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Discussion Starter #1
I am having trouble resolving trouble code P0304.

I am going to provide background information which only dates back 6 months when I purchased the 2009 Chevy Traverse 2wd with 134,XXX miles and a P0305 and ?P0420? fuel pressure too low bank1. I don't exactly remember the code.

I replaced the plugs with iridium plugs and all six coils. Cylinder 5 plug had lots of carbon build up. I found oil in the air intake filter box, around the plenum and so forth. I replaced the serviceable PCV system components and changed the oil.

Fast forward through heavy oil consumption and replacement to now where I have a P0304 that won't go away. I decided to replace the injectors, fuel rail pressure sensor, single use fuel line components, plugs and intake gasket. During the process I noticed more oil around the plenum but considerably less and none in the air intake filter box. I did however notice that the cylinder 5 plug was covered in carbon build up again with only a tiny dot of the electrodes surface area visible. Anyway, I assembled everything and the cylinder 4 misfire is still there. I swapped coils with cylinder 6 and the misfire remains in cylinder 4. The plug that I removed from cylinder 4 was black and wet with fuel indicating that the injector was in fact providing fuel so now with the new injectors, new plugs and and a confirmation that the coils are functioning I am at a loss and could use some insight.

Thank you in advance.
 

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what have you done about carbon build up on top of the valves?

It could also be carbon buildup on the sealing tip of the valves (sticky valves).

Try a bottle of techron concentrate plus. Hopefully this can clean up the carbon on the mating surface.
 

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Discussion Starter #3
I have run Techron through the system twice and I just added more with this last service to no avail.

I just completed a compression test and the results are not good.

cyl1 170psi
cyl2 175psi
cyl3 160psi
cyl4 0psi
cyl5 160psi
cyl6 170psi

From what I gather it is likely a valve issue. Does that sound likely?

Also, Cylinders 3&5 are side by side with 160psi, is this an indication of a head gasket issue? I understand that I'm getting into a lot more with cylinder 4 being dead but I'm still trying to gather knowledge.
 

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I would suspect the #4 valve has carbon buildup preventing it from sealing. As far as freeing it up before a top end cleaning, I have no ideas on how that would be performed successfully without getting debris into the cylinder. More research is needed on freeing one up, I am looking as well, please keep us updated as to what you find.
Also since you had the misfire, the cat had raw fuel going in, it may be clogged. Before you condemn any cylinder based on compression readings, see if you can disconnect the cat and re-test the compression.
I do need some clarification on using the Techtron. Even GM suggests using their cleaner which is essentially the same formula. On direct injection engines, the fuel doesn't touch, therefore, clean the valves. So how will using Techtron clean the valves if it doesn't get sprayed onto the valves. I use it occasionally but how does it do what they say it does. Just Saying.
 

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there was a member who had bad compression.
mechanic told him to get new/used engine and hed install it.

We told him it would not hurt to run techron and CRC intake valve cleaner.

well he did.
He came back over a year later and said the car was running GREAT.
he simply had several carbon.

THeres been recent threads of such intake cleaners loosening carbon- and subsequently causing increased oil usage.
due to carbon scratching the walls of cylinders.
Up to you.
But in this case-- you may want to do it- and well then look forward to increased oil usage wich will eventually get to all DI engines.
Or you can have walnut shell blasting to clean.....
 

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To help narrow things down, you can have a shop do a leakdown test on that cylinder. They should know this already, but if you hear the compressed air coming out of the intake/throttle body, then your intake valve is the culprit. If it's coming out of the PCV or dipstick tube, then it's more likely the rings. Coming out the tailpipe, then the exhaust valve.
 

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Discussion Starter #9
So I called the local Chevy dealer service center and spoke with someone about the issue and I dropped it off after hours. I ended up speaking to someone in the morning and they told me they would perform the service and have it ready in an hour. I then proceeded to explain that the procedure requires a few hours according to GM but they assured me that GM was wrong and that they've done this many times. I asked that they reread the instructions and perform the procedure accordingly but that of course lead to the service center employee getting frustrated with me. To make an aggravating story short, there is no difference in the vehicles performance however, they are willing to put the $148 service fees towards the purchase price of a new vehicle. I'm not even remotely convinced that the service was performed on my vehicle, let alone properly, so my experience may not be a proper review of the product but rather an experience with poor management.

My experience with vehicles...
'73 Plymouth Gold Duster 163,000
Sold - Driveable
'86 Ford Mustang 201,000
Junked - Transmission slipping
'93 Mazda 626 199,000
Junked - Faulty windshield replacement resulted in integral damage to the body.
'97 Ford F-150 348,000
Sold - Drivable
'03 Ford F-150 268,000 and counting
'09 Chevy Traverse 138,000
Junk - Not a one off issue but an issue that affects a large portion of the production vehicles with this engine, over several years at least, in a wide variety of GM vehicles.
 

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maybe the person you talked to was thinking Fuel injection cleaning? vs top end ?
 

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Yes GM is wrong, NOT. The dealers and the Dealer Mechanics are used to billing the book rate hours but the mechanics have learned to take shortcuts and get the job in and out fast. The way they get make money, is to perform several jobs booked at 2-4 hours and get them done in 1-2 hours.
Take a headlamp replacement on these vehicles, book says to remove bumper, book hours 2 hours. The mechanics just peel back the wheel well cowling and are done in 15 minutes, but get paid 2 hours.
No wonder people get frustrated with Dealers.
What does the service ticket say about what your concern was and service was performed? The ticket usually says something like "Customer Stated" blah blah blah.
If they did the Top end cleaning it would have taken at least 3-4 hours of book time, the mechanic could have been doing other jobs as the cleaner was soaking.
 

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Discussion Starter #12
Service ticket states, "perform engine decarb service as per recommended maintenance schedule. Engine decarb service completed."
 

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Discussion Starter #13 (Edited)
I have been doing some poking around online and I have found dozens of instances where people have removed the valve cover and used penetrating lubricants and a hammer to tap on and free a sticky exhaust valve but none specific to this engine. I know nothing about how these valves function or their accessibility with overhead cams and so forth, does this sound like a reasonable approach to free the valve? Or would I not have access simply by removing the valve cover? I read an interesting article from an aircraft mechanic who pointed out the sticky valve issue in one of the two engines available on the particular airplane he was servicing. One engine operated at much cooler temperatures and as a result didn't have carbon buildup on the valves while the other engine had internal combustion temperatures averaging 400⁰ hotter and as a result the carbon would build up causing a sticky exhaust valve. He pointed out the symptoms to watch for to catch the issue before a seizure occurs in flight and offered a walk through to resolve the issue. Remove the valve cover and rocker, apply a dab if Marvel on the stem of the valve and tap the valve until it is free. Attach a string to the valve and lower it into the cylinder and hone the valve bore to free it from carbon. I'm not suggesting that I would go through this entire procedure but if I could free up the valve enough to get it to function then hopefully I could get combustion in the cylinder and do a proper decarb. Obviously I don't know too much about heads and values so if someone else does, am I grasping at straws here?
 

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I would be very leery of doing something like that. I believe that the carbon deposits are pretty hard and abrasive. When these particles dislodge and get into the cylinders, who knows what will happen. I was reluctant to use the CRC cleaner but after seeing that GM recommends a similar procedure to combat the buildup, I decided to do it. The cleaner soaks in a softens the deposits.
I wasn't having any major issues. My issue is an extended crank and is one of the possible symptoms in carbon buildup possibility. Using the CRC, I didn't notice any better performance, or did it fix the extended crank. I have a new Purge valve which I am installing today, hoping it will correct the cranking.
My mileage has improved since using the CRC valve cleaner but I also use Techtron every few tankfuls, so I have no idea which cleaning contributed individually or was combination of cleaners which helped. My oil consumption is pretty good, about a quart every oil change, I do not let the OLM go to zero and I use Full Synthetic.
Valvoline makes a new oil, For Modern Engines, which supposedly combats carbon buildup, I don't know if it will clean existing carbon.
 

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Service ticket states, "perform engine decarb service as per recommended maintenance schedule. Engine decarb service completed."
I don't see a Decarb Service as per recommended maintenance schedule in a 2009 or a 2015 owners manual so it must be a dealers cash cow thing. I saw one procedure which said to let cleaners soak for 30 min. CRC and GM cleaners say to let soak for 2 and 2.5-3 hours respectively. I guess the dealer does it the short soak way. Maybe they did what you asked them to but their own procedure which they are used to, not the official GM procedure.
If I were you, I would try the CRC cleaner, a bottle of Techtron, Top Tier Gasoline and change the oil in a week of normal driving.
 

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Discussion Starter #16 (Edited)
I had been too busy to tear down the engine so I bought another work truck and let my wife drive it for awhile until I could get into the engine, which ended up being yesterday after months of researching and learning that I would need to pull the engine to service anything more than spark plugs or an oil change. Removing the valve covers without removing the engine would be more difficult than it's worth, if not impossible. Anyway, I got the heads off and the first thing I noticed was surface rust in the bore of cylinder 4. Then I looked through the remaining cylinders and I didn't see any scoring in the cylinders which I was expecting from the dislodged carbon deposits resulting in heavy oil consumption. In fact, I could clearly see the crosshatch marks from when the engine was originally machined. So next I went to the heads where I found a lot of carbon buildup on the face of the valves but not much around the seats. I did however find a hole in one of the exhaust valves on cylinder 4 which explains the loss of compression in that cylinder as well as the rust in the cylinder as moisture could then pass through the exhaust and into the cylinder while the vehicle sat. This is not some tiny pin hole that I found after an exhaustive search but rather a glaringly obvious hole that resembles Jerry's home door from Tom & Jerry. What's more, I can't figure out where the particles of metal have gone. Again, there was no scoring in the cylinder that would indicate that a large chunk of the valve fell into the cylinder. The honeycomb in the catalytic converter didn't have any buildup or pieces of anything in it. It was slightly darker in color than the cat from the opposite side but still looked relatively clear. Light passes through without obstruction when I shine a flashlight through it. I'm wondering if the valve deteriorated over time with the particles being so small that they passed through the cat without being lodged into it.

There is a noticeable rim or step in the bore of cylinder 4 where the piston ring and cylinder wall sat in contact with each other while sitting and the rust developed so I will have the block bored before rebuilding it. I'm also going to dismantle the heads and leave them in a Crockpot with antifreeze overnight to descale the carbon before inspecting them to determine whether they need to be machined. (A slow cooker with antifreeze will clean carbon from engine components with remarkable results for those unaware.) As a note, some valves have rather excessive amounts of carbon buildup while others don't. There is no uniformity as far what valves have more or less buildup than others. Some have buildup on one or both exhaust valves, others it's the intake valves while all four valves on cylinder six are caked. No surface area of the heads or pistons show any signs of carbon buildup so new guides and valves might be all the heads need.

There was plenty of evidence to suggest that the engine was previously removed including missing gaskets behind the timing cover and plenty of rtv in their place. It held up fine but I can't figure out why someone would go through the trouble of doing a timing chain and not spending a few extra dollars on gaskets. Well, the vehicle has 141,××× miles and the body and undercarriage are immaculate so I feel that the rebuild is warranted.

I appreciate all the input from the numerous threads here and throughout other forums so I wanted to do an update with what I've found.
 

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I'm just curious, do you think you economically rebuild this motor vs just finding a junkyard replacement? My concern would be in your plan to have it bored to address the cylinder wall damage - I do not know the 3.6's well, more of an LS guy but there is likely a limitation on a safe overbore on the iron liners. On LS's most will only go with a clean up hone or 0.010" at the farthest but that leaves no room for a future clean up hone. Other issue will be I don't think anyone makes a custom sized piston for a 3.6, and I'm sure if there's a solution it will be quite expensive. These are a bit different then the old days of going 0.030" over on an SBC and bolting it back together with off the shelf parts.

There's enough Traverses out there I'm sure you could find a pull out LLT for a better price.
 

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At the very least you should contact GM and discuss this issue further. Who knows, maybe they had a bad batch of valves and will experience or have experienced this condition. They may even work out some kind of compensation or at least hopefully they will investigate the cause.
 
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