NodeMCU programming without USB port

Development Tools IDE 1.x
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Recently, I've been attempting to build an anti-collision detection system for uses in a car. I bought Several nodeMCU units and will use one as WiFi Hub.

In the course of experimenting, I broke off the micro-USB connectors of two of the units. I have since purchased a hot glue gun and glued the other two down.

The problem is programming without a USB connector. I've read elsewhere, a USB-to-serial adapter/converter can be used. The units are common and feature the FTD232RL chip with the power jumper set to 3.3V. I have several. What I've read states that the FLASH button is held down while the RESET button is "tapped." This establishes bootloader mode.

I'm not sure what I'm doing wrong, but this doesn't work for me. One of the two USB-less units contains a program that runs whenever I plug it in. That unit has a 5v power supply soldered to the Vin/GND pins. After trying to follow the steps, the original programs still runs when the unit is plugged in.

The Arduino IDE compiler attempts to connect to the unit via a Windows COM port but times out. When I hold the FLASH button down and push the RESET button, I then release the FLASH button. There is a quick blip of the blue LED, then the LED comes on and stays on for about 10-15 seconds. Is this to be expected?

I also tried with the other USB-less unit which has a couple of wire leads soldered to the ESP chip to replace a broken FLASH button. The same thing happens.

Any ideas?

This is the wiring setup: ESP USB2Serial

Tx / Rx
Rx / Tx
Vin / 5V
GND / GND

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Basically the flash button is connected to GPIO 0 & GND, holding it down, while resetting the unit should put it into flash-mode, which means that you program shouldn't run, and you should be able to upload.
Now normally the GPIO pins on an ESP8266 are not 5v tolerant, but on most nodeMCU's GPIO3 (RX) is the exception.

every time you reset it, you will have to repeat Grounding GPIO 0, in fact easiest is probably to just connect a jumper wire between GPIO 0 & GND, until you have successfully uploaded a new sketch (there is no harm in that)

No, not really. On most nodeMCU's the blue LED is connected to GPIO 2 (active LOW) , a short 'blip' may indicate a reset of the board, GPIO pins have short pulses on them right after reset many times, there documentation about that, but let's not worry about it.

That looks fine, but just connect GPIO 0 ( D3) to GND as well while you are trying to upload.

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