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Discussion Starter #1
I have a 2003 5.3 sierra with about 128111 mi on it to be exact. I have been driving it around with the engine light on in the last few months. I ran a scanner on it and it came up with a heater curcuit and o2 sensors. Ive replaced the o2 sensor that was suppossedly bad and my engine light is still on after ive reset it. Now my engine light flashes at random times while driving or sitting at stop lights. I can drive for a week or even three without the engine light flashing and then one day the solid engine light will begin to flash. The truck runs worse when the engine light goes from steady to flashing. Since the light has been on the truck has had a rough idle and kind of lurches at stop lights. The mpg is horrible and im in need of some help quickly because i cant afford to pay for gas so often while trying to diagnose the problem. Im thinking it could be a fuel filter, injectors, plugs, or wires. I am very low on money though and my parents dont seem enthusiastic about helping me out, even though im only 17, so i dont want to do anything unecessary. I want to get it running well and get rid of the engine light that ive had to stare at forever. Thanks so much in advance for any help you can offer.:shake:
 

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kissin hands shakin babie
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run the scan tool again, a flashing CEL is for 02 sensors not working properly.

the 02 sensors tell the motor how much fuel to put in, so with one or more bad, it will dump tons of fuel to keep the motor from leaning out and burning up

CEL is your friend in this case because it tells you the exact problem read the codes, fix the problem, when the CEL is on, your mpg is going to go to shit
 

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Discussion Starter #3
ok thanks, thats new info to me so ill look into that. once i scan it ill let you know what codes i get.
 

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kissin hands shakin babie
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ok thanks, thats new info to me so ill look into that. once i scan it ill let you know what codes i get.
exactly, autozone and some places do it for free.

once you know the codes, like 02 sensor bank 1 sensor 1, then you know what you need to replace/check to make sure you are running right.

btw the more you run it like you are, the more your going to have a chance of getting a bad cat.
 

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Discussion Starter #5
yea im aware of the bad cat risk that im putting it at...would my CEL appear if a cat was bad too? i hope i didnt destroy the cats already
 

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kissin hands shakin babie
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yea im aware of the bad cat risk that im putting it at...would my CEL appear if a cat was bad too? i hope i didnt destroy the cats already
yea, but it would show up as a 02 sensor code, normally the o2 after the cat, and most people replace the 02 first because its cheaper then the cat.
 

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Discussion Starter #7
ok i see. will it still run like shit with a bad cat(s) and if i ran it with a bad cat(s) would my new O2 sensors be destroyed?
 

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AllOffTopic.com FTW!
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I ran a scanner on it and it came up with a heater curcuit and o2 sensors. Ive replaced the o2 sensor that was suppossedly bad and my engine light is still on after ive reset it.
Did you check the O2 heater circuit too?

What were the code numbers? There are plenty of codes that are related to O2 sensors, and if you just let the Autozone guy interpret the code for you then almost every code sells an O2 sensor.

Now my engine light flashes at random times while driving or sitting at stop lights. I can drive for a week or even three without the engine light flashing and then one day the solid engine light will begin to flash. The truck runs worse when the engine light goes from steady to flashing.
It's misfiring when that happens. You probably have misfire codes stored now.

yea im aware of the bad cat risk that im putting it at...would my CEL appear if a cat was bad too? i hope i didnt destroy the cats already
Yes, there are a few codes for bad cat. The most common is P0420 Catalyst System Efficiency Below Threshold (Bank 1).
 

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Discussion Starter #9
i honestly dont know what the O2 heater curcuit is:/ would misfiring be caused by the O2/cat related problems or do i have more issues at hand?

Thank you so much to everyone thats helped so far i really appreciate it!!!!
 

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My dad was having a similar problem to what you're describing on his '06 1500 w/ 5.3. He replaced ended up replacing both O2 sensors, and then got an error that he was running lean on both banks.

I suggested he clean his MAF sensor (which I had just bought a can of the cleaner for my '02), run a spray can of SeaFoam Spray through the intake (just hyperlinked the Vortec instructions), and then run a bottle of Castle Fireball injector cleaner though the gas tank.

It seemed to clear things up just fine for him, and no issues for 4 months now. Now I don't know if one was the key to the problem or not, but I wouldn't think its bad practice to clean all of the components out. I did it to my '02 1500 w/ 5.3 and it seemed to improve my mileage a bit.

Hope this helps for what it's worth.
 

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AllOffTopic.com FTW!
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The O2 heater circuit provides power to the O2 sensor so it can heat up more quickly. I'd guess you might have a nicked or corroded wire going to the O2 sensor.
 

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Discussion Starter #12
Ok, so ive replaced all three of my sensors, the two upstream and the downstream. The truck started up fine and began to idol rough at first and got a little bit better. It smelled worse than it had before i replaced the sensors though. After a few minutes I drove it around for a while and it seemed to be running fine. As I was driving i noticed that it seemed a lot smoother than it did before but it felt different, almost like it was loaded up, like a two stroke motorcycle loads up. While driving it i "cleaned it out" by throttling it a little more than usual and it seemed to help but then as i was turning back down my street the truck shut off while turning, allowing the engine to move the truck in drive at idle. I wasnt using the gas. So I started it up again immediately which it did so easily. This morning i left for school and i opened my garage and started the truck. The engine light came back on steady right away and white and light black smoke was puffing from the exhaust as the truck struggled to idle for a bit. I backed out of the garage because it was stinking up the garage and let it idle for a few minutes, the smoke thinned out more and more and the idle became stronger but it still only idles at just over 500rmps when it normally is around 1000. Although it seemed to be running worse than before based on all of these factors, while driving it seems to run much smoother and has not misfired once. I am going to replace the fuel filter today and see if that makes any difference as well as remove all of my plug and clean them with a wire brush. I just need to fix this soon because im out of money now after spending all of it on oil, an oil filter, the sensors, a window, and fuel filter, which to my knowledge, should have fixed the problem. Please if you can help me out do so in the best way you can:) thank you to everyone in advance in helping me with my truck
 

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JUGS Racing
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Get it scanned again to see why the light is back on. Also what brand O2 sensors did you use?
 

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cunts
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Sounds like a clogged cat :imo:
 

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Discussion Starter #15
I got Bosch sensors, I also have replaced all plugs and wires with new Bosch top of the line plugs and replaced the fuel filter. The idle has gotten better and the truck is running a little better but overall, it is the same, smoking black smoke from the driver side exhaust tip, only puffs out a little bit at idle. Its very faint but when I accelerate it pumps a little more out like off the line. It smells horrible and runs horribly, if I have to guess id say the smoke is a sign that it is burning oil??? I just don't know what to do anymore because I am 17 and 100% BROKE after spending money trying to fix the truck. I really hope I can fix it soon but i have no scan tool and no money, I'm getting so frustrated with it that i almost want to sell it but i can't because I've put too much time into it.:(
 

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kissin hands shakin babie
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I got Bosch sensors, I also have replaced all plugs and wires with new Bosch top of the line plugs and replaced the fuel filter. The idle has gotten better and the truck is running a little better but overall, it is the same, smoking black smoke from the driver side exhaust tip, only puffs out a little bit at idle. Its very faint but when I accelerate it pumps a little more out like off the line. It smells horrible and runs horribly, if I have to guess id say the smoke is a sign that it is burning oil??? I just don't know what to do anymore because I am 17 and 100% BROKE after spending money trying to fix the truck. I really hope I can fix it soon but i have no scan tool and no money, I'm getting so frustrated with it that i almost want to sell it but i can't because I've put too much time into it.:(
black smoke is raw fuel, meaning your running rich as hell.

autozone/oriellys ect will all scan the truck for free. but IMO i think you clogged the cats. when you ran it that long without good o2 sensors, it kept putting raw fuel into the cats clogging them
 

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kissin hands shakin babie
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also, no one with the right mind would buy your truck if it is running shitty, and if they did, they would not pay much. best bet, try to barrow a few bucks from the old man to get it together, and show that you want to work to pay it off
 

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Discussion Starter #18
Yea I know nobody would buy it like that haha, is there a way to clean the cats out or can I just run cat delete pipes until I have money for new ones? Thank you so much for your help.
 

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kissin hands shakin babie
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Yea I know nobody would buy it like that haha, is there a way to clean the cats out or can I just run cat delete pipes until I have money for new ones? Thank you so much for your help.
if you cut out the cats you will have it running better, but it will still have the check engine light on, because the rear 02 sensors will throw codes for bad cats.

to fix that, you can either tune it, $250, try to find simulators(?) or just put new cats in (not to badly priced if you do it yourself.)


but i would try to get the code read first, to make sure thats exactly what its for
 

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Discussion Starter #20
Yea, I can do it all myself pretty easily, is there a way to physically clean out the cats, I don't know what they are made up of so idk if they are cleanable.
 
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