Black Smoke Issue!!!

[coryhussey]

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

[Taz]

Hello Cory,

I have stated this before in the Forum, and it is worth repeating - in a basically stock engine, there is very little performance to be gained by removing the catalytic convertors. There are many high flow cats on the market today that work well – even with modified engines. Cat technology has progressed a great deal in the last decade – removing the cats “just because” is an outdated and irresponsible approach – not to mention illegal. Unless this is a dedicated competition vehicle (permanently off road) – which it is not – running cats is a sensible and responsible course of action.

Regarding your problem …….

With a basic misfire, a typical diagnostic approach would include:

check for vacuum leaks
check for fuel contamination
confirm fuel pressure
confirm injector function
confirm coil function
confirm continuity of grounds (PCM / sensors)
CASE relearn if necessary

However, in this instance you described a massive amount of smoke coming out the tailpipe. Excessive smoke coming out of the tailpipe of a gasoline engine, with a sudden onset (not slowly increasing over time) is often indicative of a mechanical failure.

Regarding the colour of the smoke, the following are general guide lines for diagnostic avenues:

white smoke = coolant present in the combustion chamber
blue smoke = oil present in the combustion chamber
black smoke = excessively rich AFR

Check the spark plugs – are they oil fouled, or very “clean” (like they’ve been steam cleaned – from coolant) ? If either (or both) of these conditions exist, start suspecting a head gasket failure. Conduct a compression and leak down test of all cylinders. During the leak down test, remove the radiator cap and look for any bubbles in the coolant, also remove the oil fill cap and listen for escaping air.

The results of these tests should address a mechanical failure – head gasket, piston rings, valve guide / seals.

If these diagnoses to check for a mechanical failure are negative (nothing broken), attach a WBO and confirm actual AFR versus commanded AFR while operating the engine. For the kind of smoke you’re describing to be strictly a fueling issue, your AFR would be in the single digit range.


Good luck …..


Regards,
Taz