Originally Posted by zr2yz125
What does the rail pressure need to be start the truck?
It takes about 2500 PSI rail pressure for the injectors to deliver fuel and the engine to start.
That condition is usually caused by leaky injectors, that will not build up the rail pressure to fire the injectors. The reason it starts cold OK, is the fuel is more dense, tolerances aretighter, and does not leak as much.
Excessive leakage from the injectors usually results in a starting issue, which could occur hot or cold, but usually occurs hot because the fuel is thinner when hot. However, excessive leakage from the injectors can also cause a DTC P0087, P0093 or a P1093 to set. When using the scan tool to increase rail pressure at idle, if you can’t get to 21,000 PSI then the injectors are usually bad.
You can also use balance rates to help determine if you have any bad injectors. If an injector is leaking excessively into the return the balance rates are often at the edge of specification. Injectors that have a poor cylinder power contribution or a noise or smoke change when canceled will also need to be replaced and are likely to cause low rail pressure during cranking.
Balance Rates, when checked hot in drive after a hard test drive, should indicate bad injectors. Any injectors that are more than +/- 6 are a possible cause for rough run.
You can check the fuel return rate by removing the rail return line on each rail, and measure the amount of fuel in 15 min of cranking.
Engine at normal operating temperature, 181-189 deg. F.
Remove return hoses from one bank of injectors.
Use adapters to run hoses off of injector returns in to individual graduated containers.
Run engine until fuel flows from all four injector return hoses. Then with the engine at idle, command rail pressure to 17,400 psi with the scan tool. Place the hoses in the graduated containers for 30 seconds.
Turn off ignition and record measurements.
Repeat above steps on the other bank of injectors.
Add up all recorded measurements to determine total injector return volume. If the return volume is less than 144 ml for all 8 injectors, refer to the high pressure pump test. If the return volume is greater than 72 ml per bank, replace any individual injector with return volume greater than 18 ml.
What are your balance rates?
Google (Duramax lly hot start problem) lots of pointers.