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Discussion Starter #1
Originally got p1391 and p0340 changed the crank and cam sensor. then cleaned the IAC. sprayed connection cleaner. Truck is running better only bounces around by 100 rpm now but is still throwing the p1391 code. Any suggestions where look next?
 

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P1391 is intermittent loss of crankshaft or camshaft sensor signal. The fact that your tach is bouncing around kind of backs that up. I would do a careful inspection of all the wiring from those two sensors to the PCM. Start by looking where the cable bundles come close to the engine or any other metal object to see if there is any place that the insulation is worn or frayed. Also look for signs of critters gnawing on wiring, etc.
 

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Glad you got it figured out. The downstream O2 sensor runs to the same wire bundle as the crankshaft position sensor, doesn't it? Possibly some interference from the O2 sensor wiring?
 

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Discussion Starter #5
I am unaware of where it runs, tomorrow will be the replacement of that o2 sensor as well as the front. Pretty sure it’s been 20 years since they’ve been touched even. Then we will see if I start getting some codes and rough runnings again.
 

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These sensors are known for stripping the threads out and just spinning around in the pipe bung. Here is a tip. Get a thin wrench like used in many motorcycle tool kits. Find one that will just fit between the bung and back side of the sensor nut. Flatten to a point the edges of the wrench where it can be drove between the bung and sensor and then slowly turn the sensor out while periodically tapping the wrench farther inward. This creates a wedge forcing the sensor outward while turning it.
Hopefully you will not experience this problem but if you do be prepared.
I also tap the bung out to freshen up the threads. A spark plug hole reamer works great.
Good luck
 
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