Weird P0340 issue

[rolltide6019]

Guys, new to this site - thank you all in advance.
On my 98 4.0 OHV I've been working on a P0340 (camshaft circuit fault). So here's the deal...this fault existed before I changed the engine. I put another synchronizer and sensor on it AND I can see the pulses on my oscilloscope going into pin 85 on the ECM; a nice square wave of about 13v. I figured it must be the ECM since all the right signals were there so I purchased a new one. There is no difference with the new ECM. So I have a new CPS, new ECM and the wiring checks out between them and I have a signal that matches whats suppose to be there (far as I know). There are no other codes. I've read in some forums that a bad alternator can cause this but I've disconnected mine but it didn't make any difference. After you clear the code, it appears immediately when you crank the engine up. The engine runs pretty smooth overall. So what can be causing this continual P0340? What else haven't I considered or checked? BTW, this is a 3-wire sensor (not 2 wire)

Thanks for the help!

 

[holyford86]

have you verified that the sensor is installed in the correct orientation and all 3 of the wires are sound? it seems as if you've been pretty thorough, but not sure if you've verified these two things the way I've read it. One of them should have 12 volts and the other should be ground

 

[rolltide6019]

Thanks for the input - The sensor will only go on one way; it's keyed to fit on top of the synchronizer so you can't really put it on wrong. Yes, one wire is +12v, one is ground, the other is signal back to the ECM. You can watch the pulses going into the ECM on pin 85, a nice square wave. Seeing that sort of eliminates wiring issues although I ohmed the wires out. I don't have a wiring diagram so that would be helpful if you have access to one.