Initially he was very quick in his EJ11, his fastest time of 1.20.089 was the quickest of the Honda powered cars and fourth overall. After setting his best lap he was stuck in the garage for a long time and the car seems to be suffering from over heating problems.
Just this week Trevor Foster admitted that the car was suffering from overheating problems, but suggested their problem had been identified and solved. It now appears there might be some work still to do.
As the engine is the same one that powers the BAR, and the BAR is not having heating problems, it would appear to be a car problem rather than an engine problem.

Overall though, Heinz seems happy. He doesn't appear to be concerned about the apparent speed of the BAR, Ferrari or Prost vars, it's the Williams that has caught his eye.
“The only thing I'm a bit worried about is how well Williams is doing,” he explained. “Ralf Schumacher was doing a long run in the past few days, so he had a sufficient fuel load onboard and his times were really impressive. Whatever has been said about the car, I feel that the Williams seems to be a pretty quick car.”