ut,

You have a low pressure problem. Don't know if it's a cracked lateral pipe(look for wet spots) or the system was designed inadequately and/or heads added on later. How many heads are there on the zones that work well and what type and size of heads are they? Do some comparisons with the good zones. You might have a valve in the bad zone that only opens partially. Maybe your water source has had a pressure change over time. Old heads that leak by the stem leak pressure as well making the situation worse. Aloha

It has ten heads on it, as does the other line in that part of the yard -- kind of the far end of how many you want on one line, but I've put low flow heads on them to help. The other line with ten heads pops and this one doesn't. However, I may have just located the problem. I got to thinking that the one consistent issue has been the blow by on the last head on the line. I propped it in the up/open position and tried turning on the water & it popped multiple times with no problem. So, thinking the problem may be the blow by caused by the leak on that head, I replaced the head with a new body I had. After replacing it, the line pops and I was even able to open up the ones I had closed and it still pops. Time will tell . . .