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Discussion Starter #1 (Edited)
Hey guys,

It's a 2011 cts4 with the 3.6, 85kish miles on it. Trying to troubleshoot a cylinder 1 misfire. It's thrown a few codes for random misfires as well as cylinder 1 misfire, this Weekend I swapped the original spark plugs out for new ones (autolite 5263), as well as did an oil/filter change.

Started the car up and still a noticeable misfire at idle, plugged the scanner in and it's cylinder 1 again with a few on cylinder 2. Tried swapping the cyl 1 & 2nd coils with no changes. Any advice or help?

 

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You're on the right track. But you should swap the coils from a cylinder that isn't throwing codes. Then if the code changes to the one you swapped from, you know it's the coil is bad.

Marv
 

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Yes, first swap with a cylinder giving no misfires. For me, after new plugs and all new coil packs, it ended up fuel system treatment did the trick.
 

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Discussion Starter #4
Sorry for the typo, was posting from phone, it's a 2011 cts4. I'm going to try swapping for a completely different cylinder/a new coil pack. Next up is seafoam or some other cleaner. No combustion cleaning has ever been done on the car so I'm wondering if it's a lot of carbon build up due to DI.

Here's a pic of the misfire counts, after changing coils 1 & 2 the counts remained the same with cylinder 1 pegging 255+ and cylinder 2 hovering around 50-60.

Any recommended fuel sys cleaners?

 

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I don't think in-gas cleaners will work because it's DI. There are some posts here regarding putting seafoam into the intake via a vacuum line, but I don't have any knowledge of that. I would try another coil pack foam a cylinder say, 3-6 that isn't misfiring, first.
 

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To clean carbon out it has to be done manually.
 

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I have done seafoam and GDI intake cleaners. My misfires and reduction in responsiveness remained an issue. I then used gumout regane high mileage fuel system cleaner and it made a vast improvement. Yes, it's a DI engine and yes I was skeptical about it. Yet, there might have been some fuel like deposits etc that the cleaner fixed.
 

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Discussion Starter #9
Well new plug and coil made zero difference.

you just poured it in the tank or you went through a vac line on the manifold?


I have done seafoam and GDI intake cleaners. My misfires and reduction in responsiveness remained an issue. I then used gumout regane high mileage fuel system cleaner and it made a vast improvement. Yes, it's a DI engine and yes I was skeptical about it. Yet, there might have been some fuel like deposits etc that the cleaner fixed.
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Well new plug and coil made zero difference.

you just poured it in the tank or you went through a vac line on the manifold?


I have done seafoam and GDI intake cleaners. My misfires and reduction in responsiveness remained an issue. I then used gumout regane high mileage fuel system cleaner and it made a vast improvement. Yes, it's a DI engine and yes I was skeptical about it. Yet, there might have been some fuel like deposits etc that the cleaner fixed.
 

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It just goes in the tank when nearly empty, then you fill it up. Just follow the directions on the bottle.
 

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Discussion Starter #12
From what I have read, the only/best way to really clean out carbon deposits on our DI engines is to mechanically clean them. I have seen pictures where they have gone in and NOT pulled the heads to clean. I don't know how, but it is documented somewhere on this forum.


Here it is: http://www.cadillacforums.com/forums/2008-2013-cadillac-cts-general-discussion/414745-3-0-3-6-intake-valve.html
Thanks for the link. New plugs, on that cylinder, new coil, seafoam through manifold, and GDI in tank, and went and did some "italian tuneup" driving. Little bit better but still there. CEL is cyl 1 misfire and occasional random misfire. During the drive was logging and any sort of throttle resulted in Knock retard readings of 6*+ up to 10.5* KR at hard throttle.

Going to grab an oem set of spark plugs, double check gap on them (need .040 from what i've read) and change out the front o2s this weekend. (wouldn't be the first time i've seen bad o2s cause a misfire, and either way they have 85k on them so it won't hurt.)

After that next step is pull manifold to clean the valves by hand. Probably next weekend since have customer cars to take care of this weekend.

If all fails after that looks like head is coming off to replace that injector.
 
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