Unexpected vibrations from the Honda engine are causing McLaren's power unit to effectively shake itself into breaking down, Sky Sports understands.

The McLaren-Honda MCL32 car crawled to a halt on four different occasions over the final two days of pre-season testing at Barcelona with Honda seemingly no closer to fixing an engine which Fernando Alonso described as offering "no power and no reliability" in a withering rebuke of McLaren's power suppliers.

Brown: McLaren not in crisis

The team, who had already endured an abject fortnight at Barcelona, completing the fewest number of laps and recording a fastest time three seconds adrift of the quickest lap, attributed Alonso's two on-track breakdowns on Friday to a 'a series of intermittent electrical issues'.

But it is understood that vibrations from the Honda engine are suspected to be the root cause of the outages.

"What's the issue with the engine? As far as I can glean, the issue is vibrations and so many vibrations that it is affecting the electrics and things are popping out left, right and centre," explained Sky F1's David Croft.

SKy F1's David Croft is joined by journalists Jon Noble and Chris Medland for this F1 Report - Testing Special in Barcelona. SKy F1's David Croft is joined by journalists Jon Noble and Chris Medland for this F1 Report - Testing Special in Barcelona.

The MCL32 also broke down twice on Thursday with the stoppages also attributed to electrical glitches. But in the wake of two more on-track failures on Friday, Honda acknowledged they were struggling to identify the cause of the breakdowns.

"It was unfortunate that we encountered the electrical issue again despite having replaced the parts under investigation overnight," said Honda F1 chief Yusuke Hasegawa. "This meant a significant amount of today's test was spent trying to identify what was causing the car to lose power."

McLaren themselves stated: "Overnight, the team changed a number of electrical components on both the PU and chassis, but the problem persisted. With every run in the morning session, the team changed further parts in an effort to eliminate as many variables as possible and identify the source."

"Although we've suffered a number of issues over the course of two weeks of testing, we've certainly learned a lot about the car, and we know the problems that need to be addressed," said McLaren chief Eric Boullier.

"Plainly speaking, they aren't overnight fixes, but we're hopeful both McLaren and Honda will be able to make progress on them ahead of Australia."

Speaking on the F1 Report - Testing Special, our guests think McLaren are a team in crisis following a disappointing display at testing in Barcelona Speaking on the F1 Report - Testing Special, our guests think McLaren are a team in crisis following a disappointing display at testing in Barcelona

Over the course of the two weeks of testing, McLaren are believed to have made more engine changes than will be permitted over the duration of an entire season without penalty and the need to run the Honda unit on reduced power has further restricted the team's analysis of their chassis.

"We have only one problem: that is the power unit," said Alonso during his solitary press briefing of the week.

Their fastest lap time of 1:21.348, set by Stoffel Vandoorne on the penultimate day, compared to the test-best of 1:18.634 by Ferrari.

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