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NEW TO LS, MANY YEARS BUILDING SBC ENGINES
2003-5.3 LS Engine rebuilt and running great, revved a few times in garage and started running rough scanner said cam position sensor fault.
Replaced sensor, still runs rough and backfires upon startup. Also replaced crank sensor, no change.
UPON UNPLUGING CAM SENSOR, the engine will start fine and no backfire.
This is crazy.
IS IT POSSIBLE THAT I JUMPED A TOOTH ON TIMING CHAIN???
PLEASE HELP
Have you ruled out a bad connection on the cam sensor perhaps faulty wire?
I checked pin 73 on blue connector at computer and I have nothing
I think there is supposed to be 5volts for signal
could there be an issue with the computer?
all grounds are good?
With key on and with running
most people not familiar with the newer PCM/ECM controlled vehicles are very quick to blame the computer/control module. Check the sensor, the connector and wiring. Today, I fixed a vehicle the owner had the crank sensor replaced for a crank no start and P0335. The issue was a bad pin in the connector.
I have already checked the sensor and related wiring back to the ECM
There is no 5volt reference signal coming out of the ECM on PIN 73 of the BLUE CONNECTOR
could there possibly be a PROBLEM WITH ECM??
No voltage at connector for cam position sensor signal 5v
also pulled pin 73 and checked directly to ecm … no 5v signal voltage
both with key on and engine running
DO I HAVE AN ECM FAILURE???
Last edited by 39dan; Nov 25, 2024 at 11:33 AM.
Reason: Adding info
That's the thing there's no 5v coming from it when it's pulsing, as you mentioned below..
Originally Posted by jetech
You can test the cam sensor, it will generate a sine wave that can be "read" on a dvom that has a frequency setting. Here
Guy needs to put it on an O-Scope instead of TYPING IN CAPS LIKE WE DON'T UNDERSTAND PLAIN ENGLISH, AND GO LEARN HOW THIS **** ACTUALLY WORKS.
PCM BLUE 73 is the Sensor Signal back to the PCM as a Sine Wave as mentioned above. No voltage on it you'll see with a meter.
PCM RED 39 is 5v or 12v out to the Cam Sensor. Put a meter on that and see what it is.
PCM Blue 61 is the ground of that circuit.
Again, verify ALL wiring is good all the way from the Cam Sensor Connector to the PCM. Check Pins, pull on wires a little bit to make sure they arent broken also. It's 3 wires, not hard to check.
Last edited by the_merv; Nov 25, 2024 at 08:50 PM.
Right Merv, I should not have said"5V coming from the sensor" I should have said the sine wave comes from the sensor. The crank and cam sensor send a sine wave to the pcm NOT 5v. The PCM can read the amount of time in between the rise and fall in the signal to determine timing events and tell when there is a miss occurring.
39Dan, you said' "Replaced sensor, still runs rough and backfires upon startup. Also replaced crank sensor, no change. UPON UNPLUGING CAM SENSOR, the engine will start fine and no backfire. So I have to ask. Is the cam position sensor still behind the intake manifold or did you do a conversion that mounts on to the timing cover ? like this
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Cam position sensor issue 
Cam position sensor 
