diff --git a/AMSS_NCKU_source/Z4c_class.C b/AMSS_NCKU_source/Z4c_class.C
index 3a53dc0..6f4cd27 100644
--- a/AMSS_NCKU_source/Z4c_class.C
+++ b/AMSS_NCKU_source/Z4c_class.C
@@ -485,7 +485,25 @@ void Z4c_class::Step(int lev, int YN)
   }
 #endif
 
-  // CA-RK4: skip post-prediction sync (redundant; ghost cells computable locally)
+  Parallel::Sync(GH->PatL[lev], SynchList_pre, Symmetry);
+
+#ifdef WithShell
+  if (lev == 0)
+  {
+    clock_t prev_clock, curr_clock;
+    if (myrank == 0)
+      curr_clock = clock();
+    SH->Synch(SynchList_pre, Symmetry);
+    if (myrank == 0)
+    {
+      prev_clock = curr_clock;
+      curr_clock = clock();
+      cout << " Shell stuff synchronization used " 
+           << (double)(curr_clock - prev_clock) / ((double)CLOCKS_PER_SEC) 
+           << " seconds! " << endl;
+    }
+  }
+#endif
 
   // for black hole position
   if (BH_num > 0 && lev == GH->levels - 1)
@@ -850,28 +868,25 @@ void Z4c_class::Step(int lev, int YN)
     }
 #endif
 
-    // CA-RK4: only sync after last corrector (iter_count == 3); stages 1 & 2 are redundant
-    if (iter_count == 3) {
-      Parallel::Sync(GH->PatL[lev], SynchList_cor, Symmetry);
+    Parallel::Sync(GH->PatL[lev], SynchList_cor, Symmetry);
 
 #ifdef WithShell
-      if (lev == 0)
+    if (lev == 0)
+    {
+      clock_t prev_clock, curr_clock;
+      if (myrank == 0)
+        curr_clock = clock();
+      SH->Synch(SynchList_cor, Symmetry);
+      if (myrank == 0)
       {
-        clock_t prev_clock, curr_clock;
-        if (myrank == 0)
-          curr_clock = clock();
-        SH->Synch(SynchList_cor, Symmetry);
-        if (myrank == 0)
-        {
-          prev_clock = curr_clock;
-          curr_clock = clock();
-          cout << " Shell stuff synchronization used "
-               << (double)(curr_clock - prev_clock) / ((double)CLOCKS_PER_SEC)
-               << " seconds! " << endl;
-        }
+        prev_clock = curr_clock;
+        curr_clock = clock();
+        cout << " Shell stuff synchronization used " 
+             << (double)(curr_clock - prev_clock) / ((double)CLOCKS_PER_SEC) 
+             << " seconds! " << endl;
       }
+    }
 #endif
-    } // end CA-RK4 guard
     // for black hole position
     if (BH_num > 0 && lev == GH->levels - 1)
     {
@@ -1543,7 +1558,7 @@ void Z4c_class::Step(int lev, int YN)
     }
   }
 
-  // CA-RK4: skip post-prediction MPI ghost sync (redundant; ghost cells computable locally)
+  Parallel::Sync(GH->PatL[lev], SynchList_pre, Symmetry);
 
   if (lev == 0)
   {
@@ -2105,9 +2120,7 @@ void Z4c_class::Step(int lev, int YN)
       }
     }
 
-    // CA-RK4: only MPI sync after last corrector (iter_count == 3); stages 1 & 2 are redundant
-    if (iter_count == 3)
-      Parallel::Sync(GH->PatL[lev], SynchList_cor, Symmetry);
+    Parallel::Sync(GH->PatL[lev], SynchList_cor, Symmetry);
 
     if (lev == 0)
     {
diff --git a/AMSS_NCKU_source/bssnEM_class.C b/AMSS_NCKU_source/bssnEM_class.C
index 4867600..e06b701 100644
--- a/AMSS_NCKU_source/bssnEM_class.C
+++ b/AMSS_NCKU_source/bssnEM_class.C
@@ -1221,7 +1221,25 @@ void bssnEM_class::Step(int lev, int YN)
   }
 #endif
 
-  // CA-RK4: skip post-prediction sync (redundant; ghost cells computable locally)
+  Parallel::Sync(GH->PatL[lev], SynchList_pre, Symmetry);
+
+#ifdef WithShell
+  if (lev == 0)
+  {
+    clock_t prev_clock, curr_clock;
+    if (myrank == 0)
+      curr_clock = clock();
+    SH->Synch(SynchList_pre, Symmetry);
+    if (myrank == 0)
+    {
+      prev_clock = curr_clock;
+      curr_clock = clock();
+      cout << " Shell stuff synchronization used " 
+           << (double)(curr_clock - prev_clock) / ((double)CLOCKS_PER_SEC) 
+           << " seconds! " << endl;
+    }
+  }
+#endif
 
   // for black hole position
   if (BH_num > 0 && lev == GH->levels - 1)
@@ -1665,28 +1683,25 @@ void bssnEM_class::Step(int lev, int YN)
     }
 #endif
 
-    // CA-RK4: only sync after last corrector (iter_count == 3); stages 1 & 2 are redundant
-    if (iter_count == 3) {
-      Parallel::Sync(GH->PatL[lev], SynchList_cor, Symmetry);
+    Parallel::Sync(GH->PatL[lev], SynchList_cor, Symmetry);
 
 #ifdef WithShell
-      if (lev == 0)
+    if (lev == 0)
+    {
+      clock_t prev_clock, curr_clock;
+      if (myrank == 0)
+        curr_clock = clock();
+      SH->Synch(SynchList_cor, Symmetry);
+      if (myrank == 0)
       {
-        clock_t prev_clock, curr_clock;
-        if (myrank == 0)
-          curr_clock = clock();
-        SH->Synch(SynchList_cor, Symmetry);
-        if (myrank == 0)
-        {
-          prev_clock = curr_clock;
-          curr_clock = clock();
-          cout << " Shell stuff synchronization used "
-               << (double)(curr_clock - prev_clock) / ((double)CLOCKS_PER_SEC)
-               << " seconds! " << endl;
-        }
+        prev_clock = curr_clock;
+        curr_clock = clock();
+        cout << " Shell stuff synchronization used " 
+             << (double)(curr_clock - prev_clock) / ((double)CLOCKS_PER_SEC) 
+             << " seconds! " << endl;
       }
+    }
 #endif
-    } // end CA-RK4 guard
     // for black hole position
     if (BH_num > 0 && lev == GH->levels - 1)
     {
diff --git a/AMSS_NCKU_source/bssn_class.C b/AMSS_NCKU_source/bssn_class.C
index 09881c6..eb84f8e 100644
--- a/AMSS_NCKU_source/bssn_class.C
+++ b/AMSS_NCKU_source/bssn_class.C
@@ -3349,7 +3349,27 @@ void bssn_class::Step(int lev, int YN)
   }
 #endif
 
-  // CA-RK4: skip post-prediction sync (redundant; ghost cells computable locally)
+  Parallel::AsyncSyncState async_pre;
+  Parallel::Sync_start(GH->PatL[lev], SynchList_pre, Symmetry, sync_cache_pre[lev], async_pre);
+
+#ifdef WithShell
+  if (lev == 0)
+  {
+    clock_t prev_clock, curr_clock;
+    if (myrank == 0)
+      curr_clock = clock();
+    SH->Synch(SynchList_pre, Symmetry);
+    if (myrank == 0)
+    {
+      prev_clock = curr_clock;
+      curr_clock = clock();
+      cout << " Shell stuff synchronization used "
+           << (double)(curr_clock - prev_clock) / ((double)CLOCKS_PER_SEC)
+           << " seconds! " << endl;
+    }
+  }
+#endif
+  Parallel::Sync_finish(sync_cache_pre[lev], async_pre, SynchList_pre, Symmetry);
 
 #ifdef WithShell
   // Complete non-blocking error reduction and check
@@ -3689,30 +3709,27 @@ void bssn_class::Step(int lev, int YN)
     }
 #endif
 
-    // CA-RK4: only sync after last corrector (iter_count == 3); stages 1 & 2 are redundant
-    if (iter_count == 3) {
-      Parallel::AsyncSyncState async_cor;
-      Parallel::Sync_start(GH->PatL[lev], SynchList_cor, Symmetry, sync_cache_cor[lev], async_cor);
+    Parallel::AsyncSyncState async_cor;
+    Parallel::Sync_start(GH->PatL[lev], SynchList_cor, Symmetry, sync_cache_cor[lev], async_cor);
 
 #ifdef WithShell
-      if (lev == 0)
+    if (lev == 0)
+    {
+      clock_t prev_clock, curr_clock;
+      if (myrank == 0)
+        curr_clock = clock();
+      SH->Synch(SynchList_cor, Symmetry);
+      if (myrank == 0)
       {
-        clock_t prev_clock, curr_clock;
-        if (myrank == 0)
-          curr_clock = clock();
-        SH->Synch(SynchList_cor, Symmetry);
-        if (myrank == 0)
-        {
-          prev_clock = curr_clock;
-          curr_clock = clock();
-          cout << " Shell stuff synchronization used "
-               << (double)(curr_clock - prev_clock) / ((double)CLOCKS_PER_SEC)
-               << " seconds! " << endl;
-        }
+        prev_clock = curr_clock;
+        curr_clock = clock();
+        cout << " Shell stuff synchronization used "
+             << (double)(curr_clock - prev_clock) / ((double)CLOCKS_PER_SEC)
+             << " seconds! " << endl;
       }
+    }
 #endif
-      Parallel::Sync_finish(sync_cache_cor[lev], async_cor, SynchList_cor, Symmetry);
-    } // end CA-RK4 guard
+    Parallel::Sync_finish(sync_cache_cor[lev], async_cor, SynchList_cor, Symmetry);
 
 #ifdef WithShell
     // Complete non-blocking error reduction and check