Sporadic Misfire
02-07-2016, 01:29 PM
#1
Senior Member
Thread Starter
Join Date: Aug 2008
Location: Shakopee, Mn.
Posts: 187
Likes: 0
Received 0 Likes
on
0 Posts
Sporadic Misfire
2 weeks ago today I completed the intake manifold swap and passenger valve cover gasket replacement, new knock sensor and new temp sensor. Put in the recommended Motorcraft plugs at .054 gap. Left the boots, no tears and the boot rubber was supple and I reused the COP's. The old plugs looked great. I washed the truck on Wednesday afterwork and Thursday morning on the way to work the misfire started. The misfire is all over the rpm range and loads. NO CODES are being sent. I haven't pulled the plugs to look for a carbon trail and I have not done any of the misfire tests as of yet. No oil or coolant smell and the misfire is very sporadic at this point which is why I haven't done the work. Suggestions on other possible causes... Please advise
02-07-2016, 04:34 PM
#2
Senior Member
Sporadic. This isn't the action of a bad coil. Sporadic would be a bad connection IMO. Perhaps you removed a coil spring and attempted to reinstall it, resulting in intermittent loss of connection. Yea they can be a little tricky to get back on there right. You could easily pull them back off fishing the spring back through the boot.
Check #4, #7 & 8. The boot may actually fold once in contact with the plug mounting improperly.
Sporadic, the way I'm think of it should shoot you a DTC.
Well, try this. Accelerate normally from start under load, - drive the truck. At what MPH do you first notice it miss ? A bad coil during low grade misfire will usually miss under load at 45 mph right after the shift into OD. That's how you can differentiate the coil itself from another possible problem. Then we'll go from ther.
Check #4, #7 & 8. The boot may actually fold once in contact with the plug mounting improperly.
Sporadic, the way I'm think of it should shoot you a DTC.
Well, try this. Accelerate normally from start under load, - drive the truck. At what MPH do you first notice it miss ? A bad coil during low grade misfire will usually miss under load at 45 mph right after the shift into OD. That's how you can differentiate the coil itself from another possible problem. Then we'll go from ther.
02-07-2016, 09:37 PM
#3
Senior Member
Thread Starter
Join Date: Aug 2008
Location: Shakopee, Mn.
Posts: 187
Likes: 0
Received 0 Likes
on
0 Posts
As an example
I went to visit a friend today about a 30 minute drive. I started the truck and it was misfiring at idle and for some of the drive. Sometimes while cruising and sometimes under load during a pass. On the way home my truck ran smooth no misfires. When I was swapping parts I had trouble with the # 8 boot it didn't come out easy like the others and was the only 1 giving trouble going back in. I think I'll redo the boots and start with #8.
02-08-2016, 06:32 PM
#5
Senior Member
Thread Starter
Join Date: Aug 2008
Location: Shakopee, Mn.
Posts: 187
Likes: 0
Received 0 Likes
on
0 Posts
On the way to work the CEL started flashing and on the way home the CEL decided to stay on so I stopped at AutoZone and they pulled P0307 #7 and P0172 .
02-08-2016, 08:04 PM
#6
Senior Member