Here are some of the most likely culprits:
* Rod knock: This is a catastrophic failure where a connecting rod bearing has worn out or is failing. This is a very serious issue and requires immediate engine repair or replacement. The banging will typically increase with engine speed.
* Wrist pin failure: Similar to rod knock, but the wrist pin (connecting the piston to the connecting rod) is failing. This also leads to severe engine damage.
* Main bearing failure: The main bearings support the crankshaft. Failure here causes a severe banging noise, especially under load.
* Loose or broken crankshaft: A significantly damaged or broken crankshaft is a very serious problem, requiring complete engine overhaul or replacement.
* Valvetrain issues: While less likely to cause such a *hard* banging, a dropped valve, broken rocker arm, or a severely worn lifter *could* contribute. However, these usually present with a different character of noise than the description suggests.
What to do:
1. Stop driving the vehicle immediately. Continuing to drive will likely cause irreparable damage and potentially lead to a complete engine seizure.
2. Have the vehicle towed to a qualified mechanic. Describe the noise and circumstances in detail to the tow truck driver and the mechanic.
3. Prepare for significant repair costs. The damage is likely serious, and repairs could be very expensive depending on the extent of the problem. You may be facing a rebuild or engine replacement.
Trying to diagnose and fix this yourself is strongly discouraged without significant mechanical experience. The risk of further damage is very high. Get professional help immediately.
