2005 Ford F-150
5.4L 3V

Unresolved cam position sensor problem=

Codes:

P0344: Camshaft Position Sensor A Circuit Intermittent (Bank 1 or single sensor)

Freeze Frame: Engine RPM: 600 (code will set at any RPM example: 2000)
Veh Speed: 0
Spark advance: 12 (I’ve also seen it set the code at -3)
IAT: 68F
MAF: 0.7(lb/min)
Fuel sys 1: CL
Fuel sys 2: CL-fault
Calc load: 24.31
Engine temp: 174F
P0340: Camshaft Position Sensor A Circuit (Bank 1 or single sensor)

Background Information:

Vehicle came in with misfire codes and the above mentioned codes. Sparkplugs looked pretty bad. Replaced with new plugs. Ohmed primary and secondary coils of each coil pack, all were within specification.

Vehicle ran better. No misfire codes but will still run rough. When it is running rough it is pretty harmonic and seems like a dead miss.

There are two camshaft position sensors on this variable cam timing motor. These sensors are 2-wire variable reluctance sensors (VRS). The sensors detect the 5 fingers on the phase shown below (marked with red dots). The respective waveform for each bank is also shown below.









The spikes appear in groups of three and then two that are spaced out. Sensor positive goes directly to the PCM. Sensor negative is shared the O2 sensors, fuel rail temperature pressure sensor, power steering pressure sensor, engine oil temperature sensor, cylinder head temperature sensor, and intake air temperature sensor (incorporates in the MAF). This sensor negative enters the PCM as the “Signal return”. From my testing this signal return is battery negative when the key is on. Therefore, these VRS show a waveform only on the (+) wire and the (-) is equal to battery negative), meaning they do not have a floating ground or a bias voltage.

Since the VRS outputs an analog signal the PCM needs to convert it into a digital signal for interpretation. This is done through an analog to digital converter. From what I have read a spike of 0.5V should trigger a “high” or “1” on the digital side.

The PCM uses this data to identify when piston #1 is on its compression stroke. In coil on plug applications, the CMP signal is used to select the proper ignition coil to fire. The second CMP may only be used for the VCT system, however I am unsure.

The crank positon sensor is labeled a “magnetic transducer’ by ford. It has a negative and positive wire with shields going directly to the PCM.

Tests Performed:

Test 1

Hooked scope up to PCM connector using back probes. Plotted both CMP signals at idle and 2500RPM.





Red: Bank 1
Blue: bank 2
Idle
0.4V/dev



Red: Bank 1
Blue: bank 2
2500RPM
0.4V/dev

This test shows that that both CMPs are making a good looking signal up to the PCM. These plots also allowed me to check timing of the camshafts relative to each other. From pictures found online showing 5.4L with front covers removed, the camshafts seem to be in the correct positions with each other.

One thing that I did question is the trace from bank 1 being consistently weaker than bank 2. Bank 1 is the bank that is throwing the DTCs. However the PCM should still recognize them. To test this I pulled the bank 2 CMP sensor partially out to create a large gap. When running the truck, no codes appeared for the second bank, only the same ones for the first bank. Therefore the AD converter in the PCM was still able to detect a “high” on bank 2. Another test to confirm that the amplitude of the trace was not setting the codes was to erase the codes and keep the truck at 2000 RPM until the codes appeared again, which they did. Also, I believe this eliminates the gap on bank 1 from being the problem.

Test 2
Removed bank 1 CMPS but left the connector plugged in and started truck. Runs exactly the same with the same codes. Removed bank 2 sensor in the same manner. Runs the same but triggered an additional code relating to the circuit for the CMPS on bank 2.

Test 3
I’ve read about the starting system interfering with cam and crank position sensors. Therefore, I’ve cleared the codes after start up and the codes have returned.

Test 4
Disconnected alternator in case it was producing too much AC voltage. No luck.

Test 5
Back probed signal return from PCM harness. 0V when key is off, -12V when key is on, -13V when truck is running. This shows that it is not a 5V or 12V reference but just connected to battery ground through the PCM when the key is in the on position.

Test 6
Cam Crank relation



Blue: Crank
Red: Bank 1 CMP
?/div

From some picture of a waveform that I found online the timing seems to be correct. I’m surprised that this waveform graphed correctly because the scope I am using shares the ground for all channels. Therefore I was grounding out the crank sensor (-) wire which is should not be an actual ground. I did end up stalling the truck when trying to re-do this waveform, which made me realize that that the scope has a common ground.

The crank sensor detects 35 teeth spaced 10 degrees apart with one missing. This was confirmed in the waveform




Revving the motor shows the above crank position waveform. This was a long sample that I took. The single does seem to fall out in three places but I think this might be due to sampling frequency on the scope since the codes will set at idle which is seen on the left side of the diagram.

Test 7
Check for mechanical damage to phaser. Bank 1’s phaser does have a slight knock. Rotated crank to expose one of the five fingers on the phaser. No give when pushing on it.

Test 8
Checked for shorts and opens all of the CMPS or crank positon sensor wires. Signal return is slightly grounded through the IAT sensor with the key off but another ford without any problems shows the same thing.

Actions taken:
Replaced the good VR sensors with new ones.

Wiring Diagrams:

 

Thanks for a very informative post. I have noted on the wiring diagrams that the CPS shares a common ground with lots of other sensors and wondered about the prudence of that for a VRS technology sensor. But - such as it is. Thanks again for all your effort.

 

Very good stuff, as far as it goes.

So, what was the actual resolution? Your post includes the following:
Which doesn't make any sense if that was presented as the resolution. Why would replacing good sensors with new ones be expected to repair the problem? If they were good, they were not the problem, eh?

Do you have scope traces of the CMP signals of a properly operating engine for comparison?