HPD race team leader Allen Miller admitted that there has been a common theme to most of the blow-ups, although Oriol Servia’s smoky retirement from yesterday’s practice session was caused by “something totally different.”

Miller told Motorsport.com: “The problems that [Sebastien] Bourdais and [Charlie] Kimball had at the Grand Prix were the same issue as Graham Rahal had in the first day of practice, then Bourdais again, and which had started happening to Alonso’s engine a couple hours before qualifying.

“We had less than two hours before the #29 car had to roll through tech so I said, ‘We can start inspecting before a decision. But if we start tech and I say ‘Change it,’ we’re not going to have time.’ So my decision was to just change it, and we’ll look at the one we took out afterward.

“It was the right call; it wasn’t dead but it had a concern. We could see from the data that Alonso would have had a problem.”

Although Miller couldn’t talk about the problems, he admitted that HPD is still struggling to identify their cause and therefore the possible solution.

“We had some issues earlier in the season [DNFs for Andretti Autosport’s Alexander Rossi and Takuma Sato at Long Beach] and we put out a different batch and updated engines, but it seems like we still have a problem and we still can’t lock it down to whether it’s a quality issue or a design flaw. The design says everything should be good.

“So anyway, we’ve been frantically working away to discover what’s causing our issue.”

Asked if it was something that could be cured by “turning down” the engine, Miller said not.

“We’re still investigating that but I don’t think it’s related,” he said. “I felt no more or less confident turning them up to 1.4-bar for qualifying. And anyway, turning down the engines isn’t something we want to do for the race.

“We’ve done quite a lot of testing over the past week, trying different operational changes and we’ve not come up with hard and fast solutions yet. We’ve got a few more days and we’re continuing to investigate. At this point there’s no option to change hardware; we have what we have. So we’re looking at how best to proceed and get the best results we can.”

Asked if it could be something as fundamental as a metallurgic problem, Miller replied: “Yeah, could be. That’s part of what we’re going through now. Is it a material problem, a manufacturing problem, or something related to assembly? We’re looking at everything. And given how hard we’re pushing the engines, it’s not surprising that new problems occur.

“Jack Harvey’s engine failure was something new compared to the others we mentioned, and then Servia’s was something completely unrelated to the others.”

Wary of Chevrolet challenge

Although Honda took pole position and six of the top nine grid slots, Miller said he was was not underestimating the potential opposition from the Ilmor-built Chevrolet units for race day.

“We’ve worked with Ilmor before and as we’ve continued to push, they’ve continued to push,” he remarked. “We don’t ever count those guys out. They’ve just replaced their engines with race engines and we don’t know if they have something that hasn’t been seen yet this year.

“Whatever you use as your Indy race engine is the spec it must remain for the rest of the year. It locks down any of the open items, any of the new annual homologated parts. So was everyone showing everything they had yesterday? I don’t know. It’s interesting, isn’t it?

Miller said that it’s at the engine manufacturers’ discretion regarding when raceday engines are installed, but that, like Chevrolet, Honda will fit its latest units in time to run them in the one-hour practice on Carb Day (Friday).

“We are fitting ours now, before Carb Day, so we have a chance to check there are no leaks and issues. You really don’t want to do it afterward because there is no more track running after that.

“Because of what happened in qualifying, Alonso is already using his race engine, and yeah, I’m confident in it to the extent that I can be. We’re researching everything within the engines and making sure who has what and whether there anything we need to do differently.

“We track serial numbers so we have a list of who’s got what, but as soon as you have one problem it makes you suspicious of every other engine.”