I got a call about a o4 that was reading no rail pressure and had a code for low rail pressure. The shop changed the sensor and it started reading pressure but would not start. With the aid of starting fluid they got it started but it runs very poorly and when you rev it up it misses and the rpms stay high for a long long time before it will come down to idle. I went to the shop and looked at the truck with the mechanic and watched the fuel pressure on start up and while it revs to the moon and dont see a issue so any ideas or thoughts would be great.

 

Sounds like an injector problem. Another guy on here has a post about a similar issue. Ate a cylinder too!

 

I did run a injector cut out test and that seemed fine as well

 

Did you do the bypass test? I think that's what it is called at least. It measures the amount of fuel being bypassed by each injector. The cylinder may be firing, but if the injector is leaking down it should show high egt's too. That would also be the cause of the high revs. Have any other guages?

 

I told him to undo the return line going to the tank and see how much is going back. I have never heard of bypass test, dont know how to do that one. All he is working with is a snap-on solus.