What is the situation when the engine experiences intake backfire under load?

[DiJulia]

There are many reasons that can cause intake manifold backfire, which may involve issues with the fuel supply system, ignition system, and other aspects. Engine intake manifold backfire: Refers to a fault phenomenon where the air-fuel mixture combusts within the intake manifold, causing flames to shoot out from the intake port. Fuel system faults: Intake manifold backfire occurs due to insufficient fuel supply, resulting in an excessively lean air-fuel mixture. A lean mixture slows down the combustion speed, causing combustion to continue until the end of the exhaust stroke when the intake valve opens. The fresh air-fuel mixture then encounters unexpelled combustion gases in the cylinder, igniting and flowing backward through the intake manifold, resulting in backfire from the intake port. Ignition system faults: Intake manifold backfire can occur due to delayed ignition or poor spark quality. On one hand, this delays the start of combustion; on the other hand, it also slows down the combustion speed, causing combustion to continue until the intake valve opens, leading to intake manifold backfire. Accompanying symptoms may include: slow engine speed increase during acceleration, noticeable backfire during rapid acceleration, sometimes backfire during gradual acceleration, muffled exhaust sound from the tailpipe, and the engine temperature rising easily. If severe engine vibration, exhaust backfiring, and significant power loss accompany the intake manifold backfire, it is often caused by ignition misfiring. Due to ignition misfiring, when a cylinder is in the intake stroke with the intake valve open and the spark plug fires, intake manifold backfire can occur. If inspection confirms that the high-voltage wires are correctly connected to each cylinder, the issue is likely a distributor cap breakdown. It is important to note that with minor distributor cap breakdown, the engine may operate normally under no-load conditions, but backfire may occur during heavy load climbing when the engine is hot, accompanied by noticeable power loss. If the engine runs normally at idle but occasionally backfires during rapid acceleration or deceleration, exhibits irregular backfire at high speeds, or frequently backfires when driving on uneven roads, for traditional contact-point ignition systems, it is often due to poor distributor grounding. For electronic ignition systems, it may be caused by poor grounding of the ignition module or loose sensors in the ignition system. A poorly grounded distributor or ignition module may generate high voltage when engine vibration causes grounding issues, equivalent to disconnecting the low-voltage circuit. If the distributor rotor happens to point to a cylinder in the intake stroke, it can cause intake manifold backfire.

[SanJameson]

When driving, the engine backfires or detonates under high load, sounding like a popping noise, which is quite alarming. I once encountered a similar issue while towing a trailer uphill, caused by the ignition timing being set too early or the air-fuel mixture being too lean, leading to premature combustion before compression. Carbon buildup on spark plugs or aging ignition coils can also easily trigger this, and the probability of system errors increases under heavy load due to higher intake pressure. When I heard the popping sound, I immediately slowed down and pulled over to avoid engine damage. If you experience a similar situation, I recommend first checking the basic ignition system and air-fuel ratio, avoiding pushing the engine when fully loaded. Safety first—get to a professional shop as soon as possible to read the fault codes and address the issue properly.

[Wilson]

Engine backfire and detonation under load are usually related to improper air-fuel mixture ratio or ignition issues. The specific symptoms include intake manifold popping accompanied by a ticking sound. For a simpler check, start with the spark plugs to see if they are dirty or have excessive gaps affecting ignition stability. Then check if the ignition timing calibration is lagging, as this is more prone to errors during load acceleration. Sensor issues, such as a dirty mass air flow sensor, can mislead the ECU into adjusting the air-fuel ratio too lean, causing high-temperature detonation in the engine. Based on my experience helping neighbors with car repairs, I suggest first cleaning the relevant sensors and replacing aged components. If the issue persists, use a diagnostic tool to check the data stream to prevent long-term neglect from burning out valves or pistons.

[SanAlana]

Intake backfire detonation is more likely to occur when engine load increases. The main cause is premature spontaneous combustion of gases during the compression stroke, such as lean air-fuel mixture or advanced ignition timing. Valve sealing issues causing gas leakage allow flames to flow back into the manifold, producing noticeable noise. Solutions include adjusting timing to ensure accurate ignition, cleaning carbon deposits to maintain proper valve clearance, and ensuring stable electronic control system operation to prevent sensor drift. I recommend prompt repairs to prevent damage to other components. Driving safety is paramount - avoid overloading the vehicle or forcing performance under heavy loads.