1987 Olds backfire problem

August 14, 2011 10:32 AM

1987 Olds backfire problem

I have an 1987 Olds Cutlass Calais with a 2500cc four-cylinder and throttle-body injection.

I'm experiencing backfire at about half-throttle starting off from a full stop. This happens on a fully warmed up engine and the backfire is much worse on a hot day.

I'm stumped. Any ideas?

posted by millerizer to Travel & Transportation (6 answers total)

Have you changed the spark plugs? An intermittent spark could introduce uncombusted vapors into the hot exhaust system.
posted by kuujjuarapik at 11:02 AM on August 14, 2011

Response by poster: Thanks for your response. It is very logical.

Unfortunately, it is not the spark plugs; they are good.
posted by millerizer at 11:08 AM on August 14, 2011

Get the rest of the tuneup. A backfire is mixed air and fuel exploding when they are not supposed to. If that engine has a points-and-rotor ignition system, the points could be shot, the rotor could be damaged, or the distributor could be arcing between towers.
posted by Kirth Gerson at 11:55 AM on August 14, 2011

Best answer: Sounds like you've got an early Iron Duke Tech IV. Could be a bad MAP sensor (or MAP vacuum hose), a leaky injector, a bad fuel pressure regulator, bad oxygen sensor, or a vacuum leak, too. Anything that supplies fuel fumes to the engine at the wrong time, or that changes the air/fuel mixture markedly at part throttle is suspect. I'd check the MAP sensor first, and then the injector, if the engine has more than 60,000 miles; both of those parts fail early.
posted by paulsc at 12:57 PM on August 14, 2011

Check the distributor cap, those had a habit of melting on that engine. What happens is that the heat from the exhaust manifold warps the cap and makes the ignition timing incorrect, resulting in those symptoms.
posted by gjc at 9:29 PM on August 14, 2011

Response by poster: You said check the MAP sensor first and you were absolutely right--problem solved. Thanks a lot!
posted by millerizer at 8:16 AM on August 30, 2011