P1093, U1000 Codes & description of problem

97Cobra · 08-02-2007, 07:31 PM

Stock 2002 6.6 duramax:

First start of the day, every day, starts quick, easily and without a hitch. Every other start during the day seems to take forever sometimes not starting at all. Once started the truck runs perfectly no hesitation, studder, anything.

New fuel filter & batteries checked good under a load test. Also dealer checked the injectors, said to be doing great.

Have two current engine codes but no engine light.. wtf?

P1093 - Fuel rail pressure low during power enrichment??

U1000 - Loss of communication?? -> with what from what to what??

Its stock so it shouldn't be running out of fuel should it? Also like I said, it runs great, even under wot.

**ob_1jr** · 08-02-2007, 08:17 PM

Sounds like your fuel pressure regulator is weak. About the only way that you will know for sure is to have the dealer drive it around with the tech II attached to see when it pops the P1093. A good percentage of the time it is the fuel pressure regulator. Stock trucks shouldn't run out of fuel. Although, if it isn't running bad and cutting back power, I wouldn't worry about it. It could have just been a stored code that you had from before.

97Cobra · 08-03-2007, 04:08 AM

The dealer had it all day yesterday and said they couldn't figure it out for me to bring it back on monday..

I'm not worried about the way it runs, its the starting that scares me, I'm leaving on a trip this afternoon and I just don't want it to leave me stranded anywhere.

thanks for the help!

**ob_1jr** · 08-03-2007, 07:36 AM

Well, if they don't find anything, the next time it takes more than a few seconds to start, open the hood and just push on the primer button until it gets hard to push. See if that helps.

97Cobra · 08-03-2007, 11:30 AM

Did that, seemed to help some but not a lot. It seemed to occasionally get fuel and hit just for a second but not enough to crank. I gave it a very small shot of either and it fired right up and ran great. I'm stumped.

The fuel system has to be losing pressure beause if you start it back to back with just a second or two in between, it always starts but if you give it 10+ minuntes you can hang it up, its going to take a long time to start if it starts at all.

I'm going to hook a fuel pressure gauge to it and let it sit for a while and see what it does. I really don't know..

97Cobra · 08-07-2007, 05:41 PM

More details.. The truck seems to be much easer to crank after its been sitting for 2+ hours.

My question is what is different from the first start in the morning, the starts between long periods of time, and the short break starts?

Something with the short break starts is really messing me up!

Could the pump in the tank be heating up and not working completly right? Could the fuel be thinner and harder for a weak pump to pump the correct pressure? What is the correct pressure for the fitting on the front left side of the motor??

**ob_1jr** · 08-07-2007, 07:48 PM

There is no pump in the tank. You could be getting crud stuck to the screen on the pick-up. I found this description on alldatadiy.com:

FUEL SYSTEM DESCRIPTION
If the fuel supply system is not delivering enough fuel driveability could be greatly affected. If air is being drawn into the fuel injection system a Cranks But Will Not Run, or a Hard Start symptom could exist. If another diagnosis indicates, or if the fuel supply system is suspected of not delivering enough fuel or drawing air, the following systems should be checked:

Any air leaks or restrictions between the fuel injection pump and the fuel tank will seriously affect pump output.
Insufficient fuel in the fuel tank
Any loose fuel component connections
Any hoses and lines that are flattening when the engine is running, or have kinks that would restrict the flow of fuel

SUPPLY SYSTEM
The fuel flows through a pre-filter screen in the tank and to the engine through the fuel supply lines. There is no lift pump in the fuel tanks or on the frame.

The fuel passes through the base plate of the fuel injector control module (FICM) to cool the module. From the FICM the fuel flows to the fuel filter assembly, which combines a water separator, a prime pump and a filter element. Within the assembly, there is also a fuel heater. An integrated hand pump is used to prime the fuel system after changing the fuel filter or servicing the fuel system. The fuel injection pump at the front of the engine valley includes a fuel supply pump and a high-pressure pump. Fuel is drawn to the supply pump from the primary fuel tank by the supply pump and delivered to the high-pressure pump.

I uploaded the procedures to check for an air leak here: Fuel system troubleshooting

97Cobra · 08-08-2007, 02:40 PM

Great information, I'm 100% fresh when it comes to these duramax's.

I also began thinking it might be some sort of module or electrical device causing the problems, hence the hard starts when warm but it starting like new when cold. Is there anywhere I can find out what all electrical componets have to do with and control the injection of the fuel at start up?