Long start

Welcome to 2CarPros.

The first thing that comes to mind is that the engine coolant temperature sensor (ECT) is inaccurate. If you have a live data scanner, check the signal from the ECT. Is the temperature it is indicating close to the coolant temp in the engine?

If the sensor is telling the power-train control module it is -40°F and it's actually 80, the PCM will make the fuel mixture extremely rich to allow the engine to run at the cold temp, and basically flood the engine because it isn't actually that cold. And, the opposite can happen causing a mixture that is extremely lean. The idea that you have to press the accelerator leads me to believe it is related because when you depress the accelerator, it shuts fuel down at the injectors.

Let me know if you have a live data scanner and what you find.

Also, here are the directions for replacing the sensor if you find it is the problem. The attached pic correlates with the directions. Now please keep in mind that the number of miles on the engine may have an affect on engine compression. That too can cause a hard start, especially in cold conditions.

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2000 Pontiac Bonneville V6-3.8L VIN K
Engine Coolant Temperature (ECT) Sensor Replacement
Vehicle Power-train Management Sensors and Switches - Power-train Management Sensors and Switches - Computers and Control Systems Coolant Temperature Sensor/Switch (For Computer) Service and Repair Procedures Repair Instructions Engine Coolant Temperature (ECT) Sensor Replacement
NOTE: Use care when handling the coolant sensor. Damage to the coolant sensor will affect the operation of the fuel control system.

Pic 1

REMOVAL PROCEDURE

IMPORTANT: Care must be taken when handling the Engine Coolant Temperature (ECT) sensor. Damage to the sensor will affect the operation of the fuel injection system.

CAUTION: Refer to Battery Disconnect Caution in Service Precautions.

1. Disconnect the negative battery cable.
2. Drain the radiator coolant. Refer to Draining and Filling Cooling System in Cooling System.
3. Disconnect the electrical connector (1) from the ECT sensor (3).
4. Remove the ECT sensor shield (2) from around the sensor.
5. Remove the ECT sensor from the engine.

INSTALLATION PROCEDURE

IMPORTANT: Care must be taken when handling the engine coolant temperature sensor. Damage to the sensor will affect the operation of the fuel injection system.

NOTE: Refer to Component Tightening Notice in Service Precautions.

1. Hand-start the ECT sensor (3) into the engine.
2. Tighten the ECT sensor.

Tighten
Tighten the sensor to 25 N.M (18 lb ft).

3. Install the ECT sensor shield (2) around the ECT sensor.
4. Connect the electrical connector (1) to the ECT sensor (3).
5. Refill the radiator with coolant. Refer to Draining and Filling Cooling System in Cooling System.
6. Connect the negative battery cable.
7. Start the engine.
8. Check for coolant leaks
9. Check the coolant level.

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Let me know what you find or if you have other questions.

Take care,
Joe

Welcome back:

Those look normal. Have you ever checked compression? Does the engine have 200+K miles on it?

https://www.2carpros.com/articles/how-to-test-engine-compression

As far as the IAT, it looks right also. Were the temps cold approximately what the outside ambient temperature was?

Let me know.
Joe

Welcome back:

It may not be the problem. However, when the engine is cold, compression will be lower. Once it heats up and the metal expands, compression will increase. It's a thought at this point.

Let me know.

Joe

Welcome back:

Since you have a live data scanner, do me a favor. Have it plugged in before you try to start the engine. Have it so you can see the RPM signal. When you crank the engine, see if at first there is no signal and then it shows up and starts. This will be easier than the compression test. Let's eliminate an issue with the crankshaft position sensor.

Take care,
Joe

Welcome back:

Okay, no need for a compression test. It sounds great. And yes, when cranking it will show the RPM signal (around 200 rpm). I want you to try one more thing.

When you suspect a delayed start, do this first.

1) Turn the key from the off position to the run position (engine off) and count to 5.

2) Turn the key off and repeat step 1.

Do that 3 times and on the 4th, see if it starts faster.

Let me know.

Joe

Welcome back:

That sounds the same. I have to be honest. Is that how it always starts? It doesn't sound out of the ordinary. Having that many miles on it, I feel confident it has lost some compression which could delay it slightly, but considering the mileage, it doesn't sound bad.

Let me know.
Joe

Based on your last description, usually that indicates fuel pressure drop off. Have you checked that?

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

Joe

I'm not sure I understand. You said you don;t have a fuel pressure regulator and then said it wasn't drawing fuel through the vacuum line. Did you mean you don't have a fuel pressure gauge? Fuel pressure drop off can be caused by a few different thing. One of which could be a leaking fuel injector or a bad check valve in the fuel pump.

Let me know. Sorry for all the questions.

Joe