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I could use some input guys. 05 F150 with the 5.4 that keeps throwing P0340/P0344 cam sensor codes. Using the Ford pinpoint tests, I have 4.5 volts on the signal return lines, which the tests indicate a short to power. Just to see, I made a bridge from the PCM plug to the sensor (cutting the factory wire to isolate it) and that sensor started working but I had a bunch of new codes. I realize that a bunch of other sensors share that particular wire.
I cannot find the common short. do you know of any other way to bridge that sensor? I am assuming that I cannot direct ground it. The truck is running great as it is but I can’t go thru emissions as-is
As you've discovered - there are a number of sensors that use the common 'signal return' with CPS sensors, including Oil Temperature Sending Unit, Fuel Rail Pressure Temperature Sensor, Power Steering Pressure sensor, Mass Air Flow Intake Air Temp sensor, Oxygen Sensor B1S1 to mention a few. So - NO - you cannot just cut that wire and bridge CPS sensor to the PCM. The PCM multiplexes multiple sensor readings in by 'polling' them.
The P0340 / P0344 code descriptions are the worst written 'diagnostic description' in the book!!!! - and, because of the above, it sends everybody chasing the rabbit trail you're going down.
A more accurate description for P0340 / P0344 is: "During the first few seconds of cranking, the PCM polled the CPS sensor and did not 'SEE' the phaser's fifth finger pass the sensor while attempting to verify TDC on Cylinder One to establish proper profile ignition pickup (PIP) for timing and firing sequence."
That could be caused by electrical issues. Hence the trouble shooting suggestions of circuit problems, low battery, bad starter etc. But the descriptions do not mention possible (AND MORE COMMONLY) mechanical reasons.
To understand mechanical causes of P0340 / P0344, one must consider Phaser design and VVT operational design. Internally the Phasers have a spring loaded locking pin that _SHOULD_ lock the phaser at base "ZERO RETARD" position on shutdown. By design, the PCM commands ZERO retard anytime RPM falls below 800 and/or engine load drops below 25%. It does this by removing all duty cycle pulses from the VCT Solenoids. This _SHOULD_ route 100% available oil flow / pressure into advance chambers of phaser and _SHOULD_ send it to base Zero Retard ('or full advance depending on how you look at it). This condition _SHOULD_ always work as RPMs decline down toward idle. At idle, (or shutdown) oil pressure declines below the magic level that _SHOULD_ cause the spring to push the locking pin into place - locking the phaser down at base (Zero degrees retard). NOW - everything is set up for the subsequent startup. BUT, what if one or more of the above "_should_" conditions didn't work???? Think about it.
NOTE: The phaser fingers are connected to the moveable front 1/2 of the phaser which connects directly to the Camshaft. At 'base zero retard', the 5th finger points at the phaser timing mark. Thus detecting the 5th finger at the CPS sensor indicates TDC of #1 (and #5 Bank2) on compression stroke.
ON StARTUP - during the first few seconds, there is no oil pressure to hold phaser internals at base timing. "IF THE PHASER IS NOT LOCKED in base timing position as it _SHOULD_ be, valve spring / valve train drag will 'DRAG' camshaft toward 'retard' position - as much as 32-35 degrees. That moves the 5th phaser finger way behind ('retarded') from the phaser timing mark. THUS, when the PCM 'polls' the CPS sensor (during the appropriate time window for TDC #1 to occur), it does NOT see the phaser finger and sets P0340 / P0344 as appropriate.
These two codes are 'sticky' and once set the CEL stays on - until the condition has not re-occurred for two or three drive cycles. Thus - it can be a relatively intermittent condition appearing to come and go. And the phaser may work just fine otherwise except for locking down right. This would give the sense that the engine runs just fine otherwise. But a number of things can be in early stages of developing.
For all these reasons - I believe your problem is most likely 'mechanical' and not 'electrical'. Especially if your truck in in the live / mileage phase where timing problems can begin to appear.
Sorry for the long post. Hope something here will help.
Excellent description of the mechanical portion of the VCT system
My dad just sent this to me. You're definitely a "guru" like your title suggests. This is the best mechanical portion of the VCT description for the 5.4 on the Internet. The system is very difficult to troubleshoot without a proper understanding. So thank you for spending the time writing it.
Any chance you can explain the electrical portion?
In this first image, left side is bank 1, right side is bank 2. Top captures are advance desired percentages, middle are advanced error, bottom are actual advance percentages. The top left (bank 1, desired %) shows a spike in the middle. This is going from idle (before spike) to in gear with a momentary acceleration with foot on the brake (seen at spike). When the error is displayed in the capture, the idle is extremely rough. We are confused as to the opposite mirror image of the errors (squiggly lines) between bank 1 and bank 2 under the advanced error capture (middle images).
2008 F150 5.4 rough idle signal capture
In this second image, truck is placed back into neutral, RPMs are accelerated to 3000-3500 until the engine is running smoother, then reduced to idle and the idle is normal.
2008 F150 5.4 clearing rough idle with acceleration in neutral
This only happens after the engine is hot AND has either idled for about 15min (after reaching operating temperature) or driven for about 5 miles (after reaching operating temperature). This is consistent and repeatable.
This last image shows the minimum oil pressure when engine oil is at operating temperature AND after it has reached the point where the problem occurs. In gear, at idle.
2008 F150 5.4 engine oil temperature, HOT (operating temperature + idle or 5miles), in gear, at idle.
And explanation or help would be greatly appreciated.
Originally Posted by F150Torqued
As you've discovered - there are a number of sensors that use the common 'signal return' with CPS sensors, including Oil Temperature Sending Unit, Fuel Rail Pressure Temperature Sensor, Power Steering Pressure sensor, Mass Air Flow Intake Air Temp sensor, Oxygen Sensor B1S1 to mention a few. So - NO - you cannot just cut that wire and bridge CPS sensor to the PCM. The PCM multiplexes multiple sensor readings in by 'polling' them. The P0340 / P0344 code descriptions are the worst written 'diagnostic description' in the book!!!! - and, because of the above, it sends everybody chasing the rabbit trail you're going down. A more accurate description for P0340 / P0344 is: "During the first few seconds of cranking, the PCM polled the CPS sensor and did not 'SEE' the phaser's fifth finger pass the sensor while attempting to verify TDC on Cylinder One to establish proper profile ignition pickup (PIP) for timing and firing sequence." That could be caused by electrical issues. Hence the trouble shooting suggestions of circuit problems, low battery, bad starter etc. But the descriptions do not mention possible (AND MORE COMMONLY) mechanical reasons. To understand mechanical causes of P0340 / P0344, one must consider Phaser design and VVT operational design. Internally the Phasers have a spring loaded locking pin that _SHOULD_ lock the phaser at base "ZERO RETARD" position on shutdown. By design, the PCM commands ZERO retard anytime RPM falls below 800 and/or engine load drops below 25%. It does this by removing all duty cycle pulses from the VCT Solenoids. This _SHOULD_ route 100% available oil flow / pressure into advance chambers of phaser and _SHOULD_ send it to base Zero Retard ('or full advance depending on how you look at it). This condition _SHOULD_ always work as RPMs decline down toward idle. At idle, (or shutdown) oil pressure declines below the magic level that _SHOULD_ cause the spring to push the locking pin into place - locking the phaser down at base (Zero degrees retard). NOW - everything is set up for the subsequent startup. BUT, what if one or more of the above "_should_" conditions didn't work???? Think about it. NOTE: The phaser fingers are connected to the moveable front 1/2 of the phaser which connects directly to the Camshaft. At 'base zero retard', the 5th finger points at the phaser timing mark. Thus detecting the 5th finger at the CPS sensor indicates TDC of #1 (and #5 Bank2) on compression stroke. ON StARTUP - during the first few seconds, there is no oil pressure to hold phaser internals at base timing. "IF THE PHASER IS NOT LOCKED in base timing position as it _SHOULD_ be, valve spring / valve train drag will 'DRAG' camshaft toward 'retard' position - as much as 32-35 degrees. That moves the 5th phaser finger way behind ('retarded') from the phaser timing mark. THUS, when the PCM 'polls' the CPS sensor (during the appropriate time window for TDC #1 to occur), it does NOT see the phaser finger and sets P0340 / P0344 as appropriate. These two codes are 'sticky' and once set the CEL stays on - until the condition has not re-occurred for two or three drive cycles. Thus - it can be a relatively intermittent condition appearing to come and go. And the phaser may work just fine otherwise except for locking down right. This would give the sense that the engine runs just fine otherwise. But a number of things can be in early stages of developing. For all these reasons - I believe your problem is most likely 'mechanical' and not 'electrical'. Especially if your truck in in the live / mileage phase where timing problems can begin to appear. Sorry for the long post. Hope something here will help.
Last edited by Scoop-n-Pilchard; Mar 14, 2025 at 01:29 PM.
You can try the VCT solenoids in my signature for that concern but it probably has too low oil pressure at idle. That 20 psi is right at the filter before the mains and rods get their share. By the time the oil gets to the phasers there isn't much left to keep them happy. That's my theory anyway.
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