Flashing SES light random missfire
 

I get a flashing ses light when I hold my truck above 3k for a little while. If I drive like normal it doesn't do it. I changed my muffler last week to a flow with turndowns, could it cause it to think its missing. I can neither drive it nor here it missing. I logged it today and it shows #2 & #3 missing quite a bit and just a few on #4 & #5. I'm gonna check plug wires tonight or on the morning they are less than a month old and I'm pretty sure there all on good. Any ideas guys it still runs just fine I was just playing around lastnight and made the light start flashing now its bugging me

Did by chance happen after u filled up? had this problem before and ended up being injectors. but ya never know!!

no o2 sensor codes? did you do welding on the muffler? hurt any wires to the sensors or plug wires? misfires all over the bank 1 AND 2 spectrumis a whole system problem not just a cylinder or one bank problem. Make sure those o2's are in good condition and operating as they should. Sounds like you are lean, real lean, like misfire lean above 3K. Or like mentioned above, crap gas. Almost always, any exhaust work done and then misfires later is an o2 issue by damage to some extent.

Since you can log, what are the o2's millivolt at 2000rpm vs 3000rpm (constant throttle)? Just curious if it is leaning out as you go up in RPM or it's just straight lean and the misfires as it get more load.

Muffler was welded on and 02 sensors are new about a month ago when I did the swap and the back 2 are turned off. I will fill up tonight just make sure its not bad gas but I always by from the same place and 93 octane. Also shouldn't I be able to feel a miss like its saying it is?

It won't do it unless you hold it ready say around 3 grand. It will make it flash then if you shift it goes away or let out. You can go dead stop to wide open and it never makes it come on. Driving normal it never comes on either. Never had a miss I couldn't feel or here

How old are your serpentine belts?

Not real sure they were on the engine when I pulled it out of the truck, I reused them for the time being because they looked fine. Why do you ask?

Also I logged it on the way home last night. I can get it to say its missing between 2200 and 3000 if you hold a steady RPM. It can be missing and the get in it and turn more rpm and it goes away I would think if it was from being lean it would get leaner. I never once could feel it miss last night though. The volts on the o2's and they averaged 470-490 from 2-2800 constant throttle while it was detecting a miss mainly in cylinder #2 and #3. I'm still grenn to tuning what should the o2's be showing there?

I asked about the belts because the PCM detects misfires by monitoring the acceleration and deceleration of the crankshaft. If your belts are glazed they can start slipping and catching causing the crankshaft to speed up and slow down irregularly registering a misfire.

Well I was gonna replace the belts anyways so I may do that this weekend. Anything is worth a shot because its got me confused.

WTF is a spectrumis? I was hitting the rum when I posted this. Sorry about any nonsense that spewed.

When I say o2 damage I mean all of it. A wire anywhere in the circuit of the o2's. Yes, it's very possible to get misfires without feeling them, but if you have a cam your settings for misfire may be set too high (too sensitive) as well. Can you post your tune?