Grub - Install on flash drive

[casemod]

I run a portable installation of linux on a USB Hard drive. I have, however, recently acquired a laptop that refuses to boot from it.
I reformatted and updated grub, which made no difference. Installing grub on the internal HDD correctly shows the boot menu and allows it to boot from the USB HDD, but this seems to delete grub from the USB HDD.

I am wondering if there is a way to install grub into a USB Flash drive and direct it to the USB hard drive, but keeping the original boot grub (on the USB HDD) intact so that any other PC can boot from it?

Many Thanks

[p.H]

a laptop that refuses to boot from it.

Can you elaborate ? What do you do to boot from it, and what happens ?
Is it BIOS/legacy or native EFI boot ?
How is the USB drive partitioned ?

Installing grub on the internal HDD correctly shows the boot menu and allows it to boot from the USB HDD, but this seems to delete grub from the USB HDD.

"It seems" ? How do you know ? Please show evidence.

How do you install GRUB ? Which exact command, which parameters, which / and /boot ?

[casemod]

I press F9 and select the USB device to boot. The computer says boot from usb device failed. As noted it only happens with this particular laptop (an early i3 toshiba C660).
I have the drive partitioned as MBR with 3 partitions: Home (EXT4), System (EXT4) and swap. Drive is MBR and the system is set up for BIOS/Legacy boot.

I installed grub using a boot repair disk. Here's the link for the download page: https://sourceforge.net/projects/boot-repair-cd/.

I don't have any evidence other than after installing grub into the internal hard drive for said laptop the USB drive was no longer bootable on other computers. This is mostly an automated repair tool, hence I am looking at how to make it manually to set up my options.

Thanks!

[p.H]

The computer says boot from usb device failed

Is this the exact and complete error message ?

I have the drive partitioned as MBR with 3 partitions: Home (EXT4), System (EXT4) and swap. Drive is MBR and the system is set up for BIOS/Legacy boot.

Does one primary partition have the "boot" flag set ? Although it is useless when GRUB is installed in the MBR, some firmwares require it.

I installed grub using a boot repair disk.

This does not tell me much about how GRUB was actually installed. I do not trust these automated tools, as you never know what they actually do and may do more harm than good. Their only useful feature is the inclusion of boot-info-script which gathers a lot of information.

I don't have any evidence other than after installing grub into the internal hard drive for said laptop the USB drive was no longer bootable on other computers.

You could at least decribe what happens when you try to boot from the USB disk on another computer.
BIOS error ?
GRUB error ?
Other error ?

[casemod]

Does one primary partition have the "boot" flag set ? Although it is useless when GRUB is installed in the MBR, some firmwares require it.

Excellent! I set the partition with the boot flag and it went right through! Thank you.