Ground Problem?

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Lincoln Electric 175SP, 030 wire, 75/25 gas, 1/4" and 3/16" new mild steel, gas flow at 18 cfm (iirc).  Everything was fine until the last 20% of the welding.  Started with typical "frying" sounds, arc and puddle very visible and easy to manipulate and control.  As I got down to some finishing touches,  I started getting a "hissing" sound and not what I started with. The tip of the wire was bright, but could not easily see any puddle.  Definitely no splatter, just kind of balling up on the surface and I feel like no penetration.   Since it is is 4 am  and I started measuring and cutting out my pieces hours ago. I am going to bed and start tomorrow by grinding out the last few beads and re-do them.   I was wondering if I might not have attained a very good ground?  I try to keep my ground closer, rather than farther from the point where I am welding.  I am not sure what may have changed.  I wonder if the new steel might have had something to do with it?  I had wiped it down good, or I thought I had. Any comments, suggestions, griping, cussing, accusations, etc., are much appreciated! Thanks for the help
Reply:I've got two guesses.  Make that three.Exceeding duty cycle and the arc going wonky.Tip getting dirty/hot and restricting the wire.Bad connection in your ground wire. At the machine.  At the clamp. Or somewhere in between.  If a bad connection gets hot the resistance goes up.  Feel your ground for warm spots carefully after running a few heavy beads.My name's not Jim....
Reply:my guess is the duty cycle as well. it still gets me confused when I start to hit that - "why is this thing not working right?" - after a significant amount of frustration then I remember.Weldanpower 225 G7Ironworkers Local #24
Reply:Also check for a loose tip. Doesn't happen very often so it catches me off guard every time. Repeated heat/cooling cycles and they'll sometimes work theirself loose. Poor contact is poor contact. Doesn't matter which end it happens on."The things that will destroy America are prosperity at any price, peace at any price, safety first instead of duty first, the love of soft living and the get rich quick theory of life." -Theodore Roosevelt
Reply:Just had a similar problem earlier this week, ended up being a dirty liner. Loose/dirty tip is what I first thought of.  I use ideal arc 600's so I'm not sure what happens when your duty cycle catches up with you...Tandem Lincoln Power Wave AC/DC 1000's ~ Twin Power Feed 10A Controllers ~ 5/32" L-61 1000lb Speed Feed drums ~ 980 fluxDC1500 with NA3 ~ 3/16" L-50 60lb coil ~ 980 flux(2) Idealarc DC600's ~ .045" & 1/16" L-56 Barrels w/ C15 ~ Arc Gouging
Reply:Thanks for all of the helpful ideas to check.  The tip was loose, but I think the duty cycle may have been a partial factor, too. The next day, I  checked everything suggested and found the loose tip.  Just because my ground looked dark and corroded, I disassembled it and cleaned it up.  Everything was back to normal, then. Same tonight with some little projects to work on. Sorry for the slow reply, but I did take time to read all of the suggestions and make sure that each idea was followed through on. Thanks again!