Picked up my third FBODY and having a weird issue...

56k mile 2000 SS M6 1SC 1SZ very clean car with a whisper lid and a Borla catback

Plugs replaced with TR55 @ .050"
Wires replaced with Taylor 10.5 409
MAF cleaned three times
PCM reset
IAT cleaned/K&N cleaned
Fresh fluid swap
Fresh slave cylinder
Fresh 93 good gas ran through it 3x tanks
Seafoam in the tank (full can)
Seafoam in the brake booster (full can and TONS of white smoke)
Fresh tensioner for AC and Serpentine
Fresh idler pullies
Fresh fuel filter
Fuel pressure is at 55-56PSI at idle

My car pulls hard to 5k and then starts missing and stumbling and making a rattling marbles/rocks in a can noise coming from the driver side. I am running out of ideas here and not sure what I should do next...The car pulls fine every where else and makes no weird noises.

 

What is the fuel pressure when it starts pinging?

 

I haven't been able to log that...currently installing a FPA-001B to cure any fueling issues up top. Currently trying to get a local person to let me borrow their HPT cause I can only log and view basic PIDs with my OBDwiz

 

The car sat for around 6-8 years and only has 4k miles in the past 14 years by the way

 

Look at the valve springs.

 

^^^^ Do this ^^^^, but also, is the gas in the tank still the old gas that's many years old? If so, there's the problem. Put some fresh gas in it!

 

I was thinking valve springs....what is the best way to do that? Valve covers off?

Good gas has been ran through the car for 3x tanks to eliminate that

 

Kinda tough to check them with the covers on,,,, first remove covers, check for broken springs, and if there are none, remove the springs and check them for pressure.
Besides all that, the fuel filter(s) might be full of crud the fresh gas would have rinsed out of the tank. Unless it's been done, put in new fuel filter(s).

 

ah okay thank you for helping me better understand, would a compression / leak down be a good idea first?

 

Can't hurt at all. Do that first.

 

 

 

Screens in the fuel injectors may be clogged. What do the fuel trims look like at moderate throttle? I just had some trouble with number 8 injector, All the crap tends to collect at that last injector. Mine was acting up in the 4-5k range missing and surging. Fuels trims on bank 2 were high at times and when I pulled the spark plug on number 8 it was much whiter than the others. The screen was partially blocked.

 

Also if it sat for years without being turned over REPLACE ALL THE VALVE SPRINGS, trust me some are poop.

 

Your symptoms sound like valve float

Also, not good for valve springs to sit for years compressed, so I wouldn't be surprised if you have several that are weak

 

 

You gotta drive it at light to moderate throttle watch the fuel trims. Will give you some idea what may be going on. Could try Lucas fuel treatment in small amounts to start off with, it really cleans but if you put in a full treatment all at once you may make more trouble by moving too much crap all at one time. I'd try half what they recommend for a few tank fulls and watch the fuel trims. As far as the valve springs its time to change them, too old and some are weak from sitting compressed for so long. Who knows some may be cracked. Pull the valve cover and carefully inspect them. Use a ratchet and socket on the crank bolt to rotate the crank so you can inspect all the springs open and closed. Even if they check ok change them. Good Luck

 

Might want to check knock sensors they will pull timing at high RPM if they are defective or are really seeing knock. Water can get in around them and really make a mess,,,

 

thanks everyone! i already ran a bottle of lucas fuel injector cleaner split between two tanks and then a tank of seafoam to finish it off. my buddy needs to change his springs too so we plan on tackling this. i plan on getting the tank back in the car and pulling some valve covers this weekend

 

i've posted before stock springs over 5k rpm can sputter / flutter. my car did it with only 48k milage when i purchased and i've seen multiple cars do it on dyno day. after i added ls6 springs no issues anymore.