Lupo 3L doesn’t start anymore. Troubleshooting

Hello we have a problem with our Lupo 3L Bj.2002. He does not jump any more. We were shopping and when we wanted to go home he has to gelled but did not come to cover up after 10. After that he ran for a time again quite normal. Then when my mother drove, he just went out after 1km during the ride and did not jump any more. Have read out error memory but it was nothing in it. He also makes quite funny noises when letting loose the deed. Have once solved a screw on the tandem pump (was only minimal diesel in it), where you can measure it with a pressure tester or so and when igniting nothing came out, but what should happen in our opinion. It looks as if the tandem pump is over but how can you go quite safely there? Could it also lie to the relay or can someone help me find the error. Selection device is available. Must get the Lupo back to run. / / A month ago the fuel pump was changed, double temper/citation and a new one.