p0300 and p0420 codes help!!!

mxpimp2000 · 04-08-2009, 12:58 AM

I just bought a 1998 s10 blaze 4WD automatic with 174,xxx miles on it. it has a missfire problem when i first take off in the mournings or for the first drive of the day. also it does it when im just crusing along at a constant rate of speed but say im goin 70mph on interstate on cruise control it will miss and sputter bad but if im goin 55-60 it wont do it as bad. sometimes it will stop and sometimes it will not. usually after i drive it a while it wont do it when i take off from stops it will only do it at cruise speeds.

i have replaced the distributor cap and nothing. also i had a friend tell me to try to unplug the map sensor so i waited til the next mourning and made sure it was missin so i unplugged it and BOOM no sputtering or missfiring. BUT i bought a new sensor and thought i had it figured out but NOTHING still does the same sh** as before. only if the map is unplugged it wont do it

and i had the engine light checked and it was a p0300 and a p0420 i checked my cat converter and it has an aftermarket one on it so someone has changed it before me

forgot to mention that if u accellerate to pass someone it dosent miss or sputter at all. also after driving for a while it wont do it when i take off from stops just when im at constate speed over 55mph. sometimes it will quit and not do it all day. 90% of the time it wont clear out at cruise speeds just maily clears up from dead stops

what should i try next?

distributor
plugs/wires
coil pack
rotor button
o2 sensor
cat converter
fuel filter

or what?

PLEASE HELP thanks

blindbatts · 04-08-2009, 04:25 PM

random misfires are most likely caused by a vacuum leak.

schveb · 05-23-2009, 01:45 PM

Did you ever figure out your problem? I'm having the same symptoms with my 4.3l> I have changed distributor, wires, plugs, and cleaned my mass air flow sensor with no help. I haven't gotten a p0420 code yet but my cat rattles like the honeycomb is broken everytime i hit or let off the gas.

Let me know what you found out!

Thanks

2separate · 05-24-2009, 08:38 PM

It means, it's time to wave goodbye to your GM product.

04-08-2009, 12:58 AM	#1
mxpimp2000 Registered User Join Date: Mar 2006 Posts: 16 Location: kentucky User is: OffLine	p0300 and p0420 codes help!!! I just bought a 1998 s10 blaze 4WD automatic with 174,xxx miles on it. it has a missfire problem when i first take off in the mournings or for the first drive of the day. also it does it when im just crusing along at a constant rate of speed but say im goin 70mph on interstate on cruise control it will miss and sputter bad but if im goin 55-60 it wont do it as bad. sometimes it will stop and sometimes it will not. usually after i drive it a while it wont do it when i take off from stops it will only do it at cruise speeds. i have replaced the distributor cap and nothing. also i had a friend tell me to try to unplug the map sensor so i waited til the next mourning and made sure it was missin so i unplugged it and BOOM no sputtering or missfiring. BUT i bought a new sensor and thought i had it figured out but NOTHING still does the same sh** as before. only if the map is unplugged it wont do it and i had the engine light checked and it was a p0300 and a p0420 i checked my cat converter and it has an aftermarket one on it so someone has changed it before me forgot to mention that if u accellerate to pass someone it dosent miss or sputter at all. also after driving for a while it wont do it when i take off from stops just when im at constate speed over 55mph. sometimes it will quit and not do it all day. 90% of the time it wont clear out at cruise speeds just maily clears up from dead stops what should i try next? distributor plugs/wires coil pack rotor button o2 sensor cat converter fuel filter or what? PLEASE HELP thanks
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04-08-2009, 04:25 PM	#2
blindbatts Registered User Age: 27 Join Date: May 2007 Posts: 32 Location: User is: OffLine	Re: p0300 and p0420 codes help!!! random misfires are most likely caused by a vacuum leak.
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05-23-2009, 01:45 PM	#3
schveb Registered User Join Date: Apr 2009 Posts: 14 Location: User is: OffLine	Re: p0300 and p0420 codes help!!! Did you ever figure out your problem? I'm having the same symptoms with my 4.3l> I have changed distributor, wires, plugs, and cleaned my mass air flow sensor with no help. I haven't gotten a p0420 code yet but my cat rattles like the honeycomb is broken everytime i hit or let off the gas. Let me know what you found out! Thanks
	[Reply w/Quote]

05-24-2009, 08:38 PM	#4
2separate Registered User Join Date: Feb 2008 Posts: 161 Location: No place to hide User is: OffLine	Re: p0300 and p0420 codes help!!! It means, it's time to wave goodbye to your GM product.
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