Joseph,

The plug in AFM disabling devices will work and will not mess with the OEM calibrations and will not do any harm to the system. However, they cannot be left in the diagnostic port for more than a few days or the battery will end up dead. They put a draw on the electrical system and do not have an auto shut down.

For the AFM hard part delete components, I would not recommend this since there are no control system modifications where the engine will still be commanding V4 where the spark advance will change even though the engine hydraulic actuators have been mechanically disabled. Also if there is a code set, the engine will revert to default cam position (even if it thinks it is in afm) minimum spark advance which could be as much as 15degress removed. Ouch on fuel economy. And the most important item is the camshaft must be replaced to do this right since the cam lobes are different between AFM cylinders and non-AFM cylinders. So its best to not mess with this kit unless the owner is willing to recalibrate with aftermarket tools (rarely done right), void their warranty and is ok with changing the camshaft. And besides, you will lose fuel economy by disabling AFM.

Jim

If you find it to be the AFM you can try https://www.summitracing.com/search/...96&keyword=AFM they are a bit costly.

The other alternative based on warranty and your willingness to tear down the top side of the engine is https://www.summitracing.com/search/...-based-engines

I once had a rumble similar to what you are describing. In my case it turned out to be the active noise canceling “feature” in the cab of the truck. The noise was coming from the sound system speakers. Very very difficult to find this problem.

I had installed a platform for the dog behind the front seats. It spanned the entire back seat area blocking the speakers in the doors from the microphones in the headliner. The noise canceling system under certain conditions would crank up the noise canceling sig Al to the speakers since the microphones could not sense it. A closed loop runaway audio loop.

cut some vent holes in the platform and all was well.

the audio amplifier was under the back seat. If you pull the power going to the amp it will doable the noise canceling. Then test.

Ken,

Look at your instrument panel on the fuel economy screen which will show if the engine is in V8 or V4. Make note if the engine is in V4 when you hear the rumble. Some models have a tuning valve in the exhaust system to mostly isolate this sound FYI. My truck will rarely run in V4 while towing our 2600RB but in downward slopes it will occasionally run in V4. Even in Tow Haul which I would have liked them to disable for towing. But that would make this feature a defeat device....another discussion.
Next time you hear the rumble sound, tip into the accelerator pedal just slightly and notice the V8/V4 box on your IP to see if the engine moves from V4 to V8 and if the rumble goes away. If it does, you can kill this feature by setting the truck into TAP mode on the shifter to a lower gear which most likely you are running most of the time anyway.

Let us know what you find.

Jim