Help: ?0090 – Rail pressure regulator

[vaddies]

GMC 5500, Duramax engine.
One day the engine just stopped and never get started again. Tried to diagnose the problem using BOSCH KTS, which hardly works and if only using Global OBD. It hangs over all the time and always shows mistake Р0090 – Rail pressure regulator. Upon start rail pressure immediately goes from 0 to 180 MPa, but car doesn't make any attempts to turn on the engine. We have checked the resistance of Rail pressure regulator as well as wires on it - no problem there.
There is an assumption that root cause is dead electronic control unit, BUT to make sure we have to check whether power is supplied to electronic control unit. Also, I know that there could be two electronic control units (ECM and PCM), and we don't know the status of connection between its. So, the need is:
- having these symptoms identify what could be a root cause OR
- share with me an engine management schema

ANY HELP IS HIGHLY APPRECIATED.

Cheers,
Vad

 

[MadMaxx61]

I don't have any thing to help but I am sure if we had more info like what year the Topkick is so we know what Duramax engine is in it and go from there.

 

[vaddies]

GMC C5500, engine produced in 2005. Is it what you are asking about? Cars like this are rarely presented in my country, so thats why I have no even all input information.

 

[JoshH]

I would suspect something with the fuel rail pressure sensor, but I'm not sure a bad fuel pressure sensor could cause that code. A P0090 code won't keep it from running, but low rail pressure will. When you try to start it, does it smoke any? Try unplugging the fuel pressure regulator and see what happens.

 

[vaddies]

Upon start low rail pressure immediately goes to 180Mpa, which means the problem is not in it. There is no smoke, as there is no control signal to nozzles. Also, nothing happens then fuel pressure regulator is disabled, which is obvious as error explanation is "circuit open" for rail pressure regulator. Electronic control unit does not manage the valve, or control unit is broken itself, or there is no power supply on it. Thats why I'm looking for a scheme.

 

[schulte]

I don't believe that at cranking RPM's you could be making 180Mpa. If that's what the ECM is getting for a signal, something is wrong.

In general, you've got three computers to deal with in the powertrain: engine control module, transmission control module, and if it's an '05 or older a FICM (fuel injector control module.

The ECM controls virtually everything on the engine including fuel pressure, allowing engine to start, RPM, etc. The FICM is effectively just a "driver" for the injectors. Rarely does a FICM or ECM go bad.

It's also rare that an a fuel rail pressure sensor goes bad.

In the fuel system you have a few major components. The CP3 is mounted in the valley of the engine, gear driven off the camshaft, and is what brings the fuel from 0psi supply (actually pulls from the tank by vacuum) up high pressure (up to 23-26kPsi depending on model).

On the CP3 you have a FPR (fuel pressure regulator). The FPR takes a PWM (pulse width modulated) signal from the ECM. The ECM generates this PWM signal for the FPR based on current engine RPM, current rail pressure, etc.

The ECM gets current rail pressure information from the rail pressure sensor (in an '05 LLY engine, this would be on the passenger side fuel rail about half way down in line with the high pressure feed lines).

There's also a FPRV (fuel pressure relief valve) on the back of one of the fuel rails. This opens up and "dumps" excess fuel if there's a pressure surge.

If your rail pressure sensor is bad, the ECM may think you have more rail pressure than you actually do. You need at lest 1,500-2,000psi to start the engine. If you have a bad rail pressure sensor, and the ECM thinks your rail has high enough pressure, it will close down the FPR on your CP3, which will mean you have no actual rail pressure.

Another thing to look at is the FPRV (fuel pressure relief valve). Generally they don't go bad, and if/when they do they usually only open up at higher pressures (not just dump at any pressure).

The first thing I would do is get a GM Tech-II or EFILive software to try to get a good idea of what kind of rail pressure you have at idle.

Unplugging your FPR from your CP3 is another way of diagnosing. If you have a bad rail pressure sensor, unplugging your FPR will prevent the ECM from regulating fuel flow into the CP3, which will max out your actual rail pressure.

You don't want to run the truck for long like this, because basically you'll be running at max rail pressure. But, if you unplug he wire that goes to the FPR on the CP3, and the truck starts up just fine, you know you've got an issue somewhere with the rail pressure sensor (or something else that's keeping you from holding rail pressure).

Someone correct me if I'm wrong, I just typed that off the top of my head and might have missed something...