Runs great for 10 to 15 minutes then loses power. Cools down runs great again,.

2004 Saturn L300 version 1 sedan, 2.2. 4-cylinder, about 160K miles

Started cold the car runs absolutely great for about 15 minutes (until it gets warm) then it has almost no power and must cool down and when cool again runs great again for 15 minutes or so...over and over again. It moves out very slow from stop regardless of how much gas pedal it gets. Sounds like it's bogging down...too much fuel in the mix...timing off...

When running OK, fuel trims are around zero to 3 and the short term is ranging a little but stays within 5,
the downstream O2 sensor is ranging, the upstream is new and is ranging from around 0.1 to 0.9 and
fuel is in closed-loop.

Before the car begins running rough, I can hear a slight change in the rpm when at idle and the tach shows a drop from 770 at idle to about 730.
Also, before the car begins running rough when pulling out the car surges ever so little.
When the car starts running roughly the short- and long-term fuel trims are positive up around 15.
I don't drive far as I am aware, I have a problem and I drive only to test, but if I do have to drive more than a mile to get back after the car begins running rough, the cat converter gets real hot, about 750 degrees. Otherwise the cat does not get so hot. And the cat is brand new, first used today and like the old one, it gets hot when the engine continues to run when running rough.

I don't believe this is an evap problem. I also can't detect any misfires. I have had many DTC's over the six months I have worked on this and have thrown a lot of parts at it. The only DTC I get now is "inefficient Cat". The DTC's in the past have been for misfire and evap leak. I have not had any other DTC in months. I get the feeling that the upstream O2 sensor is being ignored by the ECM.

Parts thrown: Vent solenoid, purge solenoid, coolant temp sensor, map sensor, thermostat, ignition control module, fuel pressure regulator, fuel filter, crankshaft position sensor, I have tested the battery and alternator, replaced the screens on and cleaned the fuel injectors, new intake manifold gasket, new throttle body gasket, I have a smoker and have tested repeatedly for evap leaks and cannot find any.

Any help would be appreciated.

Have you checked for an exhaust restriction? Remove front o2 sensor install back pressure gauge drive until it acts up gauge should read 1 psi or below. Also can you check fuel pressure when it’s in the no power situation? Should be easy as I think those have a schrader valve on the rail.

Was the old CAT blown to the point that it rattled? Pieces of the old CAT can get lodged in the muffler and piping after the CAT causing a low power condition. The CAT temp should be around 600 degrees to work properly. A P0420 inefficient CAT is just that, a bad CAT. Probably an aftermarket. As Cheryl commented, check for back pressure.

Engine runs good when cold as the 02's are in open loop and do not control fuel at this point. When the engine gets hot, the 02's go into closed loop and report to the PCM which controls fuel. High ST and LT of +15 in closed loop indicates that the engine is starving for fuel so the PCM is adding fuel to compensate. That's +30 overall trim. The PCM is probably close to throwing a code.

The one thing you did not do was check for fuel pressure. You changed the regulator, but it sounds like the pump is weak. Pressure readings will tell.

A couple of thoughts come to mind.

1) Others have suggested checking the EBP, and while I agree that may be smart, I wonder does this vehicle have a pid for that? Also, why wouldn't an exhaust restriction cause problems in the first 15 minutes?
2) How quickly does the car move from open loop to closed loop during these first 15 minutes?
3) Do you have a scanner that allows you do save data? If so, you might store some data and watch for what changes as the trouble begins.
4) 15 minutes is a pretty long warm up cycle. I'm wondering if this is oil temp related. Does the car use VVT with phasers?

Start collecting/logging PIDs, using torque pro if nothing else. Watch fuel trims, EOT, ECT, CylinderHead temp. Oil Pressure of PID exists, Voltage of battery/main, valve timing if used, EGR if PIDs, MAF/MAP readings... I look forward to seeing more data (upload or paste-bin a csv file). Make notations about when the issue begins.

Yes, I have. There is no exhaust restriction. I just replaced the Cat converter and checked the exhaust and the BkPres too.
The fuel pressure is good and holds. The fuel pressure regulator and filter are new too.
Thanks

The old cat may not even be bad. I assumed an exhaust restriction caused by a bad cat, possibly I imagined the guts of the cat were swelling and blocking the exhaust. Brand new cat and the car did exactly the same thing. It is not the cat or a restriction and the fuel pressure is good and holds.
I think it is electrical, ECM or sensor related. Years ago I tore the wire to the Intake air temp sensor and the engine ran very rough, the fan went on high and the transmission shifted with a loud and easily felt clank. I repaired the wire and the problem disappeared.

Just cause the pressure holds on fuel pressure doesn’t mean it’s good under load. Are the oxygen sensors lean below 450 mv when it acts up?

I theorized the cat was damaged and when hot would block the exhaust, even though I found no one else on the internet reporting anything similar. I installed a new cat and got the same results. There is no exhaust restriction.

It takes only a few minutes to go into CLoop for the fuel.

I have OBDiz with professional ad on.

No VVT.

"Start collecting/logging PIDs, using torque pro if nothing else. Watch fuel trims, EOT, ECT, Cylinder Head temp. Oil Pressure of PID exists, Voltage of battery/main, valve timing if used, EGR if PIDs, MAF/MAP readings"...will do.

Thanks

Good to know.
I will drive and record and see.

Thanks

It might be worth running it till it starts to run rough then turn it off and remove and check the spark plugs to see whether it is a "global" problem or something happening in one cylinder.

Sounds like when it goes into closed loop is when the problem starts occurring. So it suggests a fuel control problem. High fuel trims suggest engine is running lean. Does this change when it is held at 2500 RPM? And is this a MAF or MAP engine?
I seen 02 data when you said it’s cold, how about when it’s hot? New 02 doesn’t mean it’s good, and was it OEM or aftermarket?

Have you ruled out exhaust or vacuum leaks?

(Also, are you using EOBD mode or manufacturer specific mode? I would suggest EOBD if you’re not already using it to rule out substituted values as it will show substituted values in manufacturer specific mode.

No, the engine runs bad many minutes after being in closed loop.
O2 sensors I need to record while engine is running badly.
I have checked for unmetered air and exhaust problems and can't find any.
MAP
Not familiar with EOBD. I have an OBD2 sanner.