2003 F-250. Fuel pressure just started fluctuating randomly. No codes. No smoke. It will begin to skip if it stays around 10psi for 30 seconds, otherwise you would never know without the gauge. Replaced both filters about a month ago with motorcrafts. Any idea what this could be or how to start troubleshooting?

Video to show what it’s doing.

https://youtu.be/j648bALZu1Q

 

Fuel pressure below 45 psig in a 6.0L will damage injectors.

Low (and even fluctuating) pressure can come from a bad regulator, a bad fuel pump, clogged suction screen in the fuel tank, clogged filters, etc.

Do you drain the water every time you replace the filters? There is a drain plug for it and just replacing the filter does not drain that reservoir.

Could be an issue with the gauge. I know a few folks that had issues with their glow shift fuel pressure gauge.

Is your fuel system stock (ie pump, regulator, suction line in tank)?

To avoid just throwing money at it, you are going to need to do some investigation work.

Will the pressure fluctuate at idle, or stay low at idle? If so, you can rig up a line to feed the pump out of a bucket of fuel to see if that fixes it. Seems that these fuel tank pick-up screens are failing/breaking ........ now that they have some age on them. The plastic can get stuck in the lines. Also, any trash in the tank (fuel additive bottle cap liners particularly) can periodically blind off the suction screen.

If you have trash in the tank, or if the fuel pick-up screen/tube has failed, then I would think hard about installing a sump and feeding the pump from the sump. If you don't want a sump, then you either would have to drop the tank or lift the bed to remove the fuel level sensor and pick-up tube/screen. Again - this is if you suspect that you have an issue inside the tank.

My fuel pump failed at about 200k miles. On another forum, there is a poll about fuel pump failures. Seems like 200k out of them is doing pretty good. You might also just have trash/algae/sludge in the HFCM itself. You can pull the manifold cover and inspect. You can just replace the fuel pump by itself to save money, but there are components in the HFCM that wear out over time. The HFCM (which comes with a pump) is quite a bit more than the pump itself. Lastly, has the fuel pressure regulator ever been upgraded? If not, you may want to start there. It usually needs to be done on ALL 6.0's. International/Ford have their "blue spring" upgrade kit for that.

If you are interested in a new fuel pump only, I only recommend the Racor pump (they are the OEM fuel pump supplier). I can post a link if/when you want it.

 

I installed the blue spring today. I did see fuel pressure reach 78psi afterwards. However, that was short lived and the pressure started dropping after a few minutes of idle. One thing I've noticed, which I don't recall seeing in the past, is that when I turn the key on to prime the pump, fuel pressure goes up VERY slowly. Once the pump stops priming, it immediately starts dropping pressure. Shouldn't the truck hold pressure after its been primed? My "load %" is very high at idle as well, between 70-90%. It has a roughish idle as well. This was actually the first symptom that I observed. After a few minutes of idling, load values would be around 40% and the truck would run great.
Does this tell you anything?
To answer your other questions, I do drain the water. The gauge is not faulty because when the gauge dips down to 10-20psi, it runs like crap. As far as I know the entire fuel system is stock, aside from the blue spring mod that I installed today. Fuel pressure does fluctuate at idle

 

There is a timer of the fuel pump operation, so after 20 or so seconds of being on (without the engine running), the pump will shut off. The fuel pressure will drop quickly when the pump shuts off.

Could be something going on with the fuel pump suction line screen as stated above. You can test that as described above. Might also be worth removing the HFCM manifold cover to inspect it.

Not to be a broken record, but low pressure will kill injectors. Don't push it ........

 

I appreciate the warning! I have not driven the truck since making this post. Only idle time since replacing the spring.

I did remove the HFCM yesterday and there was a lot of gunk in there. Pictures attached. Looks like I need to drop the tank and see what’s going on?

 

Yeah, I would drop the tank.

You probably should blow air backwards through the pump suction line also.

 

I blew air into the line yesterday, gas cap off at first, and heard rattling around in the tank. Then I put the gas cap back on and blew air back in. Once I removed my air tool, fuel began coming out of the line. I thought it was unclogged at that time and hooked the lines back up. But I still couldnt build any fuel pressure. Lift pump was replaced yesterday as well. Ill be checkout of the tank tomorrow. I went ahead and ordered a screen.

 

Fixed! The screen in the tank had broken into a million of pieces. New screen and she’s back on the road! Thanks for the help!