Clifford Pope]

On your head be it! When I tried it I was quite nervous - it felt like a really foolhardy thing to do. But I reflected that persistent pinking is a potential engine destroyer anyway.

Good luck,
Cliff

[martinc]

Dear Love240
I had a 240glt for 12 years and the only time it didnt 'pink' was (i) if it had been on a good run or (ii) if I used Shell petrol.

Run your tank dry and fill full of Shell and see what happens. I got this tip from the Volvo mag years ago.
Cheers