diff --git a/Tools/autotest/arducopter.py b/Tools/autotest/arducopter.py
index 1de6f855c4..fe808916d4 100644
--- a/Tools/autotest/arducopter.py
+++ b/Tools/autotest/arducopter.py
@@ -1374,7 +1374,10 @@ class AutoTestCopter(vehicle_test_suite.TestSuite):
 
         # cut motor 1's to efficiency
         self.progress("Cutting motor 1 to 65% efficiency")
-        self.set_parameter("SIM_ENGINE_MUL", 0.65)
+        self.set_parameters({
+            "SIM_ENGINE_MUL": 0.65,
+            "SIM_ENGINE_FAIL": 1 << 0, # motor 1
+        })
 
         while self.get_sim_time_cached() < tstart + holdtime:
             m = self.mav.recv_match(type='VFR_HUD', blocking=True)
@@ -3285,8 +3288,8 @@ class AutoTestCopter(vehicle_test_suite.TestSuite):
                 self.progress("Killing motor %u (%u%%)" %
                               (fail_servo+1, fail_mul))
                 self.set_parameters({
-                    "SIM_ENGINE_FAIL": fail_servo,
                     "SIM_ENGINE_MUL": fail_mul,
+                    "SIM_ENGINE_FAIL": 1 << fail_servo,
                 })
                 failed = True
 
@@ -3345,10 +3348,7 @@ class AutoTestCopter(vehicle_test_suite.TestSuite):
                 raise NotAchievedException("Vehicle is descending")
 
         self.progress("Fixing motors")
-        self.set_parameters({
-            "SIM_ENGINE_FAIL": 0,
-            "SIM_ENGINE_MUL": 1.0,
-        })
+        self.set_parameter("SIM_ENGINE_FAIL", 0)
 
         self.do_RTL()
 
@@ -4170,8 +4170,7 @@ class AutoTestCopter(vehicle_test_suite.TestSuite):
         self.takeoff(40)
         self.set_rc(9, 1500)
         self.set_parameters({
-            "SIM_ENGINE_MUL": 0,
-            "SIM_ENGINE_FAIL": 1,
+            "SIM_ENGINE_FAIL": 1 << 1, # motor 2
         })
         self.wait_statustext('BANG! Parachute deployed', timeout=60)
         self.set_rc(9, 1000)
@@ -4184,8 +4183,7 @@ class AutoTestCopter(vehicle_test_suite.TestSuite):
         self.takeoff(loiter_alt, mode='LOITER')
         self.set_rc(9, 1100)
         self.set_parameters({
-            "SIM_ENGINE_MUL": 0,
-            "SIM_ENGINE_FAIL": 1,
+            "SIM_ENGINE_FAIL": 1 << 1, # motor 2
         })
         tstart = self.get_sim_time()
         while self.get_sim_time_cached() < tstart + 5:
@@ -12024,8 +12022,8 @@ class AutoTestCopter(vehicle_test_suite.TestSuite):
         self.context_push()
         self.context_collect('STATUSTEXT')
         self.set_parameters({
-            "SIM_ENGINE_FAIL": 1,
             "SIM_ENGINE_MUL": 0.5,
+            "SIM_ENGINE_FAIL": 1 << 1, # motor 2
             "FLIGHT_OPTIONS": 4,
         })
 
diff --git a/Tools/autotest/quadplane.py b/Tools/autotest/quadplane.py
index 721752a5c3..95e72e276f 100644
--- a/Tools/autotest/quadplane.py
+++ b/Tools/autotest/quadplane.py
@@ -767,8 +767,7 @@ class AutoTestQuadPlane(vehicle_test_suite.TestSuite):
                              "Q_WVANE_ENABLE": 1,
                              "Q_WVANE_GAIN": 1,
                              "STICK_MIXING": 0,
-                             "Q_FWD_THR_USE": 2,
-                             "SIM_ENGINE_FAIL": 2}) # we want to fail the forward thrust motor only
+                             "Q_FWD_THR_USE": 2})
 
         self.takeoff(10, mode="QLOITER")
         self.set_rc(2, 1000)
@@ -785,7 +784,7 @@ class AutoTestQuadPlane(vehicle_test_suite.TestSuite):
         self.set_rc(2, 1500)
         self.delay_sim_time(5)
         loc1 = self.mav.location()
-        self.set_parameter("SIM_ENGINE_MUL", 0) # simulate a complete loss of forward motor thrust
+        self.set_parameter("SIM_ENGINE_FAIL", 1 << 2) # simulate a complete loss of forward motor thrust
         self.delay_sim_time(20)
         self.change_mode('QLAND')
         self.wait_disarmed(timeout=60)
@@ -1475,7 +1474,10 @@ class AutoTestQuadPlane(vehicle_test_suite.TestSuite):
                     (p, new_values[p], threshold))
 
         self.progress("ensure we are not overtuned")
-        self.set_parameter('SIM_ENGINE_MUL', 0.9)
+        self.set_parameters({
+            'SIM_ENGINE_MUL': 0.9,
+            'SIM_ENGINE_FAIL': 1 << 0,
+        })
 
         self.delay_sim_time(5)