03 grand caravan engine running rough and leaking gas out of the valve covers. What is the most common issues. I can smell strong gas smell in van

The alternator is used to charge the battery. There is no reason to believe the replacement has caused the fuel utilization problem, or smoke from the tail pipe, or rough running engine. A good mechanic should be able to examine your engine and find the problem. White smoke could be valves or piston rings worn out. There are many things that cause rough running engine. Fuel mixture controls, fuel leak, faulty timing, there is a long list. Good luck.

Remove the Engine Air Filter Housing and look under it for a vacuum line that goes back to the gas tank You will get a gas smell at times because this is an open line to the gas tank and evaporation container. It's common for the rubber elbow there to split and cause issues. Check ALL vacuum lines. The increase in air into the fuel system is causing a backfire "popping sound" and a loss of power.

this is what we call "dieseling"
it is the engine running WITHOUT spark plugs

This happens when you have leaking injectors and carbon build up in the engine (pistons/valves)

try shutting off the engine while in park
keep your foot on the brake because you might find the engine has enough power to actually move the van

keep us posted

p0455 Evaporative Emission Control System Leak Detected (gross leak).
Check around the fuel tank and by the vacuum cannister. you may be able to smell the fuel.
You will have to go to the underneath van to find the cracked/unplugged hose.

sometimes it could just be your gas cap not tight enough but probably not.

This is commonly caused by a dirty throttle valve and idle speed control valve, have them cleaned.

1. Could be changing the fuel filter
2. Leaking injector
3. The gas cap (tank gas input) is clogged - Gas tank does need some air
4. Pressure check you gas line - should be in the 20s and hold steady for hours. Could be slow leak

There is most likely an engine oil leak that is leaking on the exhast that runs accross the bottom of most toyota engines. Valve cover is common

Sounds like you may need to inspect and replace your fuel line from front to rear. no other reason for your problem.

You more than probably have a gas leak somewhere in the fuel system. If you can smell gasoline, it is leaking somewhere. The lines run along the frame to the engine. The leak might be hard to see or hidden (on top of the fuel tank).

The leak is robbing fuel pressure from the engine, causing it to idle rough, so is probably on the pressure side of the system.

(Most fuel systems, except for "returnless" systems with Pulse width modulated fuel pumps (not very common), have a pressure line and a return line to the tank.