So I have posted in this section before about my trucks potential timing chain issues and was just curious about something. I'm not quite sure how to phrase this thought I have been having but will attempt anyway. I have a 03 4x4 4.0l v6, 140k.
I brought my truck over to my local mechanic and they told me that I would need the timing cassettes replaced that had gone bad and that was what was causing the rattle. My truck starts up rough and sometimes rattles, sometimes doesn't. Honestly it makes different noises all the time.

I have noticed that, If I start my truck and let the fuel pump kick in multiple times before I actually start it up, I noticed that it turns over much better and doesn't idle as rough and is not as frequent of the rattle I usually hear if I don't start it up that way. If it really is the timing chain, it definitely is the rear one.

But I had this crazy idea, if my truck starts up so much better when I let more pressure build up and that changes the rattle and idle. Could it be that it could just mean that something else is the issue and my truck is having a hard time building and keeping pressure, and maybe something in my exhaust is bad? Its interesting because its not always there (the rattle, it is more times than not) and when it idles rough, the idle sounds pretty hollow. But after I drive it for a while it doesn't have the rattle and idles fine.
I partly feel like if the timing chain stuff was bad that I would notice it more in I'm driving the truck.

I really dont know much about vehicles but have been learning alot bc the issues I've been having with this truck. Mostly trying to hope that the experienced mechanic is wrong and that I really don't have to spend thousands on replacing the cassettes or swapping the motor.

So if anyone is able to decipher this long winded, out of order question. I'd be interested in your thoughts.

 

The "rattle" is for sure one or both long timing chains guides are broken, yes noise can come and go but mostly come

The problem was the 2 tensioners on these long chains, the springs inside would weaken or break and wouldn't hold the chain tight when cranking engine, there was no noise when this was happening
Over time this would break one of the guides and thats the "rattle" noise, the now loose guide and chain
On these engines you should change the 2 long chain tensioners every 100k miles

The startup issue is unrelated, in the gas tank there is the fuel pump and fuel pressure regulator, these hold fuel pressure when key is off
One is not working, so fuel pressure is being lost when key is off
Yes, you can cycle key on and off a few times to build pressure back up
But good thing is, that if you change the fuel pump assembly you get a new pump and new fuel pressure regulator, so problem fixed

 

Is it possible that it could be a bad harmonic balancer causing the noise.