1999 Buick Lesabre PO440 and PO300 codes

DOUGANDLAURA

MEMBER
1999 BUICK LESABRE
6 CYL
FWD
AUTOMATIC
115,000 MILES

I have been driving with the 440 code (exaust leak) for several months w/ no problem. Today car started missing when I tried to exelerate and threw a 300 code(random misfire). At the same time started smelling like rotten eggs. Brought it home, shut it off. Had a very hard time getting it to start again, but when it did, white smoke billowing out of tailpipe that smelled reminiscent of burnt plastic. Shut it off again. Later went to start it. Will not start at all now. Maybe my exaust leak caused the mixture in the exaust to clog up my catalytic converter? Have also read online that it could be fuel pressure regulator? Any ideas?

1 Reply

BUDDYCRAIGG

MECHANIC
2,262 POSTS

I can see a chain of events happening.

The exhaust leak, the hot air from the leak finally got bad enough to damage the spark plug wires.

The spark plug wires became damaged enough to ground to the engine so the plug stopped firing.

The plug stopped firing, and that unburnt fuel was sent out the exhaust system and was too much for the catalytic converter to deal with.
(that would have been the egg smell)

now the cat has melted into one solid glob and is clogging the exhaust system and the engine cant start (like sticking a potato up a tail pipe)

you can remove the oxygen sensor to let the exhaust gases escape. And try to start the car again.

Good luck