injine not sart after heating

[baksis]

i have savana 2002 and one day i have a water wit a sand get inside the engine
we changed the ring's set and we put a new over all set new oil and also i changed the pmd (the computer for the fuel bur after whene the ingin is cold it is starting in 1 second but whene it worm about 80-90 deg it's not starting and have a low starter it's look like hard start after cooling it start again so you have any cloo how to fix it and what do i need tu buy

thanks alot