Chevrolet sorry for “freak” issue that cost O’Ward win at St. Petersburg

O’Ward qualified third for IndyCar’s season-opener and held station there for most of the race, behind Andretti Autosport’s Romain Grosjean and Colton Herta in the first stint, then behind Team Penske’s Scott McLaughlin and again Grosjean in the middle stint. The Mexican was therefore in prime position to inherit the lead when McLaughlin and Grosjean tangled on lap 72.

Despite O’Ward sprinting away from Ericsson’s Honda-powered Chip Ganassi Racing entry following the final restart, getting his lead up to 2.7s in two laps, this was mainly due to the Swede making a mistake at the restart and thereafter the gap began to close.

At the end of lap 96 of the 100-lap event, as he came off the final hairpin onto the pitstraight, O’Ward’s car lost power for one second, enough for Ericsson to surge past and into the lead that he retained to the finish.

O’Ward was furious that what was described as a “plenum event” in his Chevrolet engine had robbed him of a fifth IndyCar win.

Rob Buckner, Chevrolet’s IndyCar programme manager, was deeply apologetic for the loss and explained the issue on O’Ward’s 2.2-litre V6 twin-turbo engine.

“Architecturally our engines have two injectors per cylinder – a port fuel injector and direct injection right in the combustion chamber. During very heavy transient events, like Pato coming off the hairpin when we’re working the injectors pretty hard, it means at the top of the plenum on the engine there’s a lot of fuel and air mixture,” Buckner said.

“Essentially if you tickle the hard limiter or have heavy wheel-slip or then shift – or some quick combination of events – you get a once-in-a-million engine revolution-type combination of settings.

“If that lights off, then the fuel/air mixture in the plenum is fully consumed and the torque output of the engine plummets for a moment. For the driver, it feels like the engine has gone dead for a moment and typically he does what Pato did – lift off the pedal and essentially choke the oxygen going to the plenum, and extinguish that fire.

“Once you go back to power, the engine resumes and everything’s fine. Usually it doesn’t damage engines, doesn’t hurt the fuel components or anything in the combustion chamber.

Pato O'Ward, Arrow McLaren Chevrolet

Photo by: Gavin Baker / Motorsport Images

“Unfortunately, in the entire lifetime of this programme, that was the most consequential one we’ve had. Terrible timing. And it was absolutely on us. I hate it for the #5 car and hate it for Pato, because I’m very confident they had the race won without that. But we win together, lose together and we’ll move on. Personally, I wish we were going to Texas [scene of the second IndyCar round on 2 April] this Friday, because it stinks we have to wait a month to try and redeem ourselves.

“Everyone on the engine side puts in a ton of effort to make sure our calibrations are robust to try and ensure these types of things don’t happen. Unfortunately we haven’t been able to entirely eliminate these events.”

Asked why such an event might happen at that particular moment, Buckner said: “It has to be that perfect scenario for it to light off. In this case it was heavy wheel-slip, hitting the push-to-pass button, a little bit of hard limiter and then the shift. You could run that exact same sequence of events 50 more times and it probably wouldn’t happen. It’s that much of a freak occurrence. We had one or two over the entire weekend.

“I understand Pato’s feelings. From the driver’s seat, that had to be very, very frustrating. Typically when it happens it’s not while the leader is under pressure from behind with four laps to go. That’s about as bad as it can be and we have to own that.

“It’s just the limitations of the control strategy and the ECU. When you think of how quickly things are happening when you come off the hairpin, accelerating in a lower gear, hot day and the engines have been running hard for two hours so everything’s thoroughly heat-soaked.

“We’ve done everything we can to mitigate them, but we can’t eliminate the possibility entirely.”

Pato O'Ward, Arrow McLaren-Chevrolet

Photo by: IndyCar Series

Despite the inability to come up with a 100% guaranteed solution for the problem, Buckner vowed that Chevrolet and Ilmor staff would conduct a thorough investigation to see if they might further reduce the chances of a repeat.

“We’re going to look at every millisecond of what happened there – all the settings, all the inputs – and try to make our package even more robust,” he said. “Our goal is to make sure the engine can do what the driver’s right foot is telling it to do, and on this occasion, Pato had the throttle wide open and he lost power for around one second.

“Anything we can learn from that, we will. There was another [plenum event] one in the race for another of our cars, but that wasn’t consequential. There are a lot of differences between our fuel system and that of our competition [Honda] which maybe makes us more prone to a plenum event, but we’ll try and learn from it and have our system more robust for Long Beach [the next street race on the schedule].”