Pre-glow & start problems (2.5 D, year 1999, 2499 cm3, 80 hp, 59 kW, HSN/TSN 3004 540)

Hello first to everyone, I have a question for you again. I have been having problems starting for a few days. The lamp goes out after about 10 – 15 seconds but don’t start, I have to do it about 5-10 minutes and because he jumps on, rust short but runs quite normal. Can you give me a pair of tips as I can check where and what I should do about it? Would you be very grateful for any information. Thank you in advance.