Random Misfiring


#1

My '99 Olds Intrigue was running rough & short on power. Autozone read a trouble code “random misfiring” (PM3000 I think it was). As suggested, I changed the plugs/wires and checked resistance on all three coils with no luck. Here’s the real spooky thing: while driving down the street a couple days ago, the pipe between the catalytic converter & muffler separated, scaring me and sending all the children getting off the school bus scrambling for cover. There was no noise or odor prior to the ‘drop out’ - is there any chance that the one problems (a catalytic malfunction, or small leak in the area for instance) could be related to the misfiring? A mechanic - before the pipe plummeted - had suggested it might be an injector problem or the intake manifold ($$$) but I figured that an injector problem would trigger a code. Anyway, your topic today about donating one’s car seems appropriate since I have to decide if this car is worth any more of my limited income or not.
Thanks in advance…I’m a true believer in the Tappets


#2

It was probably a P0300, Random/Multiple Cylinder Misfire Detected. Yes, a failing exhaust can be the cause of this.

If a part of the exhaust was physically crumbling internally and restricting the ability of the engine to push exhaust gas out, it can cause your symptoms.

And if you have a leaky exhaust in an area that causes the upstream oxygen sensor to send a false reading, by allowing exhaust to push out the hole or air to be crawn into the exhaust stream before the sensor, the ECU will not be able to properly meter the fuel and that too can cause misfiring and your symptoms.

Fix what you know’s broke. Then, if the misfiring and low power persist, post back. My money is on a crumbling system having caused a restriction.

PS: the tappet brothers rarely visit here, but there’s a bunch of us denizens willing to help.