I have a 95 F150 with 145K miles w/a 4.9 and a 5 speed. when I start it cold, I have what could only be described as a "Open exhaust sound." Meaning that the exhaust is noticeably louder, and when I get out of the throttle, it has a popping burning off type sound to it. It will be like this for 2-3 minutes, and then, like you flip a switch, the exhaust goes quiet, (I have full tail pipes out the back.) and the truck runs/idles better.

The thing is, intermittently, the loud exhaust note will come back, (most noticeable at idle) and the exhaust will pop again when you let off the throttle... and then go quiet again... etc etc etc....

I am curious, is the temp sensor switch for the PCM going bad, and opening/closing the loop for the O2 sensor? or can the EGR cause something like this? I hope it is not the PCM, (I don't think it is) I replaced the PCM months ago because it stopped powering the fuel pumps... and I remember it doing this before it went bad.

I also replaced the fuel injectors last year, because after 24 years, they started spitting fuel, and leaking in to the cylinders... and recently the Cat too because of its age, and the injector issue before that.

There are no check engine lights.

I am just looking for insight, I want to resolve this, and do not want to just throw parts at it.

 

Really just sounds like an exhaust leak that seals up as the engine warms and expands. Try to pinpoint the location when it's cold at startup. You've got a few minutes that you can put your hand on the exhaust to feel for leaks.

 

that how it sounds coming out the tail pipes, from the back bumper.

 

Nothing the EEC does will have a significant effect on the exhaust note. This is the best way to find an exhaust leak:


(phone app link)

The cats do not age, and shouldn't be replaced simply for age or miles. Mine have nearly a million miles, and still work. Yours could have been damaged by the engine running rich, but I've never actually found a bad fuel injector.