The most common and most likely answer to this crossword clue is the 5 plus 4 letter word SPARK PLUG
I've seen this crossword clue in The Guardian
S
P
A
R
K
P
L
U
G
More clues leading to the result SPARK PLUG
- Stimulate boxer to eat large starter
- Special old box and trailer is part of car
- Muriel, maybe, with advert for engine part
- Sit quietly feeding bullet, firing device
- Place power in bullet — that should get things motoring!
- Southern plonk promotion: ‘It ignites!‘
- Part of car where electrician briefly has trailer attached
- Supplier’s first to stop advert for engine component
- Inspiration to promote auto component
- It ignites quarrel and Grandad’s in bits
Buddy explains!

The straight part
We know that "Part of car" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case part of car = spark plug.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.