Hi everyone - new guy here. I did a search and didn't find specific results, so forgive me if this is a duplicate.

I have an all-stock 2005 2500/5.9 auto with 38,000 miles. It sat for 7 months because I was on the west coast, and when I got back it would crank all day but not start.

There were no codes and plenty of fuel getting to the CP3. I disconnected the CP3 electrical connector and it started right up but ran roughly. Reconnect CP3 electrical connector and no start again.

I am under the impression that this means either a hung open injector or a bad pressure regulator. How do I diag this so I'm not throwing money at parts I don't need? I was a master tech at various dealerships before the days of HPCR but never worked on diesels. I can't take it back to the dealership (nor would I want to) because it has a Frybrid kit installed. Note that the Frybrid kit has never been turned on and the truck started up just fine with the kit installed before I left, so the kit is not the problem.

TIA for any help you can throw my way!

 

Check to see if your fuel pump is working! You can check it by turning the key to start and lesion to the pump if you do not hear it run it is no good===-Good luck

 

You unplugged the fca.Be careful running the truck when doing that.It makes the rail pressure go to max(24kpsi).That could be what caused the rough idle when it cranked.

You could have problems with the lift pump,fuel filter,fca,rail pressure sensor and relief valve.Changing the filter and verifying you have lift pump pressure would be a starting point.You can do a search on how to inspect the relief valve.The RP sensor and fca will need a DRB or Starscan to verify they are working properly.Good luck and keep us posted.

 

Try replacing the FCA. It sounds like it has stuck and not working correctly.

 

Lift pump works fine, I have plenty of pressure and volume at the IP intake connection. Fuel filter is new, and truck started and ran fine after filter was installed but before the truck sat for six months. System has been extensively bled. As mentioned, the truck will start right away and run (rough) with the FCA electrical connector disconnected but will not start at all with that connector installed.

I don't want to just throw parts at it, especially because it could be a bunch of different things, and money is tight.

Anyone have experience diagnosing these things?

 

When you are cranking the truck the ecm is sending 0 volts to the fca,essentially full fuel,same as if you have it disconnected.But when it fires it sends a predetermined voltage to maintain idle.Why it cranks with it disconnected is beyond my knowledge.Only a DRB or Starscan is going to be able to see what signal is not correct.We can all sit here and speculate what is happening but going to the dealer or a service shop with the right tools is going to get to the bottom of it,other than that you are going to be throwing parts at it.

One other part not mentioned is the cam position sensor.It is used for cranking only and then the timing duties switch to the input from the crank position sensor.But like already mentioned a DRB or Starscan is needed if you are not wanting to get into a guessing game.

 

The system is self bleeding, no reason to even worry about that.

If it starts with the FCA disconnected its one of 2 things, the FCA or the rail pressure is not high enough. The latter could be rail pressure relief or injectors or CP3. To troubleshoot your gonna need to see rail pressures and crank and run, flow test the injectors, and check th RP valve.