2003 Dodge Ram 2500 van - 5.2 L - After codes started - new distributor, pickup plate. cap and rotor, timing chain and gears - wires and plugs less than 5000 miles, new crank position sensor. Cleared codes reset CEL - codes come back on start up and acceleration and CEL is lit again. Missing on idle, smooth on acceleration starts missing again when desired speed is attained and only slight acceleration given. Starts all the time but sometimes starts and dies right away 3 or 4 times in a row. On stopping sometimes idle is high - tap accelerator and returns to normal idle. Any help appreciated!!

 

what brand crank sensor did you use??

 

Purchased from Dodge dealer parts dept

 

well for some reason you cam and crank sensor is having trouble comunicating, have you checked the wiring, should have a 5v reference signal to both, also did you compare the length of the new CPS with the old CPS, theres a small tolerance to the flywheel to make it work,also theres windows on that flywheel to trigger the magnet, did you do anything to the flywheel?? like use a screwdriver up in there to ratate the engine over or anything??

 

I have not done anything to the flywheel or near it. I have checked the wiring visually but not tested voltage. Since the rotor button shaft is turned by the shaft and gear that drives the oil pump could wear there or a worn oil pump cause the problem?

 

This below was interesting when I went to research the issue.

Maybe the distributor is off a tooth or something like that?

The P1391 code can be set for a number of reasons, unfortunately. You've already replaced the two sensors, so they shouldn't be a problem at this point. I'll shoot you a short list of things I'd check, let me know if any stick...

Harness problems. You've wiggled wires, but I'd suggest looking at the harness in the immediate area where they plug into the top-left area of the engine. Upturned valve cover edges, protruding bolt heads and just plain metal everywhere may have worn some insulation off in a particular place. Inspect the harness carefully anywhere it will normally come into contact with metal... whether it's sharp edged or not.

Cam/ crank sync. The cam sensor needs to be within 10 degrees of crank to by in-sync, otherwise the cam signal isn't recognized by the PCM. The fleeting nature of a cam sensor sitting right on the fence between in and out of sync would be tough for the PCM to figure out, so it sets a blanket code (P1391). If you have the capacity to set distributor index with a scan tool, that would be the preferred way... set it to zero degrees of offset. If you don't have that luxury, I can describe how to do it manually, which will get you easily within the operating window.

Damage to crank sensor tone wheel. If the transmission has been removed, the tone wheel on the flexplate (auto) may be bruised a bit. It doesn't take much to mess up a square wave signal, which is what the P1391 will be telling you. Anything that could cause intermittent loss of signal or an "unclean" square wave could easily cause this code to set. Measuring the tone wheel with a dial indicator as the engine is slowly rotated would tell you if there's a concentricity issue... if you could GET a dial indicator in there, that is.

Loss or partial loss of the 5v power feed to the main sensors. Unlikely, since so many sensors use this circuit and none have issues bad enough to set a code, but I can't exclude the possibility completely. You might hook up a voltmeter to the 5v feed to the orange wire on any of the major sensors underhood and to the violet/ white wire to the trans governor pressure sensor (Pin 31 of the PCM C2 connector). Intermittent short to ground will cause some strange things to happen on either of these 5v feed circuits.

Sensor ground. Just as important as any other circuit, sensor ground must be in good shape to make everybody happy. This is the black/ light blue wire you'll find throughout the underhood area, routed to all sensors.

Oddball harness shorts caused by a bad component. I had a downstream oxygen sensor short internally once upon a time, sending ASD voltage back on the signal circuit to the PCM. It overloaded the internal board shared for voltage sense between a few other sensors and caused some odd overvolt problems, even though the other circuits weren't directly affected.

I'll stop there for now, I figure you're probably waiting. See what you think and let me know what you find. One thing I have to caution you about... aftermarket cam and crank sensors can be worse than the original BAD units. Be careful about putting too much trust in non-Mopar cam and crank sensors (in anything).

 

Replaced throttle position sensor and idle control valve - cleared codes and CEL.
Test drove - no codes and CEL did not turn on. Still have miss or backfire at cruising speed when accelerating slightly. checked for visible wire damage or loose connection - none found