The changeable weather in Melbourne and a lack of pace hampered the Prodrive Racing team at the Sandown 500 on Sunday.
Defending series champion Mark Winterbottom finished 24th to fall to fifth and behind Scott McLaughlin in the overall standings.
"It was a long day," Winterbottom said. "The car wasn't quite there. We need to get our speed back. Yesterday and the day before was pretty ugly.
"To actually get our car in the race then and see Dean [co-driver Dean Canto] doing good sectors was really promising. I was looking forward to getting in but in the Championship we're nowhere now.
"We'll try and win Bathurst, we'll try and win the next ones and push on but we need a quick car. The car's inconsistent. Today it was good and we wasted it but Dean did a really good job. I was really happy with how he went in the car."