Low power on my 2003 7.3 F350. The truck runs fine but I can tell it is low on power (seat of the pants). I figured it to be fuel related so changed fuel filter and oil with no change. When that didn't work I installed a fuel guage and this what I found. Key on no start fuel pressure 45 psi. Start truck the pressure will get up to 61psi. Under a load it will drop down to the low 30s. I have dropped the tank mixing chamber screens clean and so was the tank. Changed fuel pump and now under a load it drops to the high 30s. Does this sound like the fuel pressure regulator is leaking by and causing low pressure under a load? Truck is stock besides superchips 1705 programer.

 

You have either a restriction. Which, Air forced back through the Fuel Pump Feed line "may clear". You will know when you test it again. If it corrects the problem, you'll need to drop the tank and clean the screens on the mixing chamber. OR Your Fuel Pump is in need of replacing which I would put my money on.

Another way to evaluate the Pump is by the Amps it draws. Using a DVM and a Low Amp Clamp, you should see about 8-10 amps. Anything higher means its not spinning as fast as designed and it's worn.

As a suggestion, DO NOT drive the vehicle with Fuel Pressure Under Load lower than 42 psig. Injector damage can occur.

 

It's possible for the fuel pressure regulator to stick, but if it shows up to 61 at times I think we can infer it is fine. When mine stuck it went high.

Normal operating pressure should not go under 45 psi.

To eliminate the tank/screens as the problem remove the fuel line from the back of the pump and put on some hose leading to a container of fresh clean fuel. Put it in drive and do a brief brake stand to put some load on the motor. If the fuel pressure stays good the tank/screens need the Hutch mod. If pressure drops to 30s the problem is downstream.

What kind of pump did you put on it? Any fuel in the coolant degas bottle?

 

Replaced with factory bosch pump. The screens in the tank were fine inspected everything else while I was there. Nothing looked damaged or plugged. I like to try and keep it all factory but I might have to do the hutch mod.

 

Also once I hit crushing speed pressure comes back to right @ 60psi. Just drops on acceleration. So it is like the pump can't supply enough volume but can deliver the pressure.

 

Either the pump is defective or, you have restriction in the system.

Are you using an OEM Filter and Cap? Others often don't compress the Stand Pipe far enough.

Have you removed and inspected the Return Pressure Spring?

Have you checked for a Voltage Drop at the Pump? Anything lower than 12vdc increases amps and slows the pump causing damage.

You can place a pick up tube attached to the inlet side of the pump and into a Gallon of fresh fuel. Check it then and at 3,400 RPM for 1 minute while monitoring gauge. This will help determine the pump's health with a Voltage Drop test.

Have you checked your cooling system for Fuel Contamination? Most prevalent when cool.

Here are some additional tests you can perform:

Fuel Pressure Test:

Tools: Fuel Port Adaptor (M12 1.5) and Pressure Gauge 0-160 PSIG / DVOM

** Fuel Bowl Test Port Spec. 45 psig min See 8c. below

8b. Right Head:

a. Fuel Pressure at the right head Verify that fuel is in the tank and the pump is being powered.

b. Measure fuel pressure at the front of right cylinder head Road Test- engine at full load condition Spec. Measurement / Head 0-160 PSI /
WOT 45 PSIG min.

c. If fuel pressure fails low, go to step 8c.

*If pressure is above min. spec, go to step 8b.

d. Fuel Pressure at the left head Measure fuel pressure at the front of right cylinder head Road Test- engine at full load condition Spec.
Measurement / Head 0-160 PSI / WOT 45 PSIG min.

CAUTION: Secure hose away from turbo and exhaust if fuel pressure is below min. spec, replace left check valve if fuel pressure is above
Min. spec, * Go to step 9.

8c. Electric Fuel Pump

a. Measure Fuel at Fuel Bowl Test Port using Fuel Port Adaptor (M12 1.5) and Pressure Gauge 0-160 PSIG / DVOM Spec .45 psig WOT >42 psig

b. Measure at fuel outlet from electric fuel pump: Engines built since 1/1/98 or engine serial #661496 should be 51 ± 4.5 PSI @ idle.

c. Road Test- engine at full load condition 42 PSIG MINIMUM*

d. If fuel pressure fails low, go to step 8d.

e. If pressure is above min. spec, replace right check valve.

8d. Electric Fuel Pump Inlet Restriction

a. If fuel line is restricted above 6 Hg, check for: blockage between pump and fuel tank.

b. If fuel line is not restricted, inspect regulator valve condition and for debris, If OK replace pump

*Testing Procedures on all 7.3 DIT 1999.5-2003 F-250-F-550 Models*

 

I have been out of pocket for awhile. But this is what I have found. I do not have factory fuel bowl cap. I'm am going to order one and replace. There was no voltage drop on the pump. I did pull the fpr spring and that looks fine. The pump will fill a gallon jug in to 20 second key cycles so I feel the pump is putting out plenty. I am not sure about testing pressure at the heads? What is normal pressure drop at WOT on a tuned 7.3 with factory fuel system and injectors?

 

"The minimum pressure under throttle should not be less than 42 psig measured at the Fuel Bowls Fuel Discharge Port of the Fuel Bowl" (Factory Service Manual)........ So, let's say 45 psig since we can see that on the Gauge.

You said the pumps voltage did not drop. That's a bad sign. The pump should drop a % based on specifications.

These truck need volume, the only way to get it through the system is pressure. It appears you have the volume at the pump. You don't have it [pressure] at the Head side of the Bowl.

I would look in order:

Cap/Filter/Bowl/Return Spring

Fuel Line Restriction

Pump

Check Valves

 

I will get new cap and filter and rebuild the fpr and see where that gets me. I post my results after
Thanks,

 

This one is classic air-in-fuel. You say you dropped the tank to clean the screens, but you say nothing about dealing with those crappy quick-disconnect O-ring on the fuel line. They are bad enough after years of use, but messing with them and re-installing will actually make the situation worse. I don't suppose you left the tank near empty while testing the repair... this is a worse-case scenario.

Hook up a temporary fuel line directly from the pump inlet to a fuel can and see where your fuel pressure lands.

45 PSI Key On and 61 PSI Engine Running will also imply weak batteries. What is the voltage on your batteries when you first turn the key (Glow Plugs On)? If it's below 11 - 11.5 volts, you want to do something about this before winter.

 

I posted a thread earlier today with the same symptoms the OP had. I did the Hutch mod and did not do anything with my fuel line and am thinking I may be getting air in my fuel line. How difficult it it to replace the fuel line with the tank still in the truck or do I have to remove the tank to replace the lines?