problem, help please...
07-11-2009, 12:58 AM
#1
problem, help please... ok, so I've tried discussing this a few times with people, but I've never gotten a clear answer..
i have a 1997 camaro z28 with a mostly stock motor.
it's throwing P0300- "random multiple misfire"
when started cold i get no misfire, but once the car warms up i start getting a miss that i can hear through the exhaust.
i was told this seems to be a "open/closed loop" problem, which would bring it to the MAF or 02's. well the MAF is new along with plugs, wires, IAC, TPS, and EGR.
Could this indeed be my O2 Sensors?
and shouldn't the car throw a code for the sensors themselves?
Help please, this is bugging the living **** out of me...
i have a 1997 camaro z28 with a mostly stock motor.
it's throwing P0300- "random multiple misfire"
when started cold i get no misfire, but once the car warms up i start getting a miss that i can hear through the exhaust.
i was told this seems to be a "open/closed loop" problem, which would bring it to the MAF or 02's. well the MAF is new along with plugs, wires, IAC, TPS, and EGR.
Could this indeed be my O2 Sensors?
and shouldn't the car throw a code for the sensors themselves?
Help please, this is bugging the living **** out of me...
07-11-2009, 10:59 AM
#4
it "Should" be throwing oxygen sensor codes if that were the case... It could be and sounds like it though...
get a friend w/ a f body and see if you cant use his oxygen sensors for a second and see if it fixes it..
sure does sound kind of like an opti KIND OF does it mainly misfire in high rpms or just all the time once its warm? When my oxygen sensors were bad it would misfire at partial throttle the whole time but when i gave it wot it would run alot smoother.
get a friend w/ a f body and see if you cant use his oxygen sensors for a second and see if it fixes it..
sure does sound kind of like an opti KIND OF does it mainly misfire in high rpms or just all the time once its warm? When my oxygen sensors were bad it would misfire at partial throttle the whole time but when i gave it wot it would run alot smoother.
07-11-2009, 11:16 AM
#5
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well, does it miss at Wide Open Throttle? Computer ignores O2 readings on wide open throttle.. easy way to diagnose that, or unplug them and see if it changes anything
07-11-2009, 11:50 AM
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How about the dist. cap or the actual pickup in the opti? Sounds like a better reason than an O2 ever would on an LT engine. How many miles are on the original equipment or has it been changed out?
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07-11-2009, 03:12 PM
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07-11-2009, 09:28 PM
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An O2 really should not have enough effect to cause multiple cylinder misfires, both rarely ever fail at the exact same time. To effect both banks it would have to, I am really betting on ingnition problems
07-11-2009, 10:51 PM
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can you see the o2 sensor values with the scanner you used?
07-12-2009, 12:27 AM
#11
well this is throwing me in two different directions.. what in fact could this be guys.
i cannot read the values with the scanner, plus i have to drive the car the the auto parts store to use it every time i need to read codes, it's really annoying.
as far as WOT the car runs great, still fast and i can't tell that there's a misfire whenever i'm pounding on it, but at idle i can hear it in the exhaust.
now if i'm just driving the car like normal and i have the cruise set at say 55mph, and then the the cruise starts to counter a slight hill by giving throttle to keep speed up the hill the car vibrates/shakes like it's misfiring.
i cannot read the values with the scanner, plus i have to drive the car the the auto parts store to use it every time i need to read codes, it's really annoying.
as far as WOT the car runs great, still fast and i can't tell that there's a misfire whenever i'm pounding on it, but at idle i can hear it in the exhaust.
now if i'm just driving the car like normal and i have the cruise set at say 55mph, and then the the cruise starts to counter a slight hill by giving throttle to keep speed up the hill the car vibrates/shakes like it's misfiring.
07-12-2009, 01:57 AM
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ok, so I've tried discussing this a few times with people, but I've never gotten a clear answer..
i have a 1997 camaro z28 with a mostly stock motor.
it's throwing P0300- "random multiple misfire"
when started cold i get no misfire, but once the car warms up i start getting a miss that i can hear through the exhaust.
i was told this seems to be a "open/closed loop" problem, which would bring it to the MAF or 02's. well the MAF is new along with plugs, wires, IAC, TPS, and EGR.
Could this indeed be my O2 Sensors?
and shouldn't the car throw a code for the sensors themselves?
Help please, this is bugging the living **** out of me...
i have a 1997 camaro z28 with a mostly stock motor.
it's throwing P0300- "random multiple misfire"
when started cold i get no misfire, but once the car warms up i start getting a miss that i can hear through the exhaust.
i was told this seems to be a "open/closed loop" problem, which would bring it to the MAF or 02's. well the MAF is new along with plugs, wires, IAC, TPS, and EGR.
Could this indeed be my O2 Sensors?
and shouldn't the car throw a code for the sensors themselves?
Help please, this is bugging the living **** out of me...
07-12-2009, 01:59 AM
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07-12-2009, 02:06 AM
#16
ok, so i unplugged my o2 sensors and it's still misfiring, but still only once it warms up. it doesn't seem as bad either.
but if it's been running with bad o2's wouldn't that foul the plugs causing it still to misfire?
i haven't checked fuel pressure or for vacuum leaks, but i don't think i have a vac leak, cause the car idles perfectly. i don't have a scanner, and those are really price too. what Values do i need, i might be able to get them from the scanner at advance auto?
BTW I've had this problem for quite some time now, and have had no luck fixing it.
the car as a reg cutout on the exhaust right under the back seat bucket, last week i ran it with the cutout closed and the code went away and it didn't misfire, but then i took the cap off the cutout and drove it a bit and it started again, wtf.
but if it's been running with bad o2's wouldn't that foul the plugs causing it still to misfire?
i haven't checked fuel pressure or for vacuum leaks, but i don't think i have a vac leak, cause the car idles perfectly. i don't have a scanner, and those are really price too. what Values do i need, i might be able to get them from the scanner at advance auto?
BTW I've had this problem for quite some time now, and have had no luck fixing it.
the car as a reg cutout on the exhaust right under the back seat bucket, last week i ran it with the cutout closed and the code went away and it didn't misfire, but then i took the cap off the cutout and drove it a bit and it started again, wtf.
07-12-2009, 02:18 AM
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ummm just throwing one thing out. if you do pull the plugs off the 02s again pull the battery off the car for 2-3 hours. when you start the car back up with the 02s unplugged it will relearn the car and how its running. and do the same for when you plug them back in. i honestly think just pulling the battery for a while will help just due to the simple fact the computer will relearn the whole car over again. i did it on my 383 and it ran completely different not exactly in the best way but a few problems arose lol but none the less. just my two pennies
07-12-2009, 02:18 AM
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so it did improve? i think it would be a good idea to put some miles on it. things should clear up after that if it was the problem. you have to understand that its tough to fix this without looking at those values with the scanner.i would first start by looking at the o2 sensor values. if they change very slow then you know you have a problem. i would still check the simple stuff like fuel presure.does it still misfire going up a hill?
07-12-2009, 02:23 AM
#19
ummm just throwing one thing out. if you do pull the plugs off the 02s again pull the battery off the car for 2-3 hours. when you start the car back up with the 02s unplugged it will relearn the car and how its running. and do the same for when you plug them back in. i honestly think just pulling the battery for a while will help just due to the simple fact the computer will relearn the whole car over again. i did it on my 383 and it ran completely different not exactly in the best way but a few problems arose lol but none the less. just my two pennies
so it did improve? i think it would be a good idea to put some miles on it. things should clear up after that if it was the problem. you have to understand that its tough to fix this without looking at those values with the scanner.i would first start by looking at the o2 sensor values. if they change very slow then you know you have a problem. i would still check the simple stuff like fuel presure.does it still misfire going up a hill?
I guess I'll drive it around tomorrow and see what happens. How do i check the o2's values with the scanner, that's what i'm not understanding, and how do i check fuel pressure? and yes, it shakes and vibrates under partial throttle going up a hill, so i'm pretty sure it's missing up the hill.
07-12-2009, 02:34 AM
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well not all scanners can do it. some of them are cheap and only read codes. a good one
will have different menus to select from and will have it under actual values. it should be under the powertrain section and some will have it under 2 options. one for engine and one for transmission. there is a port at the back of the intake near the egr where you can hook up a fuel presure gauge. it has a black plastic cap that you twist off.
i would also recomend getting a repair manual from the parts store if you dont have one.
does it missfire going up a hill when the engine is cold?
will have different menus to select from and will have it under actual values. it should be under the powertrain section and some will have it under 2 options. one for engine and one for transmission. there is a port at the back of the intake near the egr where you can hook up a fuel presure gauge. it has a black plastic cap that you twist off.
i would also recomend getting a repair manual from the parts store if you dont have one.
does it missfire going up a hill when the engine is cold?
