Hi Roland,
I suppose you are using fsl_lpuart component from SDK. There is known issue - the LPUART device clock source selection in SIM device is not done by the fsl_lpuart component (the default value is "clock source disabled"; see the after reset value of LPUART0SRC bits in SIM_SOPT2 register). This defect has been fixed in the upcoming SDK 1.1 release (it will be publushed soon).
You can use the following workaround:
Disable autoinitialization in the Component Inspector of the fsl_uart component in the project:

And use the following initialization code of the fsl_lpuart component in your application (it must be used after PE_low_level_init() call in the main() function). See example below:
int main(void)
/*lint -restore Enable MISRA rule (6.3) checking. */
{
/* Write your local variable definition here */
const uint8_t test_data[10] = "123456789";
uint32_t test_data_size = 9;
/* definition of LPUART state structure */
lpuart_state_t fsl_lpuartCom1_state;
/*** Processor Expert internal initialization. DON'T REMOVE THIS CODE!!! ***/
PE_low_level_init();
/*** End of Processor Expert internal initialization. ***/
/* Write your code here */
/* Selects the clock source for the LPUART0 transmit and receive clock.
*
* Values:
* - 00 - Clock disabled
* - 01 - IRC48M clock
* - 10 - OSCERCLK clock
* - 11 - MCGIRCLK clock
*/
CLOCK_SYS_SetSource(kClockLpuart0Src, 0x3 /* LPUART0SRC - MCGIRCLK = 0x3 */);
/* fsl_lpuart component initialization; lpuartCom1_InitConfig0 structure is generated by the fsl_lpuart component */
LPUART_DRV_Init(FSL_LPUARTCOM1,&fsl_lpuartCom1_state,&lpuartCom1_InitConfig0);
/* send test data in a loop */
for(;;) {
LPUART_DRV_SendData(FSL_LPUARTCOM1, test_data, test_data_size);
}
. . .
The clock source is selected in the SIM device (LPUART0SRC bits in the SIM_SOPT2 register) and the baudrate is correctly initialized by the LPUART_DRV_Init() method.
Best Regards,
Marek Neuzil