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2005 Xterra Off-Road 6MT. Built on 33" BFGs, Bilstein, Shrockworkx, Smittybilt, Total Chaos, & ARB
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Discussion Starter · #1 · (Edited)
Need some help on this one...

Cylinder 1 ignition coil-on-plug consistently overheats and ruptures causing misfire. Even with new spark plug. New coil lasted approximately 40 miles before rupture.

Only OBDII code is for cylinder 1 misfire.

Power distribution is in series to all coils from battery

Common engine ground to all coils intact

Main battery to engine ground strap intact

Trigger wire goes direct to PCM which decides timing telling coil to accept voltage in pulses for spark.
  • Possibly a short in PCM leaving trigger open, causing constant voltage at coil?
  • Trigger wire back to PCM shows continuity and low resistance
  • PCM was replaced and reprogrammed approximately 180k miles. Truck currently has 200k miles
Did continuity/ohm checks on entire wiring harness. 3 pins. Positive, ground, control. All pins show low resistance. Ground has continuity and same resistance as another functional plug

Voltage to cylinder 1 coil is 14.32v with engine running at idle. Consistent with other functional coils.

Using coil test light at idle seemed to show voltage pulsing pattern at cylinder 1 consistent with other functional coil, but the light seemed brighter? May have just been the position it was in?

Added two additional ground straps from engine block to frame and body. I doubt this will help anything.

Everything seems to be pointing to the PCM....

Anyone have any ideas??
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Need some help on this one...

Cylinder 1 ignition coil-on-plug consistently overheats and ruptures causing misfire. Even with new spark plug. New coil lasted approximately 40 miles before rupture.

Only OBDII code is for cylinder 1 misfire.

Power distribution is in series to all coils from battery

Common engine ground to all coils intact

Main battery to engine ground strap intact

Trigger wire goes direct to PCM which decides timing telling coil to accept voltage in pulses for spark.
  • Possibly a short in PCM leaving trigger open, causing constant voltage at coil?
  • Trigger wire back to PCM shows continuity and low resistance
  • PCM was replaced and reprogrammed approximately 180k miles. Truck currently has 200k miles
Did continuity/ohm checks on entire wiring harness. 3 pins. Positive, ground, control. All pins show low resistance. Ground has continuity and same resistance as another functional plug

Voltage to cylinder 1 coil is 14.32v with engine running at idle. Consistent with other functional coils.

Using coil test light at idle seemed to show voltage pulsing pattern at cylinder 1 consistent with other functional coil, but the light seemed brighter? May have just been the position it was in?

Added two additional ground straps from engine block to frame and body. I doubt this will help anything.

Everything seems to be pointing to the PCM....

Anyone have any ideas??
View attachment 127386
What brand of ignition coils are you using? How many have been damaged? When you pull the coil off the spark plug, is there engine oil in the "socket" that plugs onto the spark plug? Does the "on time" of the test light look the same when connected to Cylinder 1 as for the other cylinders? It the test light connected in place of the spark plug? Are you able to repeat the tests with the test light in a garage or some other place without direct sunlight affecting how the test light looks?

With the engine off (preferably with the battery disconnected), check the trigger signal for Cylinder 1 and several other cylinders as follows:
  1. Set your DVM/multimeter to the "diode" function.
  2. Unplug the harness to a coil.
  3. Connect the red DVM lead to the trigger signal pin at the connector to the coil.
  4. Connect the black DVM lead to the 12V pin at the connector to the coil.
  5. You should get a stable reading of something between 0.3V and 1.5V
  6. Connect the black DVM lead to the trigger signal pin at the connector to the coil.
  7. Connect the red DVM lead to the Ground/0V pin at the connector to the coil.
  8. You should get a stable reading of something between 0.3V and 1.5V
The readings for all cylinders should look about the same. If one of the cylinders gives a reading like "overload", it is possible that the output section of the ECU for that trigger signal has been damaged.

Do you have access to an oscilloscope and would you know how to use it? The trigger signal from the ECU to each of the ignition coils should be a 0V to 12V signal at low current. If I recall correctly, each ignition coil has a transistor in it that is controlled by the trigger signal. When the transistor turns on, it allows current to flow from the 12V supply line through the primary of the coil. If the signal from the ECU is shorted (stuck at 12V or 0V), you would not get any pulses on your test light. If the duration of the trigger signal for Cylinder 1 is significantly longer than the duration of the signals to the other cylinders, it could cause the coil on Cylinder 1 to overheat. If the shape of the trigger signal for Cylinder 1 is not "clean" and "square", it may cause a problem also.
 

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2007 OffRoad 6MT
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I don't know if you've figured out what was wrong yet, but when I was working at Infiniti we had an issue every once and a while on 1st gen FX35's where excessive resistance in the engine to body Gnds caused this issue.


EDIT: Just saw how old this is..... lol :rolleyes:
 
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