I had the same problem with my '00 Merc mountaineer. P0340 kept coming up, even after replacing the cam sensor, wiring to the PCM, 2dry ign cables, sp plugs, head gaskets, swapped coils, geez... still came up every time I cleared it- it would run for the first trip, with no CEL turned on, then as soon as I started it, CEL is on and it is the P0340, again. Finally, I read on another forum that the problem may be the alternator. I just put a new one in about a month before the problems all started. How to diagnose: Charge up the battery. Clear out the codes. Run it until the P0340 shows. Bring it back home. Clear out the codes. Disconnect the alternator. Yes disconnect the alternator. Isolate the battery terminal at the alternator from any short circuits by wrapping it in elec tape. Take the car on the same trip. If the code does not set on, you found the problem. The voltage regulator is transmitting stray AC voltage that is being picked up by the cam sensor or the PCM and throwing the whole system off. Do the test in daylight with no loads on--no radio, no headlights, no blower. I didn't believe it was possible, but now I am a believer. -Mac
I have been scouring this forum and I still have a few questions. Some of the posts are very helpful but rather old. I have a early (May) 1996 with a 4.0 that I have transplanted a (April) 1995 4.0 into. Now the reason I used a 95 was originally because of the transmission. On thing lead to another and I am using the whole drive train. It is becoming apparent one of the issues I missed was this CPS. Now the 95 engine has a 3 wire CPS but of a different style then the 96. I swapped plugs in hopes that would be enough. WRONG, now I have a CEL code 0340. I know my connections are good and the donor ran really well before the swap. I will be double checking my electrical work. I am thinking it is that the 'puter isn't recognizing the 95 sensor. Am I correct in this? I have seen a post in which the whole shootin match is compared physically (wish I knew how to attach to that thread here) and want to be sure that I will be able to install the 96 CPS and shaft in to the 95. I am really looking for conformation, tips or a definite " no can do" from someone who has done this. Thanks in advance. This Forum has been a truck saver.
