2000 mustang gt engine issues

So you bought it running like this? The guy told you the engine was blown?

It's a 2000 but has a 2003 engine. This suggests to me the previous owner blew the original engine too and replaced it with a junkyard find. If this one has been hurt too I suspect the previous owner didn't leave the car "stock". He probably ran a healthy shot of nitrous in it and hurt both engines, returning it to stock "stock" before selling. Did you scour the car looking for evidence of stuff like mounting bracket holes in the trunk? A hole & grommet to get a nitrous line through? Wiring modifications near the TPS etc?

It sounds to me like it's got at least one dead cylinder and a reciprocating assembly problem (the knock.) There are a couple of kinds of "knock":

- mechanical knock (bearing or piston clearance far too large)

and

- pre-ignition (mixture ignites too early) or detonation (explosion of end-gases in the combustion chamber). These are sometimes confused and lumped into a single term known as "spark knock."

Detonation usually occurs under heavy load when using lousy gas and/or a tune with too much timing. Pre-ignition occurs when hot metal or carbon particles ignite the mixture way before the plug is supposed to.

But it sounds like the knock you have is the mechanical variety.

Pull the plugs. Do a compression test on it. Keep in mind that if it's got a mechanical knock it's probably not worth doing even that since it's likely terminal... It might give you an idea as to which cylinder(s) might be involved.

Look like a full build is in your near future. Gotta love the build threads, everybody gets to spend someone elses money