6.7 powerstroke high pressure fuel diagnostics - Ford Powerstroke Diesel Forum
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post #1 of 2 Old 05-18-2013, 05:58 AM Thread Starter
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6.7 powerstroke high pressure fuel diagnostics

Here is a quick list to check if you get a no start with fuel rail pressure below 1000 kpa.
Basically we want to check 5 components.
These trucks are the same as all Fords/Diesel as the want a minimum pressure in the rail before they will try to fire injectors.
The high pressure fuel is controlled by 2 regulators, the volume regulator on top the cp4 and the blow off valve pressure regulator on the rear left rail.
The regulator on the left rail functions so that during key on engine off and not cranking it is open allowing lift pump pressure to flood the fuel return. This is done because the piezo crystals are not strong enough to operate the injectors without a bit of return rail pressure. Once the engine is cranked the regulator on the back of the rail needs to seal up and stop leaking fuel.
The volume valve meter fuels before it enters the plungers and barrels in the cp4 pump. It have 4 slotted holes in a thin steel barrel that sits on a spring. The spring pushes the barrel to a position that will block fuel from entering the pump body when the regulator is off.
1. Check Low pressure fuel. This can be done with a scan tool looking at the low pressure switch, or the old fashioned way with a gauge.
A quick tip here. The typical failure with cp4 pump is a bad valve seat on the Intake non-return valve (suction valves). We have found that when an injector line is cracked open, and the key turned on to operate the lift pump a good cp4 the fuel will ooze out. In the case of failed suction valves the fuel will poor out and travels about 1.5 to 2 inches up.
2. Check the fuel rail pressure sensor circuit. This sensor is on the front of the left fuel rail. With 5 volts shorted to signal rail pressure will read 0, with the sensor unplugged rail pressure will be 227000 kpa. This doesn't check the mechanical function of the sensor you have to swap a known good one in. I would suggest a few more checks first.
3. Check the fuel regulator 2. The is a fuel line with a green plastic connector that is connected to the rear left rail and ties into the fuel return plumbing. Remove the line by pulling up on the bottom of the plastic press down connector. Do not break it, try taking one off an injector that you can see more clearly first to understand how to remove them as this connector needs to be done more by feel. Now kink the return side in your hand and watch the rail as a helper turns the key on, you should see a steady stream of fuel pour out of the fuel rail.The other way to do this would be a clear hose and a bottle and pinch off pliers or the ford block off plug in the return side of the line, that would be less messy. We are NOT on the high pressure side of the rail right now, but a totally stuck open regulator 2 could see higher fuel pressure so use CAUTION. Have an assistant crank the truck you should see the regulator shut and fuel completely stop dripping from the outlet on the rail. If fuel is still dripping verify the circuit and ecm control of the #2 regulator if that check replace the #2 regulator and retest.
4. Check the fuel volume regulator. This regulator is held in by 2 torx bit and slides into the top of the pump. By taking the intakes off to the turbo you will see it hiding behind the coolant crossover tube. With the key on you should be able to feel it buzz. If it isn't buzzing I would first check the circuit with a test light in place of the valve. Verify the circuit and ecm function if that check good remove the valve. On a clean workbench firmly press a torx screw driver in the end that is closest the pump. This is a small round washer use the torx in a twisting/prying motion to remove the washer. This is a delicate operation DO NOT SCAR THE WALL OF THE VALVE. If the wall is scored the barrel will not come out. One the washer is off remove the spring. Inside is a small barrel, tap the valve on the table and make sure the barrel moves. If the barrel is stuck this is the problem. Replace the valve and check fuel system for water and contaminants you may have big problems. Retest the system/ try and start the truck. Just to save everyone the trouble we have enlarged the holes in the barrel of the regulator to modify them. This has a minimal effect on the ability of the truck to hold rail under high injection duration. In our opinion only needed with larger plungers and barrels.
5. Now we are ready to spend some money. We have narrowed things down to a failed cp4. This is the time where I may just try a new fuel rail pressure sensor. Its allot easier than changing a cp4 but still cost around 350 dollars. If you are luck a buddy will have one and let you give it a shot.
TO replace the cp4 remove the fan, the bracket that holds the fan and the vacuum pump. Than turn the engine to tdc and line the single mark on the cp4 up with the 2 marks on cam. Pull the coolant crossover off and turbo replace cp4 and put it all back together. I would suggest taking the four bolts out of the plates on top the cyliders of the cp4 and looking at it. There is a spring in there so it is under some pressure. You can hold it with your hand as you take the last bolt out. If everything goes flying here is a picture.

You want to look at the barrels and tungsten plungers, if these are scored we know where the metal went. Pull all the rails and lines clean them or replace them. Have all 8 injectors tested/replaced. If the barrels look good than it is just a typical suction valve failure. You need a new pump the suction valves are impossible to get.
The fuel system is self bleeding. Just turn the key on for 30 seconds at a time 3 or 4 cycles and you should be good to go.
I hope this helps.
Please post any questions or revisions.
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post #2 of 2 Old 12-17-2013, 01:43 PM
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Can you clear out your PM box?

Any chance that you would know what the torque spec is for the mounting nuts and the timing gear nut? I have trying to find it and am not able to come up with it. Any help is appreciated. Thanks
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