Why cant I tune my replacement vehicles?

[fpspiers]

Hi,
Im relatively new to modding but am familiar with openiv. Ive installed numerous replacement and add on vehicles recently without issue. The tuning worked correctly on the replacement vehicles until now, when I attempt to tune one of them it installs the parts of the vanilla vehicle that was replaced instead of the modded vehicles parts.

What causes this and how can I fix it?

Thanks

[baneofpoo2]

not all replace vehicles have tuning parts or they're just installed incorrectly or not installed at all

[fpspiers]

The ones in question do have parts because they were working fine for me. They just randomly stopped working, for all my replacement vehicles