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2013 Chevrolet Suburban
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Is this a bad camshaft sensor?

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Old April 16th, 2018, 11:39 PM
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Default Is this a bad camshaft sensor?

I have a 2004 Suburban 1500 Z71 5.3l flex fuel with 290,000 miles. I'm not sure whether or not the camshaft sensor has ever been changed, but judging by the looks of the valley pan area when I changed the intake gasket, I'll assume it's original.
My issue is a rough idle and hesitation upon acceleration. The engine runs perfectly cold, but after a minute or so of running it starts to misfire. I do not, however, have any misfire codes. I haven't since I fixed the intake gasket leak. I also do not have any other codes. Long term trim on both banks is at 22% and short term is staying around 0%.

Things I have already changed that I thought might fix the rough idle (some helped, but not entirely):
Both upstream O2 sensors
Plugs and wires
Fuel pump and filter (fuel pressure within spec)
Intake gasket
Knock sensors and harness
Cleaned PCV valve
Checked multiple times for vacuum leaks with propane and carb cleaner
MAF Sensor
Cleaned and tested injectors (checked resistance)
Throttle body assembly (electronic, drive-by-wire)
Tested coil pack resistance
Installed ram air intake (MAF readings stayed the same as stock, so this did NOT cause my problem)


I have validated that my new MAF works using an oscilloscope, but I finally decided to pull the PCM tonight to access the camshaft and crankshaft sensor wires to needle probe them. First I tried the crank sensor and got perfect square waves starting at 0v and going to 5v and back to 0v. The frequency was not consistent, but it was probably the lack of a stable idle. Then I tested the camshaft sensor and got square waves that looked ok between engine vibrations and shakes, but as soon as the engine started another misfire episode, I saw the following on my oscilloscope.

These all look different because I changed the timing view for different perspectives.





To me, it looks like I have a noisy ground connection, so I'll probably go ahead and change the sensor and harness. It's only $75 or so for ACDelco brand. Anyone think I'm right or wrong? I'm still not too familiar with oscilloscope diagnostic tests. What stands out at me is the fact that the sensor is located in a known trouble spot on this vehicle where the water pours down off the windshield and the fact that these sensors tend to act up more when they're warm or hot.

Last edited by Nicholas McKay; April 16th, 2018 at 11:42 PM.
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