i have a 04 dodge. when it is sitting there idaling it has a real bad rattle. but if you put a load on the motor like going down the road it goes away. i took it to the shop today but my guess is that its the rail pressure sensor. does anyone else have any ideas.

 

Any codes?
If the FCA (pressure regulator on pump) goes bad it can default to wide open and cause the rail pressure to be too high (23,000 psi)
That will cause a bad rattle at idle.
FCA's are real common to fail.

 

narrowed it down to either the regulator or the rail sensor

 

With the key ON engine OFF does the rail pressure sensor still read very high pressure?
If so I would suspect the rail sensor.

 

any word yet, mine has a noticible rattle at idle also. I was thinking to just check if the valves were out of spec. How would you check the rail pressure sensor? I don't have any engine codes.

 

good news i found it. bad news it was the fca (pressure regulator) those little things are exspensive. dodge sure are proud of those things. but it is fixed now and running good thanks guys

 

It's Bosch part, that's why it so pricey.
You're lucky you can buy the part separately. For the first few years you had to buy the whole CP3 pump to get the regulator! $$$$.$$
Glad you got it fixed!