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DAM fluctuation quite a bit after new Ignition coils

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I've been trying to read though as much information as I can on understanding my datalogs and DAM but just not having any luck trying to figure out what is going on with my 2011 LGT. If anyone can help me interpret my logs it would be greatly appreciated.


I just had new ignition coils put on and ever since the DAM can go from 1 all the way down to .125 then work its way back up to about .812. I was running stage 2 91, now I'm back on stage 1 91, no real change. I'm going to try stock tune tonight. The car runs much smoother with the new ignition coils despite the constantly changing DAM. What promoted it is the 2nd cylinder coil died. All the coils looked quite beat up from winters in upstate NY so figured best to just replace them all.


I've had quite a bit of work done on my car the last year, so some information on everything, it may get long, sorry. My car has about 137k miles. Till the last year have never had any real problems. I have a invidia catted down pipe, Borla exhaust and K/N air filter. I have been running stage 2 93 for quite a few years. Just bumped it down in May to 91 since I was out of town and to many gas stations only have 91.


Dec 2018 I had the head gasket done, new radiator, hoses, timing belt and clutch. After the work I noticed the car had more power but would I guess you could say stutter a little when pulling hard in 3rd or 4th gear and boost was over 13 psi. It didn't always happen but was repeatable enough if you pushed the car hard. Based on my research it seemed like the fuel pump wasn't keeping up as nothing really showed up odd in the datalogs. I had the local shop check it and they said the same thing my fuel pump wasn't keeping up to just dial back my tune a bit.


4th of July weekend suddenly I got a check engine and a cylinder 2 missfire message. Figured it was the ignition coil. Sadly I did have to drive the car on 3 cylinders to the shop.

Right after having the new coils put on I noticed the stutter that was there was gone, it pulled hard now right up to about 16.8 PSI nice and smooth. I plugged in my AP and started logging. That is when I noticed the DAM dropping a lot, if I did a harder pull at times it would go back to 1 or close. Not always. So now I'm watching it non stop. It goes up and down, mornings it seems to be better, could it be the cooler temps? My drive to work is about 40 miles mostly 55-65 mph.


I attached my datalog from the drive in this morning. I didn't really drive hard at any point. I had just put in the stage 1 91 map so the CPU was cleared. My car always starts with the DAM at .812, in the past it would just work its way up to 1 and stay there. Now it worked up to 1, the started dropping all the way down to .5.

Am I data logging all the right things? I'm not really sure what to even look for to try and fix.


Thank you so much for any insight that can be offered.


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You seem to be having quite a few knocks on Cly4. The count just continues up and up.

I would suggested to recheck your plugs, ensure the gap is between “0.027-0.030”.

Do the “spring stretch” on the coil packs.

And while your at it, toss in a can of fuel injection cleaner in the tank.


Looks like the main focus is cyl 4 at this point. There is a small vacuum source above cyl 4 for the fuel pressure regulator. Verify that isn’t cracked or damaged.



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Thanks for taking the time to look the log over, I noticed that as well with cylinder 4, just wasn't sure really what to check with it or it that was the only issue.


Spark plugs are 6 months old, changed them at the same time as head gasket, I put in NKG SILFR6A plugs. But I'll double check them definitely could have had a bad one.

Data logged on my way home and tried to push the car some, was able at one time to get it up to 6000 RPM in 3rd. Surprise driving more aggressively and the DAM went up to .938-1. Cylinder 4 still shows more Knock sum however.


What causes the DAM to improve when you drive more aggressively (turbo has positive boost more even if only a few PSI)


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I would try moving your #4 coil. For your 91 OTS MAP, I would make sure its the 91 MAP, not the ACN 91 which is meant for the gasoline of Arizona, CA, Nevada.


If that doesn't work, I would add some octane booster, to determine if the knock is due to octane.

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Yes I put in OEM coil packs and SKG SILFR6A spark plugs, they appeared to be identical to the OEM ones from what I could see. This week I will check the spark plug gap in cylinder 4, then swap the coil pack and spark plug to a different cylinder. If the problem moves then I just need to determine if it is the spark plug or coil pack.


Hopefully pick up some injection cleaner tomorrow as well.


I always run 93 octane fuel just running the stage 1 91 map to be safe for now.


Why when I just drive in a lower gear than I normally would for the given speed do I find the DAM getting a little better. If I cruise in say 6th gear on the thruway it drops. If I accelerate harder often the DAM will go up to 1 or close.


Anything else I should consider?

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  • 2 weeks later...

Finally got to moving the spark plug and coil pack from cylinder 4. The spark plug gap was .025" increased it to .027", since the NGJ plugs have a spec of .027"-.030". Plus moved the plug to cylinder 2. No change I'm still seeing the cylinder 4 knock sum increase quite a bit.


I often notice the Fine Knock learn will reduce the timing even when the feedback knock has remained 0 for a long time. Some times as much as -5 degrees. Often this coincides with cylinder 4's knock sum being incremented yet no feedback knock.


Anyone have any other idea's as to what could be going on? I'm at a loss as to what I should check.


I did find some older data logs from February, I noticed even then cylinder 4's knock sum was much higher than any other cylinder, but the DAM stayed at 1.

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