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Let me know if I'm not in the right spot here. I've got a '13 SS. Cam, long tubes, bolt ons. The car backfires from time to time downshifting, but it's never been real bad. Yesterday, backfired at 20mph shifting from 3rd to 2nd, and was audibly different from the typical backfires. An immediate power loss followed. Looking for direction here. I've pulled the high flow cats...the inside of both look perfect. I've pulled a few plugs....number 3 was black, the rest I pulled were silver. Any advice going forward here?
Disclaimer: Car has MSD ignition coils. I know they're ****, but were on the car when I bought it. And it got me thinking...maybe the coil going bad caused the backfire and is the problem instead of the backfire. Does it sound legit to anyone out there, or am I pissing in the wind?
Last edited by 02SS:ZEUS; Sep 30, 2018 at 06:16 PM.
Once you've gone over all the basics, or trouble-shot with a stock coil pack possibly, I would consider doing a compression test to check the health of the cylinders.
Silly question maybe, but did your SES light ever turn on?
Edit:
How long have you had the Cam/mods?
How many miles are on the engine?
Did you happen to get an AFR print out of the tune?
Does your engine idle as usual?
Edit # 2 (Obviously I suck at putting all my thoughts on the original post I make)
Purchase a stock/replacement coil/pack from Autozone
Purchase stock wire set
Purchase all spark plugs
You're going to use these just for the purpose of trouble-shooting the ignition. If the problem persists, at least you know it's no longer electrical, and perhaps a mechanical problem. You can always just return those items, well, maybe not the plugs.
Maybe you broke a valve spring or some kind of cam/lifter/rocker arm situation. Maybe buy a single coil and replace the number 3. If not maybe pull a valve cover see what's going on.
Another cause could be an over stretched power band.
ok seriously though, yeah make sure sure the ignition system is healthy. Then inspect valve springs and I would do the compression test for my own peace of mind.
If it backfired out the intake (zeroing I. On audibly different backfire) then you either somehow lost your timing going down the road or lost control of a valve or valves.
If you are luck it just a spring. If not lucky, possibly bent valves. If RRALLY not lucky, timing chain may have jumped a link. It has happened to me before.
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Power loss after backfire 
