1F4STSS

Hey everyone! First post but been lurking for a long time, from South Dakota. I have a 2005 Silverado SS AWD with 93,400 miles. Truck was a salvage vehicle, hit on driver side between rear door and box, I bought it after it had been rebuilt, looked like they did a good job and I can't complain about anything so far, I've had it for about 12,000 miles, it's my DD. As far as upgrades, last winter I put in a Comp Cams XR275HR stick, 222/224 @ .050 duration, .566/.568 lift and 112° lobe separation. Went with LS6 springs thinking the blue ones were the right ones, evidently they weren't as they're rated for only .570 lift. So now I've got Comp Cams 918 springs good up to .625 lift and chromemoly pushrods. The intake is completely redone, I put on a Holley mid-rise single plane spider manifold, Holley 105 mm inlet elbow with a 4 barrel isolator plate, still using the factory throttle body with an adapter, and a K&N plastic intake tube fed by a pretty big Green Filter high flow air filter. Holley fuel rails, it's a returnless fuel system with factory injectors, MSD 8.5 mm Super Conductor plug wires, and NGK TR55IX plugs. The exhaust is still factory manifolds (LTs are the next upgrade) with cats, it's true dual through a Magnaflow X pipe and 2 Dynomax 12x4 inch race bullets and dumped before the axle. It's also Black Bear AutoCal tuned for 91 octane.

So on to the issue, a couple months ago I was talking with Justin over at Black Bear trying to figure out a ping, I ended up sending him a log exhibiting the ping when he noticed I had either a misfire or exhaust leak, so my focus switched to figuring that out. I believe this was back towards the beginning of July, and I've been hunting ever since. I did notice what I thought was a miss at cruising speeds prior to him mentioning it and he confirmed that. What I've determined about the nature of the miss through monitoring data on my AutoCal is, it only occurs during part throttle under NO load and seems to be primarily on Cylinder 5, although 3, 4, and 6 also experience it, 6 being the second worst, and 3 and 4 rarely see any. So far I've tried moving plug wires, plugs, coil packs, and injectors to different cylinders on both banks to see if the miss moves too, but it doesn't. If I sit in park and throttle it to about 1300 up to 3000 RPMs Cylinder 5 will miss up to 150 times before hitting, depending on the amount of throttle given, more throttle = more missing, Cylinder 6 will miss up to 40 times. Those numbers are based on EFILive software watching the MFCYL counters. At cruising the miss isn't as bad, going up to about 30 on Cylinder 5, but I never get a single miss while under load if I'm accelerating or at WOT. I have used Seafoam in the gas tank, and Seafoam spray right through the throttle body, none of the springs are weak or broken and the stem seals look good, pushrods are all straight too. I've cleaned up the grounds as well. I don't believe there are any vacuum leaks and I don't hear an exhaust leak anywhere. I'm not sure where to look next, it seems the misses only occur in the second rotation of the engine as 1, 2, 7, and 8 never ever miss, which led Black Bear to believe it was a PCM issue, which is why I cleaned grounds and switched the PCM to my old one and flashed the newest tune to it. No dice. At this point I'm lost. I will do a compression test tonight after work to see if I need to dig deeper into the engine but hoping to get some ideas from you geniuses until then. Any ideas, advice, and/or help is greatly appreciated.

Sorry for the long post. Thank you!

trxmxzx

iTrader: (7)

Injectors?

1F4STSS

Checked injectors, swapped from #5 to a known good cylinder, swapped from #6 to a known good cylinder, checked voltage and resistance last night, that was all good, and did a compression test last night. Everything checked out. But the miss continues. Is it possible my fuel filter could need changing? I'm not sure if that would cause this problem.

Toes

iTrader: (1)

Sounds more tune related. Are you getting your tune done remotely? Or just loading in tunes? But I would think your timing or fuel needs to be adjusted in that area.

1F4STSS

Yes I'm currently getting tuned remotely, I use my AutoCal to datalog the truck while I'm driving, then email the log to Black Bear, they look at the log and build a tune accordingly, they then email the tune to me and I flash it to my PCM via my AutoCal. This is followed by another datalog to ensure the new tune is working correctly. It would be hard for me to believe it's a tuning issue just because I know Justin at Black Bear is very good, especially with the Silverado SS trucks, but I suppose it is possible. I've been working closely with him in trying to track down the problem and have sent him a few datalogs exhibiting the miss. One thing was brought up today while exchanging emails with Justin regarding the timing and possible sprocket misalignment, I wondered if maybe my timing chain is stretched. I'm still using the factory timing set and when I put in the camshaft it did seem pretty sloppy. Could the timing chain being stretched cause this sort of problem? I intend to put a double roller on very soon regardless.