Toyota Repair: 4RUNNER Missfire, fuel pressure regulator, change spark plug

Question
Hi Ted
Can you please help me i have one 4Runner 5VZ-FE engine i have tryed everything measured all the plug wires change spark plug measured Airflow sensor but when i blok off the return fuel hose the engine runs fine.
Do you have any idea what can be wrong
Brgds
Thomas Erichsen

Answer
When you are blocking the return hose you are increasing the fuel pressure because you are preventing the return of any fuel back into the tank, the most common cause for this is low fuel pressure from the fuel pump or a bad fuel pressure regulator or a leak in the system somewhere which should be obvious because of a strong fuel odor. It could also be caused by a clogged fuel filter. By any chance is the check engine light ON?