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I am sorry guys, I think I have read all of the misfire threads on this forum and there seems to be a million of them. I finally signed up to get my question in since everyone seems so helpful on here. Here we go.

2011 Enclave CXL2 180k miles

Cylinders 1 4 6 are misfiring seemingly constantly. Using the Tourqe app I just watch these three cylinders add up the misfires. What makes this very weird to me is how it is split between the two banks. Timing chains, Spark plugs, Coil Overs, fuel rail pressure sensor, serpentine belt, and PCV valves all have been replaced in the last couple of months, the Coil Overs and the fuel sensor were done in troubleshooting later. After all of this work was done the car ran like a brand new one for 2 weeks after. Then it started misfiring and I pulled the codes and it was random misfires on all cylinders. I then decided to replace the coil-overs after reading several posts about them turning out bad after the timing chains were done. This didn't help so I broke down and took it to a mechanic I trust completely but he specializes in Volvo. He was able to confirm timing, compression, and no vacuum leaks he could find. He is convinced it is in the fuel system but before we spent the money to replace the fuel injectors and/or the HP fuel pump he wanted confirmation from a dealership. I ate my pride and paid the $150 for the diagnostic fee only to really regret it. I know they don't do much to diagnose but by pulling the codes they said that I had to replace all of the injectors and the timing chains just to be able to test the HP fuel pump with no other explanation. I am not dumping another 5k into this car just guessing at the issues. I am not a full-time mechanic so this has gotten a little too deep for my troubleshooting. It seems to me that if the timing was off it would not be so consistent on cylinders 1 4 6. Since getting it back from the dealership I have swapped cylinder 2 and 4's coil overpacks with no change and then the spark plugs with no change. Does this point directly to the injectors? I have already bought my wife a new car, but I am so frustrated that no one can seem to figure this out. I would love to be able to get this fixed so I can pass it on to someone else as a reliable option. I have only owned cash cars for the past 15 years because I can work on them and keep them running forever and until now I have never been stumped by a car.
 

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2015 Enclave Leather.
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Just a stupid question. What spark plugs were used in replacing. Non OEM or better plugs do not perform well on these engines. Also what kind of oil is used, synthetic or Dino and has it been changed regularly, any sludge build up? Oil level and distribution has a lot to do with the timing on these high feature engines.
 

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Discussion Starter #3
The plugs are Bosch Titanium. Oil has been changed regularly since I have had it, but I got it with over 100k on it, with just old fashioned dino 10w30 or 5w30 here in Texas. I changed the oil and oil filter when I replaced the chains. If it was still timing wouldn't it be random misfires on all cylinders, or dedicated to a bank? Should I use Sea Foam or something like it to try and clean the valves?
 

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Since it seems you’ve eliminated everything else, rockauto has ac delco injectors for $76, I would get one, install it and see if that solves the problem in that cylinder.


YouTube video on injector replacement.


After reviewing part of the video I think I would do all three injectors. I replaced an injector on my brothers C Class Mercedes and it wasn’t this involved. Mercedes has known injector problems also and the dealers like to replace them all and charge a huge premium price for being a Mercedes of course. New Mercedes Bosch injectors are $100, the dealer charges $600 each and does all 8 plus labor.

3x76=$228. Review the entire video, I saw at least one tool you would need to buy, most people don’t have a 27mm socket laying around. Get everything you would need, gaskets, O rings, tools etc and tackle it.
 

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It may always be a valve sticking/ not closing properly. Sea Foam is up to you, I have heard of mixed results. Easy thing to try.
Always use Top Tier Fuel and run a bottle of Tectron Concentrate every oil change. My opinion is that there are usually less lubrication issues and less carbon buildup on the valves when using synthetic oil and changing no more than 5K intervals.
Some folks have had good success with the CRC valve leaner spraying directly into manifold with cover off and vacuuming out excess, with valve closed of course.
 

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I’m not a mechanic but I did replace the coils and plugs on my 2009 when I had it to fix my misfires. I did not do or have the timing chain done. I has it diagnosed at a dealership before I did this and was told only use AC Delco iridium plugs. They said the electrical system requires a specific voltage (?) and other plugs can throw it off. AC Delco is the only way to go for these engines.
 
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