How to check low pressure fuel pressure

Fordracer · July 11, 2012

I have a 6.7 with codes P228F (Fuel Pressure Regulator 1 Exceeded Learning Limits - Too Low) and P127A (Aborted KOER - Fuel Pressure Failure). Even though the PPT doesn't ask to check LP fuel pressure the hotline said to check it as that is usually the cause of these codes. This truck has passed all the PPT M tests and the codes come back after the customer drives it a few days.

Has anyone found a way to check the low pressure fuel pressure? There is no procedure in the PCED.

This truck has 18,000 miles on it and the original fuel filters. I would like to show it has low pressure so the customer has to pay diag along with replacing the filters.

Keith Browning · July 11, 2012

Pinpoint Test MA3 : CHECK THE LOW PRESSURE FUEL SYSTEM PRESSURE AFTER THE SECONDARY FUEL FILTER

NOTE: The FP will run for 30 seconds then shut off at ignition ON, engine OFF.

[*]Ignition OFF.

[*]Connect the low pressure fuel supply line to the secondary fuel filter.

[*]Disconnect the injection pump fuel supply tube from the fuel filter to fuel injection pump supply tube quick connect coupling.

[*]Install the Fuel Line Adapter 310-159 or equivalent and the DSL ENG Pressure Test Kit 014-00761 or equivalent to the fuel filter to fuel injection pump supply tube quick connect coupling at the fuel injection pump supply tube.

For vehicles that start,

[*]Road test the vehicle while accelerating under load while monitoring the fuel pressure gauge.

For vehicles that do not start,

[*]Ignition ON, engine OFF.

[*]Access the PCM and control the FPL_CMD (MODE) PID.

[*]Command the FP ON.

Is the low pressure fuel system pressure greater than 379 kPa (55 psi)?

Brad Clayton · July 11, 2012

This truck had a fuel pump that was on it's way out.

Pressure reading after new fuel pump installed.

Keith Browning · July 11, 2012

And there we have it! Posted Image

Brad Clayton · July 11, 2012

Fordracer · July 11, 2012

Thanks Keith and Brad. As always great pics Brad.

So to find diag procedures do we have to scour the PPTs to find them? Under section 4 Diag procedures all they have is checking for clean fuel.

The pressure is 88 psi at idle and 82 under a load. Seems a little high. I guess I'll call the hotline and see what they think I should do next. After performing PPT M it says nothing is wrong.

lmorris · July 11, 2012

Not high, average output from the low pressure pump should be around 75 PSI, from what I got during training. I would say your low pressure system is okay.

Fordracer · July 11, 2012

The hotline said it shouldn't be above 75 psi and a restricted secondary filter might cause it. I replaced the filters and the primary filter cup was covered with a brown mud like substance. If I can figure out how to post a picture I'll post one. Now my presure is 68 psi. We are going to see if the customer will let us pull the tank and see what's inside. This is an indian reservation truck and they aren't to easy on them and I don't think they have any paved roads and most of them don't even have gravel on them.

Fordracer · July 14, 2012

Here are the pictures of the primary filter housing and the inside of the fuel tank

I thought that there was supossed to be a warning come on when the filters are dirty and need to be changed. I guess we can't count on that if a plugged secondary filter will make the pressure to high and the warning won't come on because it sees plenty of pressure. This truck still had the original filters with 18,000 miles and 733 hours.

As you can see by the picture the tank wasn't very dirty so they must of got a bad batch of fuel and already ran it through. I guess we will see if any other issues show up later.

Keith Browning · July 14, 2012

Looks like a steel aft-axle tank. I see the crap on the bottom of the tank that looks like granulated rust... run your hand along the top surface of the tank through the sender opening. Tell me what you feel. If it is anything but smooth, use a mirror to inspect. When these tanks rust it is ALWAYS the upper surfaces of the inside of the tank.

Fordracer · July 15, 2012

The truck is already gone. I didn't know they usually rust on the top inside of the tank. This stuff was more like a powder not coarse like the rust I've seen but we don't have any where near the rust problems you do in your part of the country or like in Canada.

A while back these guys stopped using the gas station on the reservation because of fuel problems so now they store their own fuel in above ground tanks. I can see them leaving the cap off the tanks and with all the dirt roads and the drought we've been having with all the dust blowing around it's probaly dirt. Around here it would probably take alot longer than a year for a tank to start rusting.