Hey all, After filling up the tank a couple of days ago, I've heard a knock, knock, knock sound from the engine for the first time. Could this be related to the gasoline? Thanks for any help, Wyld 1972 Mercury Comet GT
If you hear the knocking when the engine is pulling it could be too low of octane. If you hear it all the time it could be something mechanical like: A loose Main Bearing is a powerful dull thud or knock that take place regularly every other revolution. The knock can be confirmed by disconnecting the plug wire next to this cylinder. The knock would be less audible. Loose Rod Bearing is a metallic knock that can be heard the loudest at about 30 mph. The knock can be reduced or eliminated by disconnecting the plug wire to this cylinder. Loose Flywheel is a thud or click which is usually irregular. To test, idle the engine fast and shut off the ignition. If a thud is heard, the flywheel is loose. Loose Piston Pin is a sharp double knock which is usually heard when idling. Severity of knock should increase when the plug wire is removed to this cylinder.
There used to also be a thing called fuel pump knock in small block fords. Also known as front main bearing knock, caused by too much spark advance at idle and a worn front main bearing. It was heard at 800-1600 rpms under load.
more on engine knocking It's probably more like a pinging sound. Pings faster the faster I drive. The reason I asked about the gasoline is that when I was a wee young child, I vaguely recall one of the gas company's advertisements about using their gas to eliminate engine knocking. Whaddathink? Wyld 1972 Mercury Comet GT
Yep I remember that commercial. Ping ping ping all the way home. Try putting a can of octane booster in it and see if it helps
These diagnostic suggestions would be good on the "Cheap Tricks" thread. http://mmb.maverick.to/showthread.php?t=52814
I used all the octane boosters and never found any that worked. Fill her up with 93 octane Chevron. If that doesn't work, back off the timing a wee bit till it does.
Engine ping (detonation) is like a rattling sound under load. Its actually the shockwave from the flame fronts colliding and breaking the sound barrier. Really high combustion temps and pressures. Can do alot of damage over time.
Put some marbles in a jar, then gently shake. That is what fuel related spark knock or ping sounds like. It occurs when you press the accell pedal while the car is in gear. It doesn't happen at idle, coasting, or revving in park.
Except in the case of my 331, the first time I had it running and took it down the street. Had a tank full of 87 octane fuel. Damned thing sounded exactly like it was crushing gravel in the cylinders.:16suspect Went one block down the street and promptly returned home where I syphoned 15 gallons out & replaced it with 15 gallons of 93 octane fuel. Never fed it with anything else since.
