Sputtering/misfiring below 2500rpm

[Godless]

2006 GT manual, 210k miles. I'm having an issue, mostly once the engine is warm, where I have a misfire/sputtering below about 2500-3000 rpms. No codes. Once the car gets hot, if I drive it for about an hour, it will hard start.
I installed a new fuel pump. Upgraded said fuel pump. New throttle body. Tested all fuel related relays and checked all of the fuses. New fuel filter installed last year. New intake manifold gaskets, new used low mile IMRC unit.
When the car is cold or just coming to temp it tends to act completely fine. All of the horses, all of the torque. The warmer the car gets, the worse it behaves, to the point the car will try to die while leaving from a stop light, and it will noticeably miss when blipping the throttle in neutral.
Sometimes I see an improvement when I run seafoam through the gas tank, but that's always felt like a band-aid and after throwing this much injector cleaner at it you'd figure they would either be clean by now, or stop working entirely.
I've been told it could be a bad MAF, I've read fuel pressure sensor. I could throw $600 at sensors and not fix the issue so I'm looking for some insight. Thanks in advance!

 

[Noobz347]

No codes.

I have to clarify: What do you mean by no codes? You should at minimum, have a [separator code] and an [all clear] code. The lack of a check-engine light does not mean there are no codes.


If the MAF is bad or going bad, you should have a latent code for MAF out of range.

You are correct not throwing parts at sensors. If a sensor is bad, you should have a code for it.


My currently unsupported guess is that you have a ground somewhere that's causing gremlins when it gets hot.
My second unsupported guess is that the EEC itself may have issues.


We need a list of [all] codes including the separator codes.

 

[Godless]

I plugged a code reader into the OBDII port and it said there weren't any stored codes. I can see if the guys at work have a more advanced code reader they can help me use.

I've read that a maf can run an engine lean without throwing codes or a cel, but I would imagine that's fairly uncommon.

I'm going to inspect plug wires once it gets dark and look for any arcing, I have also seen that discussed in older threads.

I would imagine a scanner might be able to run a test on the EEC as well? Apologies for any dumb questions or ideas. Definitely not a mechanic.

 

[Noobz347]

If you plan to try and diagnose and repair this yourself then yeah... You're going to need a decent reader.


Some suggestions (there are others as well):

Zurich ZR11S OBD2 Code Reader with ABS & SRS – Great mid-range tool. Reads/clears engine, ABS, and SRS codes. Good display.

Innova SD35 Tablet‑Style Diagnostic Scanner – Big screen, lots of extra features (service resets, etc.). More expensive but powerful.

Foxwell NT301 Live Data Reader – Excellent value. Live data display, freeze frame, readiness tests. Solid “step up from basic reader.”

GearWrench GWSMARTBT Pro Bi‑Directional – You can do bi-directional tests, which can help diagnosing certain modules.

 

[Godless]

If you plan to try and diagnose and repair this yourself then yeah... You're going to need a decent reader.

Fortunately, I work at an offroad shop. The techs don't specialize in diag and repair, they're mostly doing custom fab and fitment, but they have scan tools and would probably give me a hand. I'll poke around tomorrow and see if we can get any good data.

 

[gkomo]

What noobz is saying, like on Foxes if your car is running perfect with no codes you would still get KOEO code 11, then code 10 to say its ready for KOER where you would again get code 11 if everything is running how it should, just as an example. Yours may 3 digit codes.