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Discussion Starter #1 (Edited by Moderator)
I have a 2012 GMC Acadia I've owned since new with 199,965 miles on her. I have taken very good care of this vehicle with oil changes every 6k miles with all other normal maintenance being done. I changed out all of the suspension, alternator, all cam shaft sensors, crank shaft sensor, cats and oxygen sensors myself. I am now in a chase the demons mode at this point over the last several months. The cats and Oxygen sensors were just replaced. The main issue I have now is that it is still running really rich and is throwing the P0420 and P0430 codes. Outside of the high pressure fuel pump, injectors and coils there's not much left to replace.

My symptoms at this stage are black smoke and strong odor at start up, lack of real power, occasional rpm jump, stutter at speed from time to time.

Please Help!!

(mode edit - spelling and code nomenclature corrections)
 

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Sometimes after over 100K or 150K miles on a vehicle, it's better to think about a newer one.
I know a lot depends a lot on a person's personal economics, but part of owning using a vehicle to higher mileage is to save some $$$$ for the next vehicle when needed. At least, that has been my habit in years gone by.
Now I drive fewer miles and just try and practice good maintenance.
 

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My symptoms at this stage are black smoke and strong odor at start up, lack of real power, occasional rpm jump, stutter at speed from time to time.
You mention nothing about doing a carbon cleaning of the engine. Sometimes a good cleaning (chemical or physical removal) of carbon deposits will resolve the described problems. GDI engines are notorious for running poorly because of carbon build up. If the carbon contaminates injector tips, fuel won't atomize or combust properly, resulting in an impression the engine is 'running rich.' Carbon can also cause loss of compression and engine power if there's too much of it on the valves and cylinder heads. It's worth trying in this case - much better than throwing parts at a problem. You can also clean the MAF sensor and check/replace the air filter when you do that.
 

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Discussion Starter #4
Thanks Speleos and yes I have cleaned the MAF sensor and I have a K&N air filter that was just cleaned. I have done a couple of carbon clean outs but the top of the lifters are nasty dirty. I will say that the first time I cleaned it with CRC and after it got soaked I blew a bunch of smoke out and then for 1 day it ran like a new car. Could this then possibly be dirty injectors? What might be your suggestion on another carbon clean, especially for the dirty lifters.
 

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... What might be your suggestion on another carbon clean, especially for the dirty lifters.
That would be physically cleaning the valve with a walnut shell blaster if the chemical didn't work well enough.

Could this then possibly be dirty injectors?
Dirt is almost never a problem inside a fuel injector, unless there's contamination of the fuel supply. When anything accumulates around the injector nozzle (outlet), this deposit can disrupt the spray pattern and create droplets of fuel which are more difficult to 'burn.' Most often, a fuel injector cleaner added to the fuel tank will remove that dirt and allow the fuel to atomize the way it should.

They could be getting weak. This happens when the pintle return spring wears out, or the electromagnetic coil (solenoid) begins to fail. Then, they'll start leaking fuel from the outlet and introduce too much of it into the combustion chamber.

9190
 

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Good thing you didn't hit anything else while taking the pic. LOL
 

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Make sure the injectors aren't leaking in that bank and that you have no exhaust leak before the O2 sensor. It actually running like garbage suggests that if there was an exhaust leak it would be before/close to the front/first O2 sensor on that bank as that determines the a/f ratio. It running rich should have nothing to do with valves as there should be no fuel there if the valves aren't closing all the way due to carbon, assuming the injectors are ok.

I've had a p0420 due to a leak further down the pipe, but that didn't effect the performance/fuel ratio.

Were the cats replaced before the codes or after? You should never (in general) replace a cat for this code. A rich running motor will kill the new cat.
 

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My wife's car is a 2012 also. It runs rich when first started cold. Misses and I can see black unburned fuel smoke out the tailpipe. It will clear up in like one minute, but I wonder if its a problem I don't have a check engine light on.
 

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My wife's car is a 2012 also. It runs rich when first started cold. Misses and I can see black unburned fuel smoke out the tailpipe. It will clear up in like one minute, but I wonder if its a problem I don't have a check engine light on.
Engines generally run rich during a cold start. Fuel-injected engines are 'choked' by the electronics much like a carbureted engine is choked with a butterfly plate. That black smoke on start-up you're seeing is fairly commonplace with GDI (gasoline direct injection) engines.
 

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The original 3.6L Gasoline Direct Injection GM engines do run rich the first 60 seconds or so intentionally.
This was a design choice to make for a quick warm up of the catalytic converters so that they can fundtion more quickly.
Astounded me also, that they would design a rich condition initially so that later it would pollute less. LOL
See attached LINK: - - https://static.nhtsa.gov/odi/tsbs/2015/MC-10114908-9999.pdf

- " A dual-pulse injection strategy is utilized during engine cold start to reduce the time required to bring the catalytic converter up to operating temperature.This split injection strategy lasts for about 60 seconds on cold start.This process will cause the customer to see increased black smoke, soot, rough idle, or minimal misfires during cold start and should be considered normal " -
 

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Astounded me also, that they would design a rich condition initially so that later it would pollute less. LOL
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Have you ever tried starting any internal combustion engine with an air/fuel mixture which was leaned out too much - like to normal "lean best" (warm) idle mixture? It doesn't work really well - crank, crank, crank, crank, crank, ..., ...! 😱 Interesting thing is that diesels and turbines will tend to blow bluish smoke during a cold start because of their rich condition.
 

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My wife's car is a 2012 also. It runs rich when first started cold. Misses and I can see black unburned fuel smoke out the tailpipe. It will clear up in like one minute, but I wonder if its a problem I don't have a check engine light on.
Not a problem if no CEL.
 

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Have you ever tried starting any internal combustion engine with an air/fuel mixture which was leaned out too much - like to normal "lean best" (warm) idle mixture? It doesn't work really well - crank, crank, crank, crank, crank, ..., ...! 😱 Interesting thing is that diesels and turbines will tend to blow bluish smoke during a cold start because of their rich condition.
I have. Have you ever ever tried starting a car like we did every cold winter morning back in the day with 2 bbl carbs and manual or automatic chokes? Nothing new to me about that. . . . LMAO
Of course the A/F mixture needs to be richer on a cold start, so good to know that you know that. LOL🤣

The point is , , , the 3.0L and 3.6L V6 engines GM built and used (like the one you have) as mentioned in the TSB I posted were abnormally rich compared to the newer LGX and LGZ 3.6L engines. Very little tail pipe black soot or exhaust on a cold start on the newer 3.6L V6 engines due to having the cats integral and closer to the engine exhaust path as well as better fuel injector management.
 

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I have. Have you ever ever tried starting a car like we did every cold winter morning back in the day with 2 bbl carbs and manual or automatic chokes? Nothing new to me about that. . . . LMAO
Of course I have, DA. I've owned cars from the '50s and '60s. Probably have operated a more diverse portfolio of vehicle/engine types than many on this forum.

... the 3.0L and 3.6L V6 engines GM built and used (like the one you have) ...
Not in my Acadia, SA. The '07 doesn't have DI. It gets a whole lot less exhaust soot.
 
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