fuel injector replacement
 

How may miles are the fuel injectors good for. My 300sel 3.0 has 160,000 and runs fine except it's hard to start when engine is cold or hot.

honestly, bosch tells you 100k is about it. by the time you pull 'em and clean 'em, that doesn't fix what's worn, only dirty. get injectors, holders and seals and you'd be suprised at the difference. good luck, chuck.

New injectors
 

When installing new injectors do they need any testing or cleaning? Do I just install and hope they work?

No cleaning / testing needed.
 

I replaced the injectors on my BMW 735i at about 165k miles, and the process was quite simple. No testing / cleaning was needed. The injectors that I pulled out looked dirty, and I did notice some very small performance improvement. Don't expect it to feel like a new engine, however.

troy
1995 E420 75k

the injectors in the 735 are opened electrically, not just mechanically. the kjet injectors have a spring that gets weak and a valve face and seat like an engine valve. you do a valve job you repair/replace those surfaces. with the injector, you replace because there is no disassembly. the electronic injectors CAN be disassembled and rebuilt, if neccessary.

the new injectors SHOULD be cleaned and tested for defects. it does happen. had a 560sl that i put injectors into and 1 of them created a miss. shoulda tested them first. good luck, chuck.