New to the site. I have a 2012 cummins 6.7 with p0087 code. I hooked a scanner up too it and it reads 18000 psi when the demand is 26000psi. I have an h&s xrt pro tuner with delete and fuel rail plug. Tuner is set at tow setting and has never been at high setting. What could be the problem?

 

Well I got my problem fixed. I put the stock relief valve back in and now no longer have p0087 code. I think that the h&s rail plug didn't completely seal and that caused my fuel presure to go down.