Correct cranking fuel pressures
 

What would be the correct number to see in the rail for pressure during start up? I am seeing about 1100 when cranking. I am working to diag a no start on a 04 Cummins 325 hp engine when cold.

Thank you guys!

it should ramp up to 5k-6k pretty quick. it sounds like you may have inadequate low pressure fuel supply, or more likely, a high pressure leak. i would recommend checking lift pump pressure, then doing an injector return test. you can also measure the cp3 return while doing the injector return. guessing that you will find excessive injector return...

You need a minimum of 3500# rail pressure to start. If less, then check lift pump, rail relief valve, cross tubes for proper torque.

You can unplug the FCA, this will max the rail pressure to 25/26k and may allow it to start, but that just confirms it's a low rail pressure problem, not what is causing it. Do not operate with the FCA unplugged.

Lift pump was not pushing enough but after replacement it still takes a while to build pressure. Do you need the 9012 part (will be picking up the tester kit tonight) to check bleed off from injectors? It with out that in place and measuring the return flow I saw close to 3 cups in 40 seconds, which is not even close to the 180ml in one minute. But it seams you are supposed to bleed off some of the fuel using tool 9012 to get a good reading.

I don't have the specs in front of me, but now that it is running you can check idling volume. There is a spec for normal idling, and max rail pressure idling. I have seen some barely pass at normal idling pressure, and obviously fail at max rail pressure - so it is worth checking a max rail if in doubt. If you don't have a scan tool to command max pressure, you can just unplug the fca. However, you will have to clear the code.

You don't have to buy the special fitting - it is pretty easy to split the cp3 return from the injector return. You can use an extra banjo bolt to do this. You can drill and tap the head of the bolt and thread a barbed fitting into it (1/8in pipe by 1/4in barb works well), and weld the holes in the sides closed. When installed into the return on the back of the fuel filter housing it will direct the cp3 return straight through the banjo bolt out a hose attached to the barbed fitting. With a hose shoved over the return hard line at the quick-connect fitting, only the injector return will flow. The hoses are directed into separate containers, and injector and cp3 volumes can be measured at the same time.

Mike

Thank you for the help. It ended up being #4 injector.

Glad you got it figured out!