Causes of Engine ‘knock’

Preamble
‘Knocking’ or ‘Pinging’ is a typical ‘rat-a-tat-tat’ kind of a metallic noise that a petrol engine lets out due to ‘pre-ignition’, when accelerated on load. Its ‘volume/loudness’ and ‘frequency’, amongst other things, depends upon the loading on the engine and its ‘rpm’. If allowed to persist, continuous knocking over a period of time can burn holes into its pistons and thus kill it completely.

The most common causes of knocking in a Petrol engine - and their preventive remedies - are in the following order:

1. ‘Lugging’ the engine in the wrong gear. i.e. shift one step down.
2. Over ‘Advanced’ Ignition timing - reset to OEM recommendation.
3. Adulterated/Fuel of lower than recommended ‘Octane’ Rating - go up one grade than what you have been using.
4. Fuel-Starvation, either due to a clogged Carb OR Fuel Injectors in an Mpfi Engine - get them cleaned up OR use well-branded Petrol Additives for the purpose.
5. ‘Anti-Knock Sensors’ not working in an Mpfi engine - for whatever reason - requiring professional intervention. Likewise, the Vacuum Advance/Retard feature in the Ignition Distributor being faulty in a Carb type engine.
6. Excessive ‘deposits’ within Cylinders AND Exhaust Line - mostly due to repeated short runs - more so in an Mpfi Engine coz it’s programmed to run in an ‘Auto-Choke’ mode when ‘Cold’.
7. Sticky Brakes. If so, the Car won’t roll freely even on the slightest of inclines when ‘let loose’.
8. A worn-out engine - will require a ‘compression check’ at an authorised Workshop to confirm.

‘In a relatively new car, say, with less than 50 kkm on its Odometer, (8) above will hardly ever apply and consequently, (3) and (6) are the most likely culprits. For the former, one can switch over to the new ‘Premium’ Petrol’s that are now available with an Octane rating of ~ 90 and if that doesn’t help, go for a non-stop 150+ km Highway drive every 3-months at speeds > 80 kph. This is recommended especially for those living in smaller/congested towns and doing short runs as a matter of routine.

By now, the new generation/premium/90-91 Octane petrol’s with additives pre-mixed are available practically all over the country and switching over to them should produce the desired difference. However, when doing so for the first time on a car with, say, more than 10 kkm on its Odo and more so if not having used ‘additives’ earlier on regularly, one should ensure the following:

1. Consume the existing fill upto ‘E’ level.
2. Fill to ‘F’ with the premium 90/91 Octane petrol.
3. ‘Top-up’ again by the time the level is down to 3/4
4. Repeat (3) above atleast twice - before reverting to one’s normal filling-up pattern.

This will ensure that the concentration of gums and glues that the premium petrol will dislodge from the system doesn’t go beyond the in-tank electric fuel pump’s handling capabilities. Otherwise, there’re good chances that they’ll kill the expensive fuel-pump.