FTDI USB to rs232 problems

Hello Peter,

The USB disconnect could be caused by EMC possibly from the engine.

You could try increasing the reset pipe retry count described in section 5.1of our advanced drivers application note


5.1 Adjusting the Reset Pipe Retry Count

In some rare cases, it may be necessary to increase the number of times the driver tries to reset a USB pipe on which an error has occurred, for example in noisy environments where a lot of USB errors occur.

The default value for the reset pipe request retry count is 50. This default value may be changed in the FTDIBUS.INF file by editing or including the following fragment.


AddReg? = FtdiBus?.NT.AddService?.AddReg?



In this example fragment, the reset pipe request is set to 100.

This value is held in the registry key located at


Car 1

Made a rally BMW 325 install. When making the set up I had no problems but suddenly when driving Vt louse connection and says “unplug usb adapter”

Usb adapter is type

Driver is updated to the lasted one

Using Win Xp

Vt 2011-03-11

Firmware 1.1.81

Wiring harness typ vems 6 cyl.

The installation is made like this

Car 2

Consumer installation BMW 325 turbo.

They has the same problems and we tried to help but nothing will fix the serial problem.

Frimware 1.1.88

Vt 2011-04-26

Win xp

ftdi driver

Can I change settings in Vt or will it help (timeout, ignored error, write delay)

It will be helpful if someone could help out on this one

Thanks Peter

Regarding settings in vemstune, as long as write delay is >25 and timeout is 100 it is not related to that.

It is most likely related to ignition noise, broken spark plug, distributor or plug wires.


Also, PC (even a desktop) with real serial port often helps.

We have 2 wireless systems working (that can soon help installers with windows-usb-driver PITA), one with Wifi router (OverTCPWireless), the other (physically smaller) with bluetooth. We're also working on zigbee.