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  #1  
Old 04-06-2009, 09:48 PM
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Default P0300 code and P0420 code 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

PLEASE HELP thanks

Last edited by 98blazr; 04-06-2009 at 09:51 PM.
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Old 04-07-2009, 06:37 PM
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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?
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Old 04-07-2009, 06:51 PM
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If you do not know the last time a general tune up was performed, it would not hurt anything to do one.

But you really should diagnose the problems. Those threads I linked to go over a lot of tests that can be done without investing much over your own time. Please use that information rather than just taking the shotgun approach to auto repair.
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Old 04-07-2009, 10:23 PM
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well idk when it had a tune up besides changing oil and regular stuff like that i do that but as far as plugs wires etc i have no clue when and if it has been changed befroe, i just need a good direction to turn to in fixing it i dont have alot of time and or tools to test the electrical stuff i drive it daily and need to get it fixed asap..any ideas on a easy way to change plugs i know they are a pain*
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Old 04-08-2009, 08:08 AM
 
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ive had it where the plug wire has worn through and it grounds out on whatever it touchs as you drive. which resullted in a very poorly running motor at certain times or all the time. i would do a basic tune up. inspect your old wires for signs of decay or cracking. Also pulling your plugs is a very good way to see whats going on, inspect the plug for carbon deposits and the like. the spacing on the plug could be warped..... good luck
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Old 04-08-2009, 08:23 AM
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I'm going to check something you might want to. The fuel pressure regulator. There's a how-to here showing how to see if it's bad. I have the same experience you do. Rough in the morning and clears up as the day goes. Also the colder it is the worse the start off. Try that first. It's easy but the little bugger costs $42.
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Old 04-09-2009, 10:15 AM
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well yesterday i unhooked my battery and let it sit for an hour or so and hooked it back up to reset the computer and the engine light stayed off when i started it up. but if i reved it up to 2k rpms or higher it sputtered missed and would barley run so i just shut it off and about 2hrs later i had to go somewheres so i drove it and it didnt miss or sputter not once on take off or cruising speed. idk why but im sure its goin to start doing it again today

i checked the plug wires they looked new but i went ahead and bought some bosh platium plugs and new wires and rotor button i guess once it starts doing it im goin to try puttin those in and see what happens
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Old 04-09-2009, 11:55 AM
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You can check for spark leaks through the wire insulation with a spray bottle of water and a nice dark place to run your truck. With the engine running, mist the water over the engine. If you get a light show, the wires are bad.
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Old 04-09-2009, 04:51 PM
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lol a light show ?? sounds dangerous lol ill try it but today it was barley missing so i went ahead and put the rotor button on and it aint done it yet but i will see in the mourning
Old 04-09-2009, 04:51 PM
 
 
 
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1996, 1998, 96, 98, bank, blazer, catalyst, chevy, cylinder, detected, efficiency, misfire, multiple, p0300, p0420, po420, random, s10, system, threshold, truck


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