How much trouble is McLaren-Honda in?

This is a big season for McLaren-Honda. Two years into the troubled return of this famous Formula 1 alliance, it is high time it started consistently delivering the performance and results to suggest it can carry the fight to the championship's established big guns.

Honda has now spent two full seasons learning the intricacies of F1's mightily complex V6 hybrid turbo engine formula on track. It has not been an easy education. Its engines have lacked power, efficiency, reliability. But, they have been gradually improving.

As has McLaren. This proud winning team lost its way badly in 2013, and has been struggling to recover since. But again, there have been signs of improvement - infrastructural change, different working methods for conceiving and developing its cars, a feeling things are generally moving in a positive direction.

And yet the more things change the more they seem to stay the same.

On McLaren-Honda Mk2's very first track outing, at the post-season test in Abu Dhabi in 2014, electrical problems meant the mule car failed to complete a single flying lap.

A few months later, at the first pre-season test of 2015 at Jerez, McLaren-Honda completed just 79 laps across four days thanks to a glut of further engine problems - with sensors, electrical systems, the cooling systems, the oil systems. It was pretty much an unmitigated disaster.

Reliability was much improved in time for the first test of 2016 at Barcelona's Catalunya circuit. Honda produced a much more efficient and effective ERS system based on the lessons of 2015, but the overall performance of the engine was still disappointing, and that continued through the season.

One year further down the line, McLaren-Honda arrived at Barcelona with expectations of having a chassis that can rival the best teams on the grid - Mercedes, Red Bull and Ferrari - mated to a redesigned engine that is supposed to be able to at least match the level Mercedes' reached by the end of 2016, which is reckoned to be about 80bhp up on where Honda got to last year with its power unit.

The talk has been of renewal - new regulations, new car, new name for the car, new livery, new engine, new management. A clean break with the past. Time to get serious.

But three days into pre-season testing, it already looks as though McLaren-Honda is struggling.

The first two days were pretty much written off by engine problems. A fault with Honda's oil tank design lost Fernando Alonso his first morning in the car, requiring an engine change and the shipping of the faulty unit back to Japan for analysis, before Stoffel Vandoorne suffered a significant combustion engine failure on Tuesday.

Two days down, two engines down, only 69 laps on the board. And not even a proper run among them, according to Vandoorne.

Honda's ongoing investigations will reveal whether these problems are mere niggling glitches, such as those that befell Red Bull-Renault early on day one in Spain, or something more serious.

Like all manufacturers at the first pre-season test, Honda has been running its new power unit in a detuned state. But if Honda has to rethink its oil tank design, or discovers serious flaws in the new pre-chamber ignition technology it knows it needs to perfect in order to challenge the top manufacturers, that could have serious knock-on consequences when it comes to extracting further performance, with an updated Melbourne-specification of the engine due to arrive for next week's second test.

Mercedes, Ferrari and Renault are likely to stretch further away when they start turning up their new engines, especially if Honda is unable to do the same for fear of further failures.

This is probably why Honda's F1 engine chief Yusuke Hasegawa reckons it is "especially" important to find the root cause of Tuesday's combustion engine failure in particular, even though the team played down the likely impact of this week's problems on McLaren-Honda's ultimate development plan.

"We have many issues," admits McLaren-Honda racing director Eric Boullier. "None of them are fundamental. [On Wednesday] finally we can run, so we have some usual glitches - the ones you get on day one [normally] - but obviously we have them on day three.

"It is a new layout of the engine from Honda and obviously some unexpected glitches, but nothing is fundamental."

Day three was certainly better, with Alonso completing three more laps of Barcelona than McLaren-Honda managed across the previous two days combined. But as Mercedes, Ferrari and Red Bull filled the top three places on the timesheets, Alonso languished in 10th, almost three seconds off the pace.

What's more, the car did not look particularly impressive when it was circulating.

"I was concentrating on Turns 1, 2 and 3," says Autosport's technical consultant Gary Anderson. "It's a complex, so if you get Turn 1 right then Turn 2 becomes easier, which in turn makes Turn 3 easier.

"The Ferrari, for me, is without doubt the most stable car - millimetre precise and never really seeming to change line. You wouldn't know if it had five-lap old tyres or 25-lap old tyres on it, and it's good on both the soft and the medium compound.

"The Mercedes looks pretty reasonable on the soft tyres - still moving and with more understeer than the Ferrari - but not so good on the medium tyre, just no grip.

"Through that complex, the McLaren never looked good. Alonso couldn't get hard on the throttle out of Turn 2 - the car just starts moving - and I never saw him go into Turn 3 flat on the throttle.

"He's either having to lift big time beforehand, or just as he's coming into the corner. It's not understeer, just a lack of grip.

"McLaren can't really complain about Honda's engine, because there are still horses left in there that they're not using at the minute. It looks OK on the very softest tyres, but on softs and mediums - the most relevant tyres for this track - it's just not there."

McLaren's issues are not confined to the first complex, either.

"Up at Turn 9, the same thing," Anderson adds. "The Ferrari can commit properly on the way in, with barely a lift off the throttle. The McLaren can't do that. Obviously I don't know what the fuel loads are, but if Alonso doesn't lift and slow the car down on the way into the corner significantly, it won't go round properly. It doesn't look like it's got a horrendous balance problem, but it does look like it's got a grip problem.

"The Sauber is not a good chassis - that's one end of the scale. The Ferrari is at the other end of the scale. At the very best the McLaren is in the middle - and that would be giving it a pat on the back.

"I don't know how many McLaren people have been around the track, but I've been around it a few times, and I've never seen a McLaren driver able to commit. It's visible in both sound and vision."

McLaren is effectively two days behind its major rivals in terms of understanding its new package, thanks to those earlier engine problems. Disregarding Alonso's 'headline' time on ultra-softs on Wednesday, the McLaren lapped in 1m23.8s on the soft compound, which is around two seconds slower than Mercedes and Ferrari managed on day one, and just under a second shy of where Red Bull got to after its disrupted first morning.

Anyway you slice it, there is still some serious work to do - with both the chassis and the engine.

"Even the perfect car, when you push to the limit you will always have understeer, oversteer, or something like this," argues Boullier. "But both drivers don't complain, and feel that the base of the chassis is good, so we can develop around this.

"There will be a high development rate, especially for the beginning of the season. I expect most of the teams to bring nearly a new car in Australia."

But can we realistically expect a big shift in the right direction for McLaren-Honda's fortunes? A slow start seems more likely.

Honda still seems to be struggling to get properly on top of this engine formula, which must be putting a strain on intra-team relations, even though they have yet to descend to the level of public recrimination we witnessed between Red Bull and Renault in 2015.

Alonso has put a brave face on things in public too, but quietly he must be seething at the thought of potentially seeing his three-year stint with McLaren-Honda go to waste in uncompetitive machinery.

The more time passes, the more McLaren's decision to give up Mercedes customer power for this works partnership with Honda looks like a big mistake. At least with a Mercedes engine in the back, we would know for sure how capable the McLaren chassis really is.

Now a McLaren-Honda reserve and ambassador, Jenson Button knows what it's like to jump into a brand new car, developed for a major rules overhaul, and feel from the earliest laps of pre-season testing that he's onto a winner. It's highly doubtful Alonso and Vandoorne have felt anything close to that sensation in Barcelona this week.

The McLaren-Honda project feels like Groundhog Day - valiant attempts at doing things differently that ultimately seem to lead back to the same starting point.

At some point, serious questions will have to be asked internally about whether this troubled partnership is truly a sustainable proposition. Honda has been successful in F1 before, but during an era when it lacked credible opposition. That is certainly not the case today.

Honda hasn't been truly competitive in Formula 1 since the early '90s; McLaren hasn't been truly competitive in Formula 1 since 2012. The longer this elongated mutual drought of success continues, the more danger there is of both organisations suffering irrevocable damage.

Perhaps all will be well in the end. Perhaps more track time and development and set-up work will bring the MCL32 to life. Perhaps Honda will fix its early problems, turn up its new engine, and finally prove itself to be a serious player in Formula 1's V6 era.

Or perhaps not. In which case the writing could be well and truly on the wall for the McLaren-Honda dream.