[HELP] 2003 Venture, Engine knocking, 420, 304, 742

[HELP] 2003 Venture, Engine knocking, 420, 304, 742
sorry, i am very new into car, and my family is a bit strip on funds right now...

my family car now has problem, it has engine knocking sound and the above 3 error code: 420/304/742

does anyone know whats wrong and how do i fix it?

Those are not standard error codes....

If engine is knocking, is coolant/ oil levels full? Does oil look milky?

i refill the coolant, and all the oil are full, they dont look milky tho, i jsut had an oil change a month ago

So the coolant was low, I bet you have some bad intake gaskets and the thing could be eating the coolant, may have washed out the rod bearings, if so then the lower end is trash and you may be engine shopping.

so the worst it i need to buy a new enginer...that will be expensive right? and waht is the best scenario? as you said about the washed out rod bearing, does it happen if u keep driving under the same condiction? b/c ever since i hear the knocking, i havn't drive it.... it has been in the parking lot, and i am thinking bring to mechs 2morrow morning...

If damage isnt too bad, then maybe a new set of bearings/ etc, but dont hold your breath, new engine would be expensive. How bad is the knock? If it is real loud probably a rod knock, does it knock reguardless of RPM- rod knock. If it only knocks at a certian point it could be a collapsed lifter or belt tensioner etc.

only knocks when i press the gas, do u have suggestion how i transport it to mechs b4 do more damage? do i drive slowly? it is about 20 min @ 30km/h

Does it sound like it is comming from under the truck or from above? I would use a tow strap and pull it (not running) to the mechanic (thats me tho.) Can you drive it easy and not have it knock?

if i dont press gass pedle...lol...i think it sounds from the front...???? lol i am no idea about cars

Code 304 is misfire cylinder # 4. Is your MIL flashing? It should during misfires. Cylinder #4 is the middle one at the front. Pull the plug and have a look at it.

P0420 is Catalyst System efficiency below threashold.

P0742 Is torque converter clutch brake switch circuit high.