Ok guys, I need some help. I'm an experienced amateur, being the daughter of a mechanic and having worked on my own and friends/family's vehicles for almost 30 years - but this darn Dodge has me befuddled.

Awhile back I had some problems with a crank/no start which ended up being the camshaft position sensor aka distributor pickup coil on my 01' Ram 1500, 6cyl, 3.9L engine.
At the time, I'd been through every possible repair, replaced both cam and crank sensors, all plugs, wires, cap & rotor, and finally resolved the problem.
Here it is about 18 months later, and I started having some surging and jerking, stalling and misfiring, mainly after the engine warmed up. I had p1391 code, so I could often let the truck cool down, clear the codes,
and drive to wherever I needed to go around town. (I'm in a small town, so leaving town to go elsewhere means 15 minute 18-20 mile highway trip I don't risk)

Ultimately this time around, I replaced the cam sensor, and drove it fine for half a day, including out of town, and it seemed better than it had ever been. Later that night I tried to go down the block and it started
it's surging and jerking and stalling and super long crank times again, but I got it back home. Then I replaced the crank sensor. Small temp improvements, but back to the same, and had to be towed home.
(I should specify that I've used O'Reilly parts, with lifetime warranties - so I didn't have to pay to replace them this time around - they were already under warranty, and O'Reilly is all we have here in town, so that's why I use their parts I know, not the best choice but...)

So I have a cheapy Innova code reader and a digital multimeter for diagnostics - so I got the dmm out and checked, and the output voltage from the sensor with the engine running varies between 1.75 and 3.45, never gets near the 5V....BUT I backprobed the harness connector and found what do you know, but I have no continuity between the ground wire and supply 5v wire. With what little I know about electronics and voltages, etc. it seems like the signal from the PCM to the sensor isn't coming in as the full 5V reference it should, so that would affect the output range? Am I right? Or does the sensor not care much about the input reference voltage signal?
Where do I go from here? Can the plastic connector (and inside) being dirty cause this? Would it be worthwhile to try cleaning it? Can I just replace the plastic connector, or is there more testing of the rest of the wiring between it and the PCM that must be done? The wiring *appears* in decent shape, with no obvious splits or breaks in wiring, melted insulations, etc.


*Also, at a later date, I have a code for a Governor's Pressure Sensor that I need to take care of, but right now my concern is getting the truck running and driving.
I'm thankful for any help you can give! Thanks in advance

 

The reference voltage definitely needs to be a stable 5V. The reference voltage is shared by cam position sensor, crank position sensor, throttle position sensor and the manifold absolute pressure sensor. Any of these could be the culprit of making the supply voltage wonky. As for measurements at the cam sensor, AFAIK it's a hall effect type which is semiconductor so you won't be able to measure continuity from supply to ground. The output signal changes fairly quickly, if you have a 600 rpm idle the camshaft turns 300 times in a minute or 5 times a second. The DMM is not going to be fast enough to register that correctly. Ideally you'd have a scope for that but you could try to watch the DMM during cranking (disable coil or similar) which turns the engine quite slowly.

 

Thank you for your reply! How can I double check the reference voltage? When using the dmm, backprobing black to ground wire, red to supply wire, engine off, it shows the 5V. I didn't check it while cranking.
I checked for continuity between the supply and the ground and found none. Checked for continuity between ground and output and it was fine.
I was really a bit cautious about using the dmm to test, because I've heard some places say that you must disconnect the PCM before testing, but that didn't make any sense to me. How can I test the supply from
or signal to the PCM with it disconnected?
I know the dmm doesn't update as quickly as the voltage changes, but I thought it would at least show me if it was reaching that 5V at any time, which it isnt. Given the resources I have at hand, what would you
recommend I try or test next?
(Again, appreciate any help!)

 

You could check the 5V sensor reference during cranking but I don't think this will give any better insight. What makes it a little more difficult is that both the crank and the cam position sensor have been changed with aftermarket parts, and according to anecdotal evidence on this and other forums aftermarket parts don't work as good as the OEM sensors. As described above, the cam sensor is fairly easy to check with a voltmeter. Disconnect the coil, crank it with the starter or even by hand and there should be a visible switch from close to 5V to 0V and back. I don't think this will work with the crank position sensor because the notches are pretty small.

As for testing with a DMM, as long as you are in DC voltage range that does not cause any issues. In current mode it could short out something, and in resistance settings it does apply some (low) voltage.

With P0340 being cam position sensor circuit malfunction, and P1391 is CMP or CKP intermittent I'd dig into the cam sensor as described above, followed by checking the wiring closely. Pay attention the connectors at the ECM too.

 

Thank you so much! I'll do that- check output during cranking with coil disabled. After my checks the other day, I noticed that the truck ran idling until warm, and when I tried to drive it a few minutes later, engine still warm, the symptoms all reappeared - However, this time, the p0340 code was not set, only the p0748...I know that I need a transmission fluid and filter change, so I suspect that is why, but any idea why it wouldn't register the 340 code again?