Do they mean the same?

[dilodi83]

Do they mean the same? Are they all grammatically correct?

1) By the time we have arrived, he will have left.
2) By the time we arrive, he will have left.

1) Since they started producing the more modern 306, they have sold this type of car less well.
2) Since they started producing the more modern 306, they have been selling this type of car less well.
3) Since they started producing the more modern 306, this type of car has been selling less well.

[bhaisahab]

Do they mean the same? Are they all grammatically correct?

1) By the time we have arrived, he will have left.
2) By the time we arrive, he will have left.
#2 is correct, #1 is not ungrammatical but it's not natural English.
1) Since they started producing the more modern 306, they have sold this type of car less well.
2) Since they started producing the more modern 306, they have been selling this type of car less well.
3) Since they started producing the more modern 306, this type of car has been selling less well. These three mean the same and are correct, #3 is the most natural.

Bhai.

[RonBee]

Re:
.

By the time we have arrived, he will have left.

.
While that might be grammatical, I think you would be hard pressed to find anybody who actually talks that way. (B touched on that already with his comment about it not being natural English.) More likely:
.

By the time we get there, he will have left.

~R