McLaren have suffered a dire start to pre-season testing, with a second consecutive day hit by major problems with Honda's new engine.
Belgian Stoffel Vandoorne completed only 40 laps - just 11 more than team-mate Fernando Alonso on Monday.
With a quarter of pre-season testing gone, McLaren have completed 69 slow laps. Mercedes have done more than 300.
Kimi Raikkonen's Ferrari was fastest on Tuesday, from Lewis Hamilton's Mercedes and Max Verstappen's Red Bull.
Vandoorne finished the day 10th fastest of 11 drivers and 4.6 seconds off the pace.
What's going wrong for Honda?
Honda has introduced a new engine layout for this season, following the design philosophy used by Mercedes since the start of the turbo hybrid formula in 2014.
Honda F1 engine boss Yusuke Hasegawa said at the launch of the McLaren car last Friday that he believed the Japanese company could match by the start of the season the power levels achieved by Mercedes at the end of 2016. Mercedes are understood to have made another step since then.
But the technology involved is complicated and Honda has so far not managed to make the engine work in the car.
On Monday, Alonso's problem was caused by a new oil-tank design that was not scavenging the oil effectively.
Vandoorne completed 29 laps on Tuesday morning before another engine problem kept him in the pits for several hours.
He returned to the track for the final hour but did just 11 laps. One was enough to move him off the bottom of the time sheets.
Honda has not yet said what the problem was with the engine Vandoorne used on Tuesday.
"We would have liked to put in more laps," Vandoorne said. "Hopefully overnight we can analyse what went wrong and come back with a reliable car tomorrow.
"This was my first day of testing, Fernando didn't get many laps in yesterday, so tomorrow and after tomorrow are going to be important days for us."
Mercedes and Ferrari on top
While McLaren toiled, Mercedes and Ferrari continued their impressive starts to their 2017 campaigns at Spain's Circuit de Barcelona-Catalunya.
Hamilton was fastest in the morning, when he completed 66 laps - the length of the Spanish Grand Prix.
Team-mate Valtteri Bottas took over the car in the afternoon and completed the first full race-simulation run of the winter.
But it was Raikkonen who set the pace, with a lap in one minute 20.960 seconds - 0.023secs quicker than Hamilton.
Raikkonen was using the 'soft' tyre when he set his lap and Hamilton the faster super-soft. But Hamilton lost 0.3secs in the last sector of the lap compared to his best time on the soft tyre, which suggests he could have gone faster.
It is in any case unwise to use headline lap times in testing as a guide to form as it is impossible to know the fuel loads of the cars, how hard the engines are being pushed or the specification they are running in.
Red Bull's Max Verstappen was third fastest, ahead of the Haas of Kevin Magnussen.
Bad start for Stroll
Williams rookie Lance Stroll had a difficult start to his 2017 campaign, spinning at Turn Nine after just 12 laps.
The 18-year-old Canadian damaged the front wing and that ended his running for the day as Williams needed to send back to their factory in Oxfordshire for replacements, which will not arrive in Spain until Wednesday morning.
"It is unfortunate," he said. "One front wing, a spin, a little winglet [damaged], but that is Formula 1. The car is very complex. There is not a lot of room for error.
"I'm just getting to grips with the car. A little spin. I drove back to the paddock. Sometimes these things happen, but no, not a dent in the confidence."
Day two times:
1 Kimi Raikkonen (Fin) Ferrari 1:20.960 *
2 Lewis Hamilton (GB) Mercedes 1:20.983 **
3 Max Verstappen (Ned) Red Bull 1:22.200 *
4 Kevin Magnussen (Den) Haas 1:22.204 **
5 Esteban Ocon (Fra) Force India 1:22.509 **
6 Daniil Kvyat (Rus) Toro Rosso 1:22.956 *
7 Valtteri Bottas (Fin) Mercedes 1:22.986 *
8 Jolyon Palmer (GB) Renault 1:24.139 *
9 Antonio Giovinazzi (Ita) Sauber 1:24.671 *
10 Stoffel Vandoorne (Bel) McLaren 1:25.600 *
11 Lance Stroll (Can) Williams 1:26.040 ***
*time set on soft tyres
**time set on supersoft tyres
***time set on medium tyres