coryhussey

iTrader: (2)

Hey guys, i currently have an 03 sierra 5.3. I have had a efilive tune for a few years now. Current mods, volant cai, 03 z06 cam, dynatech long tubes with gutted cats. I recently tried to put a set of cats on the truck to pass my upcoming e-test. After putting them on the truck started running like a bag. It had no previous issues. I have tried cleaning and checking the MAF, throttle body, checked the FPR. The code it throws is po300. Random cylinder misfire. The check engine light usually flashes when i drive now. When i really get on it hard, it looks like a diesel with a programmer on it. The black smoke out of the exhaust is terrible. It also spews an oily black water out of the tailpipe. I ended up gutting the cats, because they were the improper cats. They were for a 4cylinder car/6cylinder car. Now i have no idea what it could be at this point. I cleaned the 02's as well. The front ones are turned off. I thought gutting the cats would fix the problem, guess not. I am changing the plugs tommorow, just wondering if anyone has experienced the black smoke that is plaguing my daily commute. Thanks

cory

baSICK5.0

iTrader: (1)

Im no expert but seems that your Black smoke means lots of fuel not getting burning. its super RICH. the oily black water is just condensation in the exhaust mixed with the soot of the exhaust. The black "water" is nothing to worry about. However the black "smoke" is.
I would think this would be a O2 sensor issue as they take constant reasding of your A/F ration and inturn your computer regulates the ratio by adding or removing fuel.

Dont continue to drive your truck if you can literally see the "black smoke". When you run an engine that rich and drive it you run the risk of washing down the cylinder walls, thinning your oil and hurting your motor, frying your rings, etc.

I say get it to a tuner quick.

Atomic

iTrader: (42)

You turned off the front O2 sensors? Those are the ones you need, its the rears that only check the cats.

coryhussey

iTrader: (2)

yea i just realized i turned the rear two 02's off. not the front ones. I am trying to narrow the problem. It is either the 02's or the maf.

FarmTruc

iTrader: (5)

If you have a scanner, check the o2's to ensure they are toggling up and down, from 50mv to 900mv.
If they are staying around 450mv, that's the problem.
What happens is, the pcm is detecting a lean condition so it dumps fuel until the o2 reads correctly, since the pcm will never add enough fuel to make the o2 read correctly (if the o2 is bad), it will continue to add fuel, hence the rich condition.
that is just one thing that might be happening.

kostelacd69

iTrader: (4)

Also if you have a scanner or efi live you need to check fuel trims. If your truck is still programmed to go closed loop or semi closed loop you will be able to see fuel trims. The ones you want to look at are the stft on both banks. You should see no more than +/- 5 some times as much as 8. If the truck is idling watch the fuel trims with ac off ect. It can take up to a min for the stft to acctivate. Watch those for say 3 mins with the truck at opp temp and reply with what you find.