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Daniel Wilson
Daniel Wilson,
Category: Medium and Heavy Trucks
Satisfied Customers: 4373
Experience:  Owner at DJ Wilson
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2006 C7 low side fuel pressure dropping off under load. Code

Customer Question

2006 C7 low side fuel pressure dropping off under load. Code 94-1
Submitted: 6 months ago.
Category: Medium and Heavy Trucks
Expert:  Bradley Martin replied 6 months ago.

Do you have the serial number for the engine?

Customer: replied 6 months ago.
Let me get it. WAX23226
Expert:  Bradley Martin replied 6 months ago.

That code is a low fuel pressure warning do you want the troubleshooting guide for that issue

Expert:  Bradley Martin replied 6 months ago.

Here is troubleshooting for that code

Customer: replied 6 months ago.
Let me get it. WAX23226
I read over the diag tree for the code and we have verified sensor pressure reading with mechanical gauge while driving. Actual pressure matches sensor reading.
Customer: replied 6 months ago.
I read over the diag tree you sent. We have already followed that to its conclusion without resolution of the problem.
Expert:  Bradley Martin replied 6 months ago.

Do you know what the fuel system pressure is?

Expert:  Bradley Martin replied 6 months ago.

Do you know what the oil pressure is and does it fall off when this happens?

Customer: replied 6 months ago.
Oil pressure remains steady at 55 psi. Low side fuel pressure is 65 psi at idle and will drop to 5 psi under load.
Expert:  Bradley Martin replied 6 months ago.

Let me opt out see if someone else has an idea on this.

Expert:  Daniel Wilson replied 6 months ago.

Hi my name is***** will be glad to help. If you are dropping pressure under a load and there are no leaks of restrictions your problem is either a faulty pressure regulator or fuel transfer pump. Its common for either of these to cause low fuel pressure. Let me know

Customer: replied 6 months ago.
Hi Dan. As I believe I stated in my original post we have in fact replaced the transfer pump -twice- and installed a new regulator. This is not your average problem. That is why I am here.
Expert:  Daniel Wilson replied 6 months ago.

Thanks for the update. Tee into the fuel rail with regulated shop air and check for leaks at the injectors or injector o rings allowing fuel to bypass. if all external fuel system components have already been checked and verified okay. Let me know

Expert:  Daniel Wilson replied 6 months ago.

You will likely find a mechanically faulty injector or an injector o ring problem. Look for worn injector cups if the injectors are removed for reseal and be sure to clean the cups well and inspect.

Customer: replied 6 months ago.
Ok that's good advice Daniel. Thanks. I told one of my techs that worked on it that the problem had to be in the head doing exactly what you said -bypassing fuel- either through an injector or somehow within the head itself. We are not 'making' oil so we know its not leaking fuel into engine. Nor are we getting any fuel into the coolant. Somehow, some way the fuel is just slowly drifting off when demand is highest. The shop air test should reveal the problem and should have insisted that the test be done. At this stage, however, we have turned the truck back to the customer and they are using it with the understanding that they will not be able to make full power for sustained hard pulls. I will contact them tomorrow and get the truck back into the shop for that test. I have no problem paying you for your service should this find the solution...but give me a few days to get the truck back if you would. Thanks, Don
Expert:  Daniel Wilson replied 6 months ago.

Pleasure to help Don. Let me know

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