3 codes help 0300, 0420, and 0420pd

ok my 99 ext cab, 4 cyl, 5 sp, has thrown codes P0300, P0420 and P0420PD. i know the 300 is a misfire, 0420 is bank 1 threshold below efficentcy, i can not detect a misfire and i am getting 27 gpm. i don't know what the P0420PD code is and if it a clogged cat (which i replaced 2 years ago) is there any way to confirm a bad cat other than just replacing it.

Always diagnose and repair the first DTC that is retrieved and then retest to confirm repair. DTC's that are retrieved after the first one, in your case, the P0420, can be caused by the first DTC.

P0300 series DTC's are almost always caused by secondary ignition faults: Spark plugs, spark plug wires, distributor cap, distributor rotor, ignition coil. How many miles since the last tune up with AC Delco parts? The P0300 if not repaired, can and will destroy your converter.

Concentrate on the P0300, if the P0420 shows up after repairing the P0300, then we can help you diagnose it. The P0420pd means it has detected the fault happening more than once, pd=pending.

great advice normally i will fix a problem and let the light clear it self as a way of confirming the fix, but now i will reset the light after the repair thanks

Let us know how it goes and what you find.

ok after 3 days and about 120 miles all seems good no cel and no codes. the problem goes futher back than i stated. several months ago i had a code (don't remember the number) small evac leak. i replaced a canister near the gas tank and it did nothing, i ran it like that until 2 weeks ago at which time i replaced the filler tube (a used 1 that i made sure didn't have any leaks, well the light reset itself and came back on 3 days later. at no time did i reset the codes or recheck them just thought that they were evac leaks, next step was to replace the gas cap which did nothing. i then posted on the forum, after reading the replys i reset the codes and they have not reappeared so i am thinking i was just chasing old codes that i never cleared previously, my thinking was make a repair and let the code clear itself, now i believe as stated earlier, codes need to be manually reset. thanks for the replys

ok it's back after 1 tank of gas about 400 miles, p0420 bank 1 below threshold

Here are the diagnostic steps for P0420:


Page 1 of 3 http://i561.photobucket.com/albums/ss58/cwhook/P0420page1.jpg

Page 2 of 3: http://i561.photobucket.com/albums/ss58/cwhook/P0420page2.jpg

Page 3 of 3: http://i561.photobucket.com/albums/ss58/cwhook/P0420page3.jpg

ok i reset the code on the 27th and it took this long to show up again (just hoping it would disappear) now it is time to chase the code upon looking at the diagnostic steps it states for a 4.3 i have a 4cyl will it make any difference thanks old master

Same holds true with the 2.2L diagnostics are the same.

thanks i will check it out tomorrow