Cam Position Sensor (PCM)
 

Hello, I own a 97 Ranger 2.3L truck. I saved the truck from being
scraped by Dealer. I have rebilt the truck to almost new condition. The engine runs fine except that I am getting an error code PO340 that is the cam position sensor. I have checked everything and still I cannot find the problem.
The PCM has been updated and reprogramed. The wiring to the sensor is good. The sensor is located on the oil pump. The engine timing belt marks are also lined up. Sometimes the check engine light will go out for a few days, but in time it comes back on. I was informed by the last owner of the truck the the light has been on since the truck was new. I have a service manual and diagram of the pcm but I do not know how accurate it is. I beleve the is more to this problem then I am seeing. I have checked all the wireing from the sensor to the pcm. I belive that the problem is else ware. Does anyone have any ideas.

Roger

Is yours the 3-wire CMP sensor? If so, you might try grounding the black wire in the connector to a known good ground. That would at least rule out intermittent grounding issues.

Another thing to consider is the crankshaft position sensor. The crank signal (CKP) is used by the PCM to test the validity of the CMP signal. Maybe there's a slight problem with the CKP signal that isn't throwing a code, but it's enough to screw up the PCM's monitoring of the CMP signal.

See, "System Monitoring" in Ford DIS/EDIS "Waste Spark" Ignition Systems

P.S. Welcome to FTE.

Have you replaced the cam position sensor?

Cam Possition Sensor
 

Hi, The sensor is a two wire type. Would the engine still run of the crankshaft
sensor was bad? According to my electrical wireing diagram, the cam possition sensor connects to pins 91 and 85 of the pcm. I have checked the connectors and the wireing of the pcm to see if there was a problem. I will check the Crank Sensor. The problem has to be in this system. This is a four cylinder engine with two coils. The crank sensor is a two wire sensor also. Thanks for the info for the Ford DIS/EDIS "Waste Spark" Ignition Systems. I do not think that my truck has a DIS Module. According tho the DIS/EDIS diagram the cam sensor is connected to pin 2 of the DIS module. My sensor goes pin 85 of the pcm. I do not know what the function of pin 91 is. This must be a return line common to all of the other sensors, or this my be a ground. I am trying to use a chilton manual, but is does not show all the details or functions of the pcm. The problem must be in this system because I can clear the code, but it returns. I will keep looking.
If you have any other ideas please let me know. Half of the fun is trying to find the problems.

Thanks,

Roger

All the systems checking in the world won't help you if you have a bad sensor. Total cost for new crank and cam posision sensors should be less than $50. Start with the simple stuff, it'll save you alot of work.

Cam Possition Sensor
 

Hello, I have now have replaced both Cam and Crank sensors and the PCM. I have also schecked all the wiring. I am still getting the error
code PO340. Sometimes the check engine light will go out for a few days. Then it comes back on. This problem has been with this truck since it was built. The problem has to be related to the PCM because I can clear the code and the light goes out. I have also checked the two coils for any problems. I work in the electronics industry and I am an electronic engineer, so I have knowledge of electronics. I do not have complete diagrams of this system. I am lost in checking anything else. There is only a few parts of this ignition system. What else could be wrong.

Roger

Tough one to solve. Since it seems like you've tried everything else, I'm still hung up on a possible problem with the circuitry itself.

From the relevant '97 Ford Manual wiring diagram, it looks to me like the two-wire CMP sensor is grounded by way of the wiring harness itself (that's usually what the dotted lines mean). I'm not familiar with those types of CMPs, though. What does the CMP harness connector and the wire harness itself look like? Is it some sort of cable with two wires running through the center wrapped in a metal ground shield?

As you can see from the diagram below, the 2-wire CMP ultimately gets grounded by way of a splice (S107) into the main wiring harness that runs to the ground screw (G102) located up on the fire wall, just to the right of the PCM harness connector.

http://rockledge.home.comcast.net/Ra....3LCMPCirc.gif

RogerGym, I priced a crank sensor at a local parts dealer and was quoted $220. That seems very high. Also do the crank and/or cam sensors control fuel injector timing also?

s 107 is the magnetic shielding to block interferrance.circuit 359gy/r is your source
voltage(pin 91).circuit 282 db/o is your signal return.I have seen a damaged wire shield cause all sorts of drivability problems(the aluminum foil around the wires.)
If the shielding is damaged,it could be getting interferrance and causing your code.
The only way I know to repair this is a new harness.If the sensors don't help,you may
have to swap the harness.you may be able to test this by overlaying a twisted wire
pair harness pin into the pcm.

The cam sensor is not used for ignition timing in Fords w/EDIS ignition - the CMP signal is used only for SEFI sequencing.

Hi, The wiring harness has a metal shield around two wires. The shield is grounded up near the fire wall. There is about 8 inches of non-shielded wire near the plug that goes into the sensor. This is how it came from Ford. The sensor wire goes up through a bundle of wires from the harness to the PCM. It is all taped up. As far as I can see the shield is grounded. But I don not know if I am getting interferance on the wire because of the shield. Note this problem has been in this truck since it was built. I could have a wiring problem, although I have check the wiring with a meter and it checks good. But this does not check for noise to the pcm. I will check the shield again and look for bad grounds. Any other ideas please let me know.



Thanks,

Also along the lines of RFI "noise", maybe you can try another ignition interference capacitor (the thingy with an electrical connector attached to the coilpack).

Thanks, I will try this. The thing that is confusing is the error code will sometimes clear. Unless there is a poor connection in the shield from the sensor. I will keep looking.

Roger

Did you find out?
 

Hello Roger Did you end up finding the issue. I am having this same issue after rebuilding my 98 2.3 Ranger.