caterpillar 518 skidder

Sounds likely to me! I know it doesn't happen every time, but it sure fits in this case.

Have you loosened each injector line in turn to see if you can eliminate the knock and smoke by cutting out one cylinder/injector? Maybe the knock and smoke are from different ones😮

At the very least you will have it bled out good.

Thanks for the reply. The day after I posted this we got about three feet of snow. Had a few warm days this week that took the snow down some so I messed with the skidder today. When you crack the second injector back from the front of the engine the smoke and knock goes away. So I guess I found my problem. Now for the next question. Do you need any special tools to get the injectors out? Also do I have to replace the whole injector or is just the tip replaceable? The engine is a 3304. Thanks