Why is there a knocking sound from the top of the engine?

dear user,
In some cases, gasoline problems cause the irregular combustion that leads to knocking sounds in an engine. This can occur because of problems with gasoline octane. Gasoline's octane ratings signifies the amount of compression the fuel can handle before spontaneous ignition. When this spontaneous ignition happens instead of the normal ignition, knocking may occur and can cause damage to the engine. The lowest octane gases are typically the least capable of withstanding compression and are more likely to ignite this way.
Sometimes the sound of engine knocking is caused by something other than the typical combustion process problems. For example, some types of mechanical issues may cause these knocking sounds. Such mechanical issues can include defects in the crankshaft bearings, broken flywheels, and water pump bearings that are worn out.

faisal

Older tachometers do go faulty. This sounds like it. You should be able to get an inexpensive replacement unit from a breakers yard.

check for broken exhaust rubber mounts and if so that will be the muffler knocking until the engine smooths out to idle.

Possibility of a vacuum leak somewhere around your engine. That would cause what you are experiencing and cause a check engine light as well.

Good luck.
Semper Fi,
Z

We do no thave this engine in the US so have no info on it.

I have the same car and when she got around 200,000 i had to start running a heavier grade of motor oil. If you have high mileage then the cam support bearings, crankshaft support bearings have excessive oil clearance. Listen to the knock with the hood open. If the sound is a deep low tone knock then it is the lower end of the engine. If the knock is high pitched like a tic tic sound it is usually in the top end. Lower end is where the crankshaft and pistion are located and the top end is where the valves and camshafts are located in that engine. You can take a broom stick and probe around the engine (careful not to touch moving parts) and put it to youe ear with a little presure and you can hear different sections of the engine to see where the knock is the loudest. Kinda like a doctors stefascope. If it is more like a grinding noise it could be a tensioner pulley, idler pulley, alternator bearing, a/c compressor clutch.

3.0L Engine

1. Before servicing the vehicle, refer to the precautions section.
2. Disconnect the negative battery cable.
3. Drain the engine coolant.
4. Remove or disconnect the following:
   Wiper and blade assembly Top cowl seal and panel Window washer hoses, from the ventilator louvers Left and right ventilator louvers Heater air duct Timing belt
5. Mark the left and right camshaft pulleys with a touch of paint.
6. Remove or disconnect the following:
   NOTE Be sure not to mix up the pulleys.
   Right and left camshaft pulleys bolts Pulleys from the engine
   No. 2 idler pulley by removing the bolt 3 clamps and engine wire from the rear timing belt cover 6 No. 3 timing belt cover-to-engine bolts Water pump nuts/bolts Water pump and gasket from the engine
   
   
   Fig. Exploded view of the components to gain access to the water pump-3.0L engine
   
   
   
   Fig. Exploded view of the water pump and related components-3.0L engine
   

To install:

1. Check that the water pump turns smoothly. Also check the air hole for coolant leakage.
2. Apply liquid sealer to the gasket, water pump and engine block.
3. Install or connect the following:
   NOTE After tightening the bolt, be sure the idler pulley moves smoothly.
   NOTE Be sure to align the knock pin hole on the camshaft pulley with the knock pin on the camshaft.
   NOTE Be sure to align the knock pin hole on the camshaft pulley with the knock pin on the camshaft.
   Water pump, using a new gasket. Tighten the nuts/bolts to 53 inch lbs. (6 Nm). Rear timing belt cover. Tighten the 6 bolts to 74 inch lbs. (9 Nm). Engine wire with the 3 clamps to the rear timing belt cover No. 2 idler pulley. Tighten the bolt to 32 ft. lbs. (43 Nm).
   Right-hand camshaft pulley, with the flange side outward.
   Tighten the camshaft bolt to 65 ft. lbs. (88 Nm), using the removal tools Left-hand camshaft pulley, with the flange side inward.
   Tighten the camshaft bolt to 94 ft. lbs. (125 Nm), using the removal tools Timing belt
   
4. Fill the engine coolant.
5. Install or connect the following:
   Heater air duct Left and right ventilator louvers Window washer hoses to the ventilator louvers Top cowl seal and panel Wiper and blade assembly Negative battery cable
6. Start the engine.
7. Top off the engine coolant and check for leaks.

Hope this help.

Variable Valve Timing

sounds like it could possibly be a u joint in your four wheel drive.

Try checking for vaccum leaks, use carb cleaner and spray it around the base of carb, vaccum hoses, edges of intake manifold, take pliers and squeeze the big line to brake power booster & see if it changes, pull the pcv valve out and cover with your finger see if it changes idle.