P300 Random missfire

Hello all,
First post here but i got a major probelm i can not figure out here. My 96 chevy blazer will run/idle fine for about a min then it runs reall rough and service engine soon light comes on and the whole car shakes (Misfireing) then diffrent times it goes away and will run just fine untill i turn off my car and it repeats it slef. The amount of time it runs rough depends i dunno on what though some times for like 5 mins some times for like 30 sec dunno. Also when its warmed up it seems to happen faster and get over faster then if its cold like in the mornings. i also have a bad o2 sensor bank 1 umm i think its p146 i am not for sure. But any advice would help. i changed the router and distributer cap and i still haveing problems it just dosen't seem like it would be plugs or wires becuase after i run it for a lil bit it does just fine and never have a problem again untill i turn it off and have to start it back up ( For example like getting gas)

Ok i would apprecate and help on the matter i need my car better and i don't have alot of money (like anyone has alot of money to through into a car lol) ok thanks

Matthew

Welcome to AF. You mentioned you have a bad 02 sensor. Has this been looked after? This could very well be the problem.

When you first start it up, like in the morning, does it run alright, take a few seconds,maybe a minute, runs bad, then SES light comes on and it runs alright again? If this is the case could verywell be an O2 sensor. the sensor is not used when the truck is first started, it has to get warmed up, then the system goes into closed loop, and sensor readings are used to control air to fuel ratio. When the O2 sensor is bad, it gives the computer inaccurate readings, the system tries to correct itself, realizes the readings are out of whack, and throws the SES light, and maps predetermined(built-in) values, , using other sensors information also. In this case the truck is still drivable.

DTC P0146 HO2S Insufficient Activity Bank 1 Sensor 3

ok, on that o2 sensor i think it came on about the same time it started haveing problems. The ses light first said that it had high voltage and now it says something like its nto active or not found or something like that. I have been getting mixed opinions on weather this o2 sensor could be the problem. some say yes some say no. when its cold it runs fine for about 1 min then have problems but still idles just fine just car kinda shakes then it will be fine after that.

Thanks for the fast reply, Matthew

. when its cold it runs fine for about 1 min then have problems but still idles just fine just car kinda shakes then it will be fine after that.



yeah, this sounds like an 02 to me.

How for sure are you just don't want to dump money into a vechical and that not be the problem i am not trying ot doubt you i just don't have alot of money thats the only thing. i am currently rebuilding 1973 ford 360 and its drained me so i am trying to save my money. i have had to put off the engine because its costed me more then i thought it would.


Thanks

Matthew

Seeing I havn't actually seen or touched the vehicle myself, I can only make a honest observation, given what information you have put up on here. From what I have read on here, and given you already have a SES light on for an O2 sensor, I am confident that this verywell is your problem.

Ok i really appreacate all that you have done. Thanks again

Mathew Lowrie

Anyone want to back him up?
THX a bunch

Matthew

No problem at all, thats what everyone is on here, to help eachother and share information/experiences, goodluck!

in my experience when you have a misfire code, the o2 sensor for the bank that is misfiring will also throw a code because of the fuel not being burned right.

the o2 sensor code is IMO a symptom of the P0300 code, and not the cause.

I would look at putting the truck onto a scan tool and checking the operation of the MAF, TPS, IAC, EGR, and cam position/crank positions sensors if equipped (I'm not sure on your truck if it has one or both, or none).

Does anyone have any else have any input on my situation. I want to thank everyone for replying but still haven't gotten the o2 sensor because i just wanted some more opinions if possible. Thanks Again

Matthew