When engine warm, turns over awhile before starts. Fine when cold. Chevy garage unable to find problem. 100,000+ miles. They replaced fuel pump 2 months ago. Still happens.

One possible reason for this could be a faulty engine coolant temperature (ECT) sensor. The ECT sensor tells the engine control module (ECM) the temperature of the engine coolant, which is used to adjust the air/fuel mixture for starting. If the ECT sensor is faulty, it may be sending incorrect temperature readings to the ECM, causing the engine to not start in cold weather.

Another possibility could be a weak fuel pump check valve. When the fuel pump check valve fails, it can cause the fuel pressure to drop when the engine is turned off, which can cause hard starting in cold weather .

It's also possible that the battery is weak and not providing enough power to start the engine in cold weather. Cold temperatures can reduce the battery's cranking power, which can make it difficult to start the engine.

I would recommend taking your vehicle to a certified mechanic to diagnose the issue.

Have you replaced the coil?

Depending on how cold you are talking, it could be water in your fuel system freezing and blocking the fuel delivery, do you know if you are getting fuel to the engine when this problem occurs?
You can try a fuel conditioner one that removes water from the fuel system but is safe for injectors and see if that helps.

Have you checked the fuel pressure regulator to see if its leaking?

I’m happy to assist further over the phone at https://www.6ya.com/expert/jeremy_d728a59f986299fa

fuel system might be losing pressure somewhere,or could be fuel pump,have a fuel pump pressure test done,that should tell you

Hi, Sounds like your fuel pump is on it way out. If you have over 100,000 miles, change it.

Try replacing the fuel filter also Has it had a tune up? they need to have the plugs replaced at 100,000 if the fuel filter does not work then the most probable cause is the fuel pump is losing pressure when hot. The pump warms up and the check valve fails to close all the way allowing a now fuel or fuel starvation.

I didnt see it in your list, so I would suggest the O2 sensor, usally found on the exhuast pipe near the engine or on the back of the engine

THIS PROBLEM IS ALMOST ALWAYS DUE TO A FAILED FUEL PUMP PRESSURE CHECK VALVE, REPLACE THE FUEL PUMP.

THE FUEL PUMP IS LOCATED IN THE FUEL TANK. IF IT IS WORKING YOU WILL BE ABLE TO HEAR IT SQUEALING WHEN THE KEY IS TURNED TO THE RUN POSITION PRIOR TO ACTUALLY STARTING THE VEHICLE. IT WILL BE A HIGH PITCH. IF NOT THEN THAT WOULD BE A STARTING POINT. ALSO FUEL INJECTED CARS HAVE A COLD START ENRICHMENT VALVE THAT COULD BE THE PROBLEM. THIS VALVE CAUSES A MOMENTARY FUEL RICH SITUATION SO THE ENGINE CAN START. IT IS BASICALLY A CHOKE FOR FUEL INJECTED ENGINES.