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Old 08-27-2010, 09:52 AM
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More Power More Power is offline
Join Date: Feb 2000
Location: Big Sky Country
Posts: 10,506

Thanks for posting your problem and apparent cure!

For those not well versed in what the diagnostic trouble code P0093 is, the book says "Fuel System Large Leak Detected (2001 model year)". The description doesn't tell the whole story or indicate what else may be causing the problem.

In short, this code indicates that the "commanded" and "actual" fuel rail pressures are outside a window of acceptability (the computer really has no way of knowing whether a leak exists). The ECM commands a particular rail pressure, depending on load, accelerator pedal position and other inputs, then commands the Fuel Pressure Regulator (FPR) and high-pressure pump to deliver that rail pressure. Ordinarily, the system will respond and generate those pressures.

There are a variety of causes of a P0093 trouble code, it could be that the injectors are worn and their internal clearances are allowing too much fuel to leak past the internal components of the injector(s). The FPR and high-pressure pump can't generate enough pressure/flow to compensate.

This code could also be the result of a faulty rail pressure relief valve, which leaks fuel pressure back into the fuel return line faster than it can be generated. The fuel pressure sensor could be at fault, as could the FPR or the high-pressure pump itself.

There is an injector fuel return test outlined in the service manual - using a set of four graduated cylinders, which are used to measure injector fuel return flow for one bank of injectors at a time. I doubt many dealer techs do this, but the test is available for those who want to confirm whether the injectors are the problem.

The window of acceptable pressures could also be so narrow that some trucks have a hard time staying within that narrow window of acceptable rail pressures. The 2001 trucks were the first to get a high-pressure fuel injection system like this. Variability in trucks, engines, fuel systems produce variability in setting codes.

We know that within the first year of production, GM widened the vehicle speed window when using cruise control because of driver complaints. I suspect there may be other areas of vehicle programming that needed some fine tuning as well. While we haven't heard the recommendation lately, during the first few years of Duramax production, GM recommended updating the ECM programming whenever the vehicle was returned to the dealer for service. I've had my 2001 ECM programming updated a couple of times. I wonder if maverick2's truck was recently updated by the dealership for this trouble code?

Always change your truck's fuel filter when a P0093 or any other rail pressure codes appear. Check your fuel tank cap for excessive vacuum. A faulty pressure/vacuum relief valve in the cap could add to the possibility of this trouble code. These diesel caps should vent at 2-psi positive pressure or 1" of vacuum.

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