CAT 930H Low fuel rail pressure

[rev16.11invoice]

CAT ET is throwing a code for "low fuel rail pressure" (~2700 hrs on loader)

I have swapped the fuel pressure relief valve with a known good one from my second unit and problem continues.
I do not see any signs of leakage/ crushed lines and fuel filters have been replaced.
The lift pump is a mechanical type and I have replaced it.

Pressure is typically 6000-8000 psi until wide open throttle (WOT) and will go as high as 17900 psi under load

Historically when the problem occurred the loader would die and at best limp off the road. This began in August and has been intermittent. It is now more or less all the time and the loader cannot do work.

Today (-20C) in gears 1-2 the loader operated fine and could maintain WOT at top speed @ ~8000 psi
However in 3-4th at WOT pressure would drop as low as 1300 psi and become erratic (2000, 3200, 5000, 7000 psi...) and the loader would bog and once again show the "low fuel rail pressure" fault.

The fuel pump has a computer controlled solenoid that will either close or open to increase pressure at the rail. The injectors do have a "leakoff" port and in theory could bypass fuel were they to fail.

I can post IATs and ECTs and any other sensor data under varying load conditions if you think this may help direct me, but I believe the senors values are correct and do not suspect the values they are providing the ECU...

 

[rev16.11invoice]

Here is an update:

I drained the tank and the fuel appeared to me fine. Also removed the float/sender assembly and viewed the inside of the tank. There was nothing in there that wasn't fuel.

The return line has a fuel cooler/rad and it has no obstructions.

Now the tank did seem to have a lot of vacuum pressure in it when I pulled the feed line from the tank to the electric priming pump...

I guess I'm kind of stuck beyond adding a vent or breather to the tank... The fuel cap should provide that function and I cant see why it wouldn't be.

Any suggestions?

 

[partsandservice]

I have yet to deal with a low rail code on a cat engine. Cummins fpt and John Deere I have. Most of the time in my experience a low rail code is the result of fuel supply issue, which seems to be something you are looking into. The easiest way to tell if it is a supply side issue or pressure side leakage is to shut the machine down when it codes and bogs out , then pull the fuel filters, if they are not full then you have a supply side issue and vice versa. Check any 90 degree fittings for obstruction on supply side. On the pressure side you have the rail relief, hpfp and injectors. Which injector can be an issue to determine. There should be a fuel return line from the injectors,. There should be basically no fuel leakage. If you remove the return line and operate and you have return fuel coming from the injectors then one or more of them is leaking off the rail pressure.