Blowing spark plugs
Fleet Owner
Joined: Mar 2003
Posts: 24,724
Likes: 74
From: Blue Hill Township
Oops, it looks like I forgot about this thread.
Lets start out with a little background info. The ECU has 2 modes, open loop and closed loop. Open loop is when you are at WOT, the engine is cold or the ECU sees a high enough load iirc. In open loop, the computer does not use the oxygen sensors. It also follows fuel/timing maps in the computer that are safe and richer than stoich (14.7:1) so as to produce maximum power and not detonate. Closed loop is when the motor is warm and is used for most situations. Closed loop utilizes all of the sensors to try and achieve 14.7:1 for best fuel economy and emissions. The timing is also more advanced in closed loop than open loop.
With the modular truck motors, the ECU in stock trim tries to stay in closed loop for too long when the motor is under load. It is the worst with the 6.8 V10 as they stay in closed loop for much longer than the 4.6 and 5.4. With a load on the truck and in closed loop, there will be too much timing and not enough fuel which means that the engine goes too lean and detonates. This causes the cylinder pressures to spike. These high cylinder pressures, in combination with the number of threads in the head and possibly poor install of the plugs causes the spark plug to eject itself from the head.
Now I am not saying that the number of threads is not the cause of the plugs popping. I am simply stating that it is not the main cause of the problem.
I can datalog with the predator in the Expedition and I can see when it goes in and out of closed loop. Towing a 9.5k enclosed travel trailer it jumped in and out of closed loop as I went up hills or encountered wind. This is good. I did have a tune in it though. A tune can change when it comes in and out of closed loop which greatly reduces the chances of the auto-ejecting spark plug.
Lets start out with a little background info. The ECU has 2 modes, open loop and closed loop. Open loop is when you are at WOT, the engine is cold or the ECU sees a high enough load iirc. In open loop, the computer does not use the oxygen sensors. It also follows fuel/timing maps in the computer that are safe and richer than stoich (14.7:1) so as to produce maximum power and not detonate. Closed loop is when the motor is warm and is used for most situations. Closed loop utilizes all of the sensors to try and achieve 14.7:1 for best fuel economy and emissions. The timing is also more advanced in closed loop than open loop.
With the modular truck motors, the ECU in stock trim tries to stay in closed loop for too long when the motor is under load. It is the worst with the 6.8 V10 as they stay in closed loop for much longer than the 4.6 and 5.4. With a load on the truck and in closed loop, there will be too much timing and not enough fuel which means that the engine goes too lean and detonates. This causes the cylinder pressures to spike. These high cylinder pressures, in combination with the number of threads in the head and possibly poor install of the plugs causes the spark plug to eject itself from the head.
Now I am not saying that the number of threads is not the cause of the plugs popping. I am simply stating that it is not the main cause of the problem.
I can datalog with the predator in the Expedition and I can see when it goes in and out of closed loop. Towing a 9.5k enclosed travel trailer it jumped in and out of closed loop as I went up hills or encountered wind. This is good. I did have a tune in it though. A tune can change when it comes in and out of closed loop which greatly reduces the chances of the auto-ejecting spark plug.
Junior User
Joined: Sep 2001
Posts: 56
Likes: 0
Update....
Update to my blown out plug...
The #3 cylinder plug blew out breaking the ignition coil with it....
My mechanic used a cylinder head repair kit made for the Expy.(insert goes in the head with special sized spark plug and boot)
Total for the fix: $250.00
The motor is a 5.4 in a 2001 Expy with 113,000 miles
Found this site also http://home.nycap.rr.com/tritonlemon/
Good stuff....
The #3 cylinder plug blew out breaking the ignition coil with it....
My mechanic used a cylinder head repair kit made for the Expy.(insert goes in the head with special sized spark plug and boot)
Total for the fix: $250.00
The motor is a 5.4 in a 2001 Expy with 113,000 miles
Found this site also http://home.nycap.rr.com/tritonlemon/
Good stuff....
Junior User
Joined: Sep 2001
Posts: 56
Likes: 0
Originally Posted by MisterCMK
Like I have posted before, all of the modular motors since 1992 have had the same design and haven't had a problem with popping plugs. The problem with the trucks lies in the tuning. The trucks try to stay in closed loop for too long when going WOT which causes the truck to be too lean and the cylinder pressures shoot up causing the plug to blow out. If you look at the spark plug that blows out, you will see that the gap is closed. This explains it.
How does a spark plug blow out from just starting the truck? I could understand if it was WOT like you said.....
I also looked at the plug and the electrode gap and color of the plug are fine, if that is what you are referring to.
Thanks for your help!
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