2000 Other Jaguar Models Oil pressure low ?

My Jav 4.0V8 engine after a timeing tensioner replacement (at home), maybe too many dirt went into the engine ? The oil pressure lamp didn't switch off. I replaced oil (it was dirty) and filter, after replace, at the first some minutes the engine worked well, but after that the oil pressure lamp switched on again. My I replace filter and oil again or what can I do ?

Thank you for your help,
Istvan from Hungary