Factual error: When the evangelist first enters the mansion, Mrs. Peacock calls him a beatnik. However, the movie is set in 1954, and the word "beatnik" was not coined until 1958. (01:15:25)
Factual error: In the culminating scene where Fletch is held at gun point and escapes by turning on the gas valve in the fireplace and then igniting the vapors into a ball of flame, he actually turns the valve into the off position (valve is perpendicular to the pipe). (01:32:00)
Suggested correction: The valve was in closed position (perpendicular). He opened the valve (turned parallel to pipe).
Factual error: There's a couple of scenes where Izzy goes into a speech about how he came to America when he was 10, and he owes so much to that country. The historical Izzy Einstein came to America when he was 15.
Factual error: During the big final battle of the movie the bad guys throw around Molotov cocktails, bottles with a rag stuffed into the top of it filled with gasoline. Problem is that the cocktails explode and shatter glass, when in reality Molotov cocktails don't explode they simply smash. And on top of this the first few cocktails that were thrown at parked cars weren't even on fire, rendering them useless.
Factual error: After the car chase in the film, as the car leaves a mess of vehicles behind it, it is obvious that the directional flow of the "props" traffic was on the left side of the highway, as if the film was shot in England. But it was shot in USA. The direction signs on this Los Angeles highway are also not visible to the traffic. Drivers would have to look back to see what exit they just missed.
Factual error: Near the end, Angelo Partanna gets off an A Train at 18th Avenue to meet Charley. The A Train has never stopped at 18th Avenue. (01:50:00)
Factual error: The fence surrounding the HARP facility that Remo and Conn break into is supposedly electrified. Not possible - it is a standard chain link fence affixed directly to aluminum posts driven into the ground. If it were electrified it would have to be insulated from the posts; the way it is shown in the film, the electricity would shunt into the ground. When the front-end loader hits it, a plume of firework-like sparks erupts from the point of impact. Also not possible - there was nothing in the bucket of the loader to detonate and the metal hitting against the electrified fence would, at most, cause some small electrical arcs.
Factual error: The supercharged "Honda 750" motorcycle is actually a Honda Rebel 250.
Factual error: Peter Coyote describes the killer as "not a psychopath. He's an ice man," implying the killer is too calculating and manipulative to be considered a psychopath. This is a common misconception: a cool and calculating manipulator is exactly the standard profile for a psychopath. Most people who make this mistake are usually conflating psychopathy with psychosis (or being "psychotic"), when those are actually two separate and quite different conditions.