Ford F150 knocking noise when starting? 11 Causes And Solutions To Fix It!

Ford F150 Rear End Clunk
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If you are a frequent traveler and have been using your Ford F150 for a long time, you would have come across the issue of the Ford F150 knocking noise when starting or idle.

This is one of the irritating experiences one would go through, especially when the F150 runs smooth and nice otherwise under other operating conditions.

The Ford F150 knocking noise when starting is usually the due to several underlying issues including but not limited to piston slap, a sticky tappet, bad cam phasers, inadequate lubrication, worn-out seals and bearings of engine parts, malfunctioning oil filter, a bad timing belt or chain tensioner, use of a low octane rating fuel, faulty spark plug, etc.

No one would want to live with this problem of the engine creating knocking noise. Here in this article, we will discuss all possible root causes in detail.

Are you also facing the issue of Ford F150 knocking noise when starting? Then you are at the right place! Here, you will get all your queries answered. So, stay tuned!

What Is Engine Knocking?

The knocking phenomenon in the case of spark ignition gasoline engines occurs when the uncontrolled combustion of the air-fuel mixture occurs at areas outside the envelope of the ignition flame front initiated by the spark plug inside the combustion chamber.

Due to this, the air-fuel mixture will be burnt unevenly and the flame propagation and expansion will not be smooth which leads to the detonation of the air-fuel mixture outside the flame front propagation path which typically occurs at high temperatures and pressures than the fuel can withstand inside the combustion chamber.

This detonation instead of smooth will be sudden and the explosive ignition of the air-fuel mixture outside the flame front creates a shock wave sound which is typically perceived as if a metal part is being tapped with another metal part and we call this shock sound the knocking noise coming from the engine.

The air-fuel mixture shall burn only with a spark plug through flame growth and propagation at the right time with respect to piston position inside the cylinder. Otherwise, you may hear a knocking noise.

The knocking typically occurs when the maximum pressure inside the cylinder doesn’t get generated at the right time when the piston leaves the TDC (Top dead center).

Ford F150 Knocking When Starting or Idle? Causes and Solutions to Fix It!

People often ignore the knocking noise coming from your Ford F150 vehicle and consider that the problem may go away with time.

It is recommended to look into the problem and fix it at the earliest, otherwise, this issue may lead to costlier repair operations including the replacement of the entire engine or many components.

Ford F150 Knocking Noise When Starting? 11 Causes And Solutions To Fix It!

Initially, when the knocking problem occurs, it will be easily noticeable in low RPM conditions like during starting and idle.

But as we accelerate the car, the knocking noise goes away when revs increased. You may not observe any knocking sound but that doesn’t mean that the knocking issue is gone, since the knocking problem is due to the uneven and uncontrolled combustion of the air-fuel mixture.

You may be simply speeding too fast to listen to it. That’s it! Eventually, you may start noticing knocking noise even in accelerating conditions after some mileage.

Below are the few reasons for the issue of your Ford F150 knocking noise when starting or at idle running conditions and troubleshoot to fix this problem.

Piston slap

There are chances of the piston and cylinder diameter worn-out over some mileage of the vehicle.

The piston instead of maintaining tight fit tolerances with the cylinder wall, you may notice more clearance between the cylinder wall and piston diameters.

This clearance causes the piston to hit and slap the wall of the cylinder which is called a piston slap.

The piston instead of simply moving up and down may move sidewise as well thereby hitting the walls of the cylinder and hence the Ford F150 would start making a knocking noise when idling.

This typically happens in a vehicle that has covered 150000 to 200000 miles. It is advisable to rebuild the piston and cylinder block at the earliest possible to avoid catastrophic damage to the engine.

If the clearance between the piston and cylinder wall is minimal, you may notice that the knocking disappears when the heat build-up in the cylinder and causes expansion of the piston to maintain tight clearance with the cylinder wall.

Usually, if the oil pressure is sufficient, the minimal clearance will get filled and may not result in a piston slap.

The piston slap is not that much disastrous but the effect on the piston skirt and cylinder would be.

So it is essential to rebuild or replace the piston and cylinder which may fix other potential issues in the system.

Sticky tappet

The valve tappets are the ones through which the camshaft operates the inlet and exhaust valves in the valve train.

If you are using low-quality oil, an oil filter, or a failing oil pump, it would lead to sticky valve lifters or tappet that in turn results in knocking noise when idling in a Ford F150.

Have you used a different oil than usually being used in your Ford F150? If yes, it is necessary to refill the engine with earlier oil grade.

This is because a higher viscosity oil would take a longer time to circulate across the oil circuit and inadequate oil at the tappet also may lead to knocking noise in that area.

It is wise to check the condition of the oil which is getting circulated and replace it if found deteriorated.

If the time interval for the lifters to stop making noise increases, then it is wise to replace the tappets to avoid frequent events of knocking noise when starting your Ford F150.

Whenever you are replacing lifters, it is advisable to replace all lifters in one go and do not selectively replace the lifters to completely get rid of the knocking issue.

Bad cam phasers

The cam phaser is the component that controls and adjusts the position of the camshaft position relative to the position of the crankshaft or the piston.

The cam phasers or cam actuators perform this function with the help of a solenoid valve that is controlled by the vehicle ECM by adjusting the oil pressure through a pressurized oil circuit.

The cam phasers shall lock into place during engine running, but if the cam phasers go bad due to wear and tear, they may not lock and start producing a typical rattling or knocking noise when starting your Ford F150.

Hence it is necessary to inspect and replace the cam phasers if found faulty to get rid of the knocking noise.

Inadequate lubrication

The piston-cylinder arrangement needs proper lubrication between dynamic moving components.

Inadequate lubrication of parts leads to wear and tear and creates a knocking noise when starting, due to direct metal to metal contact between piston and cylinder.

This knocking noise is more prevalent in hot conditions during which the lubrication oil becomes thinner and loses its ability to lubricate parts.

Also, the issue may be due to an oil leak through the cylinder gaskets or the oil has gone bad and needs replacement.

The cylinder also may not be receiving adequate oil due to a large pressure drop across the oil filters caused by a clogged oil filter.

In this case, the knocking noise will persist unless the oil and the oil filter are replaced with a fresh ones.

Defective pulley bearing

Many times the knocking noise when starting comes from accessories connected to the engine like the water pump, power steering pump, or idler and belt tension pulley, which is used to maintain belt tension.

These components usually run fine without any failure but still may produce a knocking noise when starting.

Typically, the pulley and its bearing that are connected to the above parts, if it gets worn out creates a friction interface and your Ford F150would end up making a knocking noise at starting or idling, but once the vehicle starts running, the knocking or ticking noise goes away during acceleration.

It would be because once the pulley bearings that are used to run these parts get lubrication oil during running and also once the parts get heated up and expand, it creates a clearance at those regions where it may be creating friction joint during startup.

This clearance ensures that the knocking noise goes away after a while during high-speed operation.

Hence you may keep on hearing a knocking noise when idling unless the failing pulley is replaced after a thorough inspection.

Worn-out Crankshaft and rod bearings

The crankshaft bearing is the one that sustains several millions of crankshaft rotations and wears out and becomes defective as the vehicle grew old.

The worn-out crankshaft bearing increases the sliding fit of the crankshaft with the bearing and puts undue stress on the thrust bearing and makes a knocking noise only at starting.

But once the engine heats up, the crankshaft may expand and fill the clearance at the bearing interface and the knocking noise goes away after a while.

Similar is the case with the rod bearings which when get worn out would produce a knocking noise since the piston would start rattling and slapping against the cylinder walls while reciprocating inside the cylinder in case of worn-out rod bearings.

Once the engine cools off, the crankshaft would be reinstated back to its original condition and you may start hearing knocking noise again.

If the vehicle is parked for a long time, you may notice the knocking noise when starting, since the vehicle cools off while standing.

But if you are starting the vehicle immediately after a long period of running you may not hear a knocking noise.

If you want to confirm that the issue is due to the bearing, you simply drop the oil pan and look for the metal particles in the oil and replace the bearings based on the findings.

Malfunctioning oil filters

Typically, an oil filter has an anti-drain check valve to prevent the reverse flow of the oil from the engine system to ensure that some amount of oil remains inside the system to keep the parts from getting dry during the next start.

But if the check valve goes bad, then it would drain out all oil from the system and gets collected in the oil pan of the engine.

So, next time when you start your Ford F150 before the oil gets pumped to all lubricated parts, it will run dry and makes a typical knocking noise when starting or during the idle running condition.

But once the oil reaches all important parts, eventually the knocking noise fades away and disappears and you would be wondering why the knocking noise comes when starting or at idle but disappears later.

It is recommended to use a high-quality oil filter with an effective anti-drain check valve to prevent the draining of oil across the oil filter when the vehicle is switched off.

Worn-out exhaust manifold seals

There are no. of seals used in the engine of the Ford F150 for ensuring a leak-proof joining interface.  For example, the exhaust manifold has got seals to prevent exhaust gas leakage.

But if seals get worn out over some mileage of the vehicle or if one or more exhaust manifold studs get broken, it starts producing a knocking or ticking noise when starting in Ford F150 while the exhaust gas leaks through the sealing joint.

Once the vehicle starts running, the exhaust manifold gaskets may expand and seal the leak joints and ensures a leak-proof sealing interface except during the start at which the gaskets are somewhat in shrunken condition thereby not offering good sealing joints and making a knocking noise when starting or idling in your Ford F150.

It is recommended to inspect the exhaust manifold seals and replace them with a new one if it has gone bad.

Bad engine timing belt or chain tensioner

The timing belt is the one that connects the crankshaft with the camshaft to coordinate the piston movement with the inlet and exhaust valves operation for ensuring the air-fuel mixture combustion at the right time inside the combustion chamber.

The timing belt shall be exerting specific tension on the pulleys to work effectively and it does this function with the chain tensioner in place.

If the timing belt gets stretched or the chain tensioner goes bad, the belt may come loose and slip and you may get a typical ticking, and clicking noise which you may mistake as a knocking noise when starting and then goes away in your Ford F150.

The belt would maintain the tension during running and you may not hear the knocking noise once you rev up the engine RPM.

You may thoroughly inspect the timing belt and chain tensioner and replace them if found damaged.

Wrong or faulty spark plug

The time at which the air-fuel mixture shall burn shall be precise and pre-requisite for smooth expansion of the flame front and combustion process.

The ideal spark ignition timing is 20-40 degrees before TDC and the maximum cylinder pressure typically occurs just after the piston reaches the TDC.

But if the spark plugs are either faulty or you are using the wrong spark plugs, then it may advance the ignition timing, and this causes improper burning of air-fuel mixture which causes the Ford F150 to make a knocking noise when starting or at idle conditions.

You may need to replace the spark plug with a new one to end the knocking noise. If the bad spark plug is due to carbon build-up on the spark plug, you may try using a good spark plug cleaner.

Also, you need to check the tightening torque of the spark plug to ensure that there is no spark plug back out. If the spark plugs are loosely mounted on the engine, then it would not appropriately divert the electric charge from the plug to the engine and you may end up experiencing a knocking noise.

Low fuel octane rating

The octane rating of the fuel indicates the ability of the fuel to sustain compression without detonation.

A fuel with high octane rating increases the combustion temperature of the fuel thereby reducing the possibility of detonation.

If you are using a high-performance variant of the Ford F150 that would need a high compression ratio of the air-fuel mixture, then it would need high octane-rated fuel.

Any usage of standard fuel with a low octane rating will result in uneven burning of the fuel and eventually lead to a Ford F150 knocking noise when starting or during the idle condition.

You may look into your owner’s manual and confirm the recommended octane rating of fuel for your Ford F150.

For most vehicles, an octane rating of 87 is fine but for a high-performance vehicle, you may need to go for either 91 or 93 octane rating fuel.

You may also add an octane booster to improve the rating of the fuel to avoid knocking.

Final Thoughts

The Ford F150 knocking noise when starting is typically the issue related to the malfunction in the components which are directly or indirectly related to the combustion of the air-fuel mixture or bad piston-cylinder system components and parts responsible for ensuring the smooth functioning of the engine.

We also could not rule out the low octane rating of fuel being used or insufficient lubrication of the powertrain parts.

If you are a DIY kind of guy, with the information discussed so far, you would be able to troubleshoot the issue of the Ford F150 knocking when starting or idle on your own without the need of any professional technicians, just by using the method of elimination by analyzing one component after another as mentioned in this article.

You may try using a mechanics stethoscope to make life easy while troubleshooting the knocking noise issue to pinpoint the exact root cause by placing the stethoscope near the probable issue area.

We have tried to collate all points that one should consider while troubleshooting the knocking issue hope, you will find the cause and fix the problem!

Happy motoring!




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