Ok… so… 2000 trans am, long tube headers, corvette intake, high ratio rockers, hardened pushrods, cam, AIR and EGR delete, stock ignition, cats , SLP loudmouth exhaust, computer tune, double roller timing chain, ported and polished throttle body, might be a larger MAS (don’t remember!)
So the SES light has been on forever due to rich bank 2 and I’ve never been able to solve it but she was running fine until a couple weeks ago. The SES light began flashing and she felt like she had a miss. Internet says the flashing SES light means misfire and that’s what I feel is happening. Starts flashing under acceleration but goes away at lower RPM but stays flashing when engine warms up (for the most part). Hard acceleration feels like it’s missing. And exhaust smells richer than it should. Code reader first gave me P0135 and P0155 which indicates O2 bank 2 sensor 1. But these could have been old codes because the lights always on. Resetting the SES light (since she’s had a history of the light being on) clears the codes but the light still flashes as above. Was hoping to see something else after a few runs to help diagnose. Only other code was a P1153 which again is O2 insufficient switching bank 2 sensor 1. I went ahead and changed the O2 sensor anyway but didn’t expect it to help the miss. But no new codes have been set with about 4 runs on the car.
I know I used a tuning tool back when I was building her but can't find my info in what tool I used. LS1Edit or LS1 something.... Last I remember it wasn't working anymore anyway and not supported by the vendor.
So I'm not understanding why I'm seeing the flashing SES light indicating a miss or multi misses but I'm not throwing any codes??
Someone has suggested a clogged cat so I guess I'll take the Y pipe off to check.
So now riddling it’s out I’m thinking plugs and wires replace (can’t hurt… she’s given me literally 100k miles on the ones I used when building) and possibly one coil and start swapping them out until I find a bad one?? I never upgraded the ignition so might even be a good idea to just go ahead and get the MSD coils and replace them all but some reading here suggests truck coils or stock are just as good or better. Also saw a YouTube video where the issue turned out being a broken valve spring but I'm not seeing or hearing what that gent saw.
Any thoughts?

 

i had a similar issue - bogging, sputtering and occasional flashing SES. but only under heavy load. I ended up having a 2 cracked coils and a cracked spark plug. no codes. replaced nd issue was resolved.

 

Yeah, I would change the plugs or at least look at them. And check out the coils too. It is odd that you haven't got a misfire code for a particular cylinder or two.

 

that’s what I was thinking. No codes, flashing light…. Kept making runs to maybe see a code but all I’ve seen is that bank 2 LTtrim hovered around 12 and bank 1 at 0. Not sure what this might mean if anything.
And O2S21 seems to indicate a much higher output than O2S11 but switching is within bounds now.

 

I’m gonna order plugs, wires and coils. Pretty well accepted it’s time to freshen her up. Mine flashes under moderate acceleration or even light if I just let the revs build and hold it at say 2k for a bit longer than someone would when running a manual trans.

 

I suspect your misfire is initially due to faulty O2 sensors, which is why you never got any codes indicating a specific cylinder. But since you've driven it for a while like this, some of plugs and fuel injectors could've been subsequently fowled by carbon/oil buildup, which you're addressing now. If you can get around to replacing the O2 sensors, that would be best, since it could all happen again.

I had random misfires/hesitation when my O2 sensors were damaged for several weeks and even continued to have residual misfires after changing out the O2 sensors due to buildup in the cylinders. I know this was the case because I got the P0300 (random misfires) code. It took months of driving and using upper cylinder cleaning agents to fix it completely although a complete plugs + injector swap would've been an immediate fix.

As long as you don't get a code indicating a problem within a specific cylinder such as P0305 (cylinder #5), it should be safe to assume the issue is in the air/fuel controller.

 

What I’ve found so far….
First let me say mine is the car that time forgot. Or better yet,… I forgot. She always just ran and so through various life happenings I have neglected her.
I was looking through my old documentation and find quite possibily the plugs have not been changed since installed with the cam swap in 05/06! And they are regular T55’s and not the iridium.
No wonder she’s giving me trouble.
To that length it seems the plugs weren’t the problem. I found #5 spark plug wire was rusted and burned through at the plug boot. #8 coil pack is rubbing on something or vibrating against something. I suspect wireloom but will check today. The lest bolt in the coil pack frame up under the passenger side was not installed. Might be why it was rubbing but the bracket is pretty stout so it’s probably wireloom. I don’t think the coil went bad but I’ll find out soon enough.
pulled the valve covers since I was there and no damage underneath as far as I can tell. Decided to freshen up the exterior of the motor (since I’m there!) and crinklecoated the covers. I had polished them to a pretty good shine back when but time has takes it’s toll. I’ve learned (again!) you can’t just drive her… need to maintain everything!
New EGR valve, new wires, new plugs, and all new O2 sensors (front ones anyway). The headers seem to have a lot of rust on them and it’s bothering me…. And I’m fighting the urge to just pull the motor and have a winter project.
I’ll report back when she’s together as to if this solved the issue. Too many threads go with the problem and then people’s solutions and then you never know what the outcome was.
Thanks for all the thoughts and reply’s!

ok…. My app isn’t showing The whole write up to edit so I’ll just add this….
where I said the plugs weren’t the problem … I went to some videos to refresh what I know about reading a plug. Apparently I didn’t remember enough.
the straps were brownish to somewhat blacker on several cylinders. The electrodes were all still there (as were the straps) but the gaps were the old norm of .055 to .060 and were varied between all 8. Additionally they were black as was the porcelain. I believe I was running rich which might explain the O2sensor difficulties I was having.
But not changing or checking these plugs for so many miles kinda negates reading them for a good overall analysis I believe.
I’m leaving the ACDelco iridium plugs I was able to find at the factory recommended gap of .040 and will pull them after some miles to get a better read. So the plugs were probably contributing to my issues.
Just waiting for new plug wires.

 

Resolved!
ended up being the wires and plugs. I got away cheap!
I replaced the forward cats too since I got a good deal on them.

 

I did not read all the responses, so I hope what I say was not mentioned above, I am not an expert in anything automotive, and a flashing SES light on our vehicles means "multiple misfires". Hope this helps out in some way.

 

see the last response before yours. I found it 😊
but thanks for the input!