My 1998 blazer is jerking on acceleration and I received a PO 300 and a PO 420 code. Do you think it is the lower O2 sensor? 158,000 miles and it is original. I have replaced the Converter a few years back and all the plugs and wires changed last year.
Country: United StatesMake: GMModel: BlaerYear: 1998Engine: 6 cyl
hello and welcome to J/A my name is XXXXX XXX I will be assisting you today, please remember I am not their so be very detailed. how may I help you?
what codes are you getting again
po300 and po420 are coming up with nothing
PO 300 and PO 420
i had the converter changed a few years back. Wires and plugs changed last year.
are these codes from a scanner
what kind of scanner
let me check it
actron pocketscan plus
300 is a random multipule missfire
po420 is cat threshold below minimum effeicency The problem could be a bad cat, o2 sensor (Pre- and/or post cat)or o2 sensor wires, or an air fuel mixture problem that has caused the cat to fail. Many other engine operating system failures can cause the converter to not work properly.
if you replaced the cat last year it is probably the down stream 02 sensor the one to the rear of the cat
As I looked at the post o2 sensor it is rusted on there and the wire covering I can easily pull back and see the 3-4 wires that enter the top of the sensor.
the cat was replaced a few years back
if it is a 4 wire it is a heated o2 sensor if you choose to change it your self you can get a o2 sensor socket which is recomended to change it out specially seen it is rusted
ok will do. Just so I know is that a common cause of the jerking on acceleration and those codes? Looks like easy fix if I can get it removed.
well the cat code can be caused by the missfire
the miss fire could be a wet, cracked, damp, worn out distributor cap and rotor bug, it could also be a bad distributor which a worn bushing in the distributor is common in the 4.3 i would start by pulling the dist cap. checking the cap and rotor, and if they appear good check and make sure the distributors rotor bug mount doesnt have excessive play where you can move it around
that is where I would start to be hones
ok sounds good. I know I had that cap replaced before. So will do that and if that looks good will move to the sensor then?
would get ride of the miss first and formost
if its missing it is dumping raw fuel in the exhaust which will give you the 420 code
ok. so the miss fire wouldn't be caused by the sensor then
no the miss fire is the cause of the sensor code sorry if i confused you
should say it is most likely the cause of the sensor code
ok....so the 420 code - start with distributor the 300 code sensor I have 2 seperate issues to fix?
no the 300 code is random multipule missfire which means you have more then one cyl missfireing
ok....so I need to get the miss fire fixed...and the miss fire is caused by something else other then a bad O2 sensor. So start at the distributor to diagnose that?
yes fix the miss fire and it should fix the o2 sensor code
25 is manifold temp sensor
gotcha....wil go after the distributor tomorrow and see what I can find.
Thanks...gave me a place to start. Not the best at repairs myself but at least I have a idea.
Michigan state certified technician with 18 years exp.