Is it worth the gamble buying used injectors? Any way to tell they are high mileage by just looking? I have seen some high mileage injectors before the top of the solenoids looked pitted and the numbers were faded. He is asking 300 so I guess if nothing else that is fairly cheap core costs.

 

No way to tell without tearing them down...

AA's came in 95-96 trucks and most 97's, AB's came in cali 97's and E99 trucks and AD's came in the 99.5-2003 superdutys...

some 94.5's had AO injectors... same as a AA

 

OK so would a shade tree mechanic be able to tear them down and tell the condition?
One of the injectors is lightly carbon covered at the very bottom up to the first O-ring.
Is this caused from the O-ring leaking?
The solenoids appear to have not been exposed to excess heat.

 

The best you can do is take off the solenoid and use a feeler gauge to measure the armature clearance. If you can't get a .002" feeler gauge, they are shot. Other than that, you would need to take to a diesel shop to have torn apart and checked, then flow tested.

 

Could not have said it better myself...