There are a few reasons that can cause a rich fuel mixture. First, high fuel pressure can be the cause. Also, a faulty engine coolant temperature sensor can also cause it.
Since you are hearing a pop (backfire), it sounds like you are getting spark. However, the plugs could be fouled if they are wet with gas.
Here is what I suggest: Remove a couple of the spark plugs and see if they are wet with fuel. If they are, then I want you to check for ignition spark to the plugs. Here is a link that explains how that is done:
If there is spark, I would next check the fuel pressure to confirm it isn't too high due to a faulty pressure regulator. Here is a link that shows in general how it's done:
Let me know what you find. Also, here is a link you may find of interest. It describes the most common causes of a backfire.
Let me know what you find. Also, let me know what engine is in the truck so I can check on fuel pressure specs.
Sunday, January 9th, 2022 AT 8:05 PM