Spark knock or bad lifter

RonD said:

It is/was pre-detonation, i.e. pinging/knocking

When you start to load an engine by accelerating or going uphill, the cylinders start to heat up, many notice temp gauge going up a bit while going up a long grade, very normal because............cylinders are running hotter.

Octane is a self ignition heat rating for fuel, 87 octane will self ignite at a lower temperature than 89 octane, which will self ignite and a lower temp than 91 octane, and so on.......

So as the cylinder temp rises it can reach a point where 87 octane will self ignite in the cylinder just before spark plug fires, pre-ignition, this can happen before piston reaches TDC so it actually slows the crank down instead of adding to it's spin, the no power thing.
The noise is from two or more ignition points in the one cylinder, the explosive wave fronts meet and make that metallic sound.

Diesel engines make similar noise and for the same reason, diesels don't use spark for ignition, it just uses heat, heat from very high compression, when the air/fuel mix enters the cylinder and is compressed, it reaches it's self ignition point, but there may be two or more ignition points, so explosive wave fronts meet and you hear the "ping".
However diesel engines are built very heavy duty because of the compression needed so the pinging is not "good" but a little won't hurt the engine.

OK back to gasoline, so pre-ignition is from cylinders heating up, and this pinging creates even more heat, so once it starts it will continue until you reduce the load, by backing off the gas or moving RPM to a better torque range, if your engine generates the best torque at 2,700rpms and you are lugging the engine uphill at 2,100rpms then it will heat up more, at 2,700rpm it doesn't have to work as hard so will cool a bit.

Then there are dirty injectors, injectors get dirty, some more than others, if an injector is passing a little less fuel than the others then that cylinder will have a leaner air/fuel mix.
Lean mix runs hotter, and it is also easier to self-ignite, so double whammy.
Run some injector cleaner in the gas tank once a year.

When cylinders get hotter NOx emissions go up, that's why EGR(exhaust gas recirculation) systems were added, adding exhaust to the intake when engine is under load causes a slower burn in the cylinders and this lowers the cylinder temp so less NOx is generated.
And since cylinder temps are lower.................chance of pinging is greatly reduced.
So if you have an EGR system make sure it is working.

Since you got no pinging on 93 octane then you can be sure it was "pinging" you were hearing.
if pinging seemed like just a few cylinders then for sure run that injector cleaner sooner than later.

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RonD said:

All cylinders get hot when under load, too hot would cause all cylinders to ping.

Dirty injector isn't "slow" just doesn't spray fuel as efficiently or if restricted doesn't spray enough fuel.
If tip is dirty then fuel drips out, so alot ends up on the inside of the intake instead of in the cylinder, and this can make fuel mix lean.
And it could also cause low RPM misfire, although that is more likely to be spark plug or wire.

It would be worth while to pull the plugs and look at each as it comes out, if there is a cylinder consistently misfiring you will see it when comparing spark plugs, so keep track of which one comes from which cylinder.

Because the fuel and oxygen in that cylinder is not being burned during the misfire, some of the fuel remains behind and can form carbon coating on piston, head and valves, also spark plugs.
And most of the oxygen is pushed out in to the exhaust manifold, and it is detected by the O2 sensor, O2 sensor reads oxygen levels in exhaust, too little oxygen means computer is adding too much fuel, too much oxygen mean computer is not adding enough fuel.
So when O2 sensor "sees" the misfires unburned oxygen computer increases fuel on that bank of the engine.
Which causes more carbon build up.
When misfire goes away oxygen level in exhaust drops to normal and fuel mix returns to normal.

Carbon build up creates "hot spots" in a cylinder, the coating doesn't cool like bare metal does with coolant flowing behind it.
So when under load and cylinder heats up cylinders with carbon build up are more likely to ping as the hot carbon ignites the fuel before spark plug does.

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RonD said:

The older Ford spark plug wires should read less than 7,000 ohms per foot.

But also check the boots at the spark plugs they crack and cause spark to arc to metal engine reducing spark in the cylinder.
Also if you can look at the engine while running at night, and use a spray bottle with water to spray wires, look for arcing near where they pass valve covers or...?? any metal part.

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