1996 Dodge Ram 5.9L ECM Issue

Eagleye134 · Dec 2, 2014

This all started with fuel pump going out ( had like 10 psi at rail ) so I replaed it. Truck still didnt run. Check fuel/spark/air and everything worked. So I came down with it was the ECM. I orignally thought it was the CKPS but after looking into it, if the CKPS wasnt working , I wouldnt have spark. Would there be a dirty/bad air sensor that wouldnt throw a code and cause this? before I go into the ECM.

Merc225hp · Dec 2, 2014

My op is its not the pcm's.

1 Replace the CKPS with a Mopar part.
2 Verify that you have 49 psi at the rail.

Eagleye134 · Dec 2, 2014

I checked fuel at the rail already, even manually fired each injector and saw each of them drop from 45 psi to 20 psi and light diode tested each connector. Is there a certain procedure to put a CKPs in? I read something that these on this truck are calibrated?

rowdyram · Dec 2, 2014

Merc225hp said:
My op is its not the pcm's.

1 Replace the CKPS with a Mopar part.
2 Verify that you have 49 psi at the rail.

I second this.

I was under the impression this was due to a erroneous code not a starting problem.

Eagleye134 · Dec 2, 2014

Are you sure a CKPS wouldnt throw a code if its bad? doesnt it provide the signal for when the ECM should fire the spark (thats why I said the CKPS is good cause I still have spark) I dont wanna buy another part I dont need and ill call a dealer tomorrow and see if my numbers are correct.

rowdyram · Dec 2, 2014

The crank sensor is what's known as a hall effect sensor. It has 3 wires. 5v ground and signal to PCM. As the flexplate rotates the square holes cut out around the edges move past the sensor the magnetic field fluctuates as the holes pass from magnetic induction. This creates a square wave signal to the pcm. There is no surefire way to diagnose it without a lab scope but what you can do is use a DVOM and measure the resistance of the sensor. 5v to ground is ~ 9 ohms signal wire should have a similar value iirc.
And yes it can be and usually does fail w/o setting a code.
If it doesnt work the PCM doesn't know the engine is turning and if it doesn't know that then it can't know its not working.... I hope that made sense

rowdyram · Dec 3, 2014

And yes if it where completely bad you wouldn't have spark...but if it has a "dirty" signal it will cause weak, inconsistent or erratic spark. All of which look good on a spark tester but may not start. I have seen many Chrysler crank sensors do this.
The thing I find odd is you say it starts with the 97 PCM and just runs bad? If so that may rule out the ckps. On the other hand if you have fuel and spark the only 2 options left are compression and the timing of ignition or fuel delivery. Have you by chance checked compression? Does it have a normal cranking rythum?

Merc225hp · Dec 3, 2014

The 97 pcm might be more tolerant than the 96 pcm is to a iffy CKPS, this is why it tries to run.

As you can see the two years use two different CKPS.

97 ckps 56027870-56027870AB
This product fits 739 vehicle variants.
CHRYSLER: 1 models, 9 variants for 2002.
DODGE: 8 models, 725 variants between 1997 and 2008.
JEEP: 1 models, 5 variants between 1997 and 1998.

96 ckps 56027272
This product fits 115 vehicle variants.
DODGE: 3 models, 112 variants between 1994 and 1996.
JEEP: 1 models, 3 variants between 1994 and 1996

Eagleye134 · Dec 3, 2014

Yes I know what a hall effect sensor is and how they function and it did all make sense till I ran the truck for an hr or so tonight (with the 97 ECM at idle) and it turned up these CEL flash codes only:

#12 - Battery Disconnect ( I know this one was suppose to)

#42 - Auto shutdown relay circuit: Open or short in the ASD relay wiring or connectors. (which confuses me since its running and I just replaced the relay)

#11 - No Crank reference signal at PCM: No Distributor reference signal detected during engine cranking. Check the circuit between the distributor and PCM. (This is new)

would number #11 be the main issue that the 97 ECM is more tolerant of? is that the CPS?

rowdyram · Dec 3, 2014

Yes. But since it runs its either intermittent or related to the incorrect PCM and since the ckps cps aren't likely to both fail my money is on the incorrect PCM. Like merc said different p/n so the 97 PCM is seeing a signal value it doesn't like but still able to run.

Eagleye134 · Dec 5, 2014

if its not the crank sensor.. and theres a #11 distrubutor problem... doesnt the distributor control when the pcm fires the injectors and you said I may have a fuel delivery problem (which I no I have constant fuel to the rails) would that be a bad Cam position sensor? it does run with the 97 ECM till about 3000 rpm before miss firing pm every start and 2/3 cranks has a bad start up with that ECM

Merc225hp · Dec 5, 2014

IDK what to say anymore, you keep using that 97 pcm in a 96 truck. Time to buy a couple of parts and go from there.

Good luck.

1996 Dodge Ram 5.9L ECM Issue

Eagleye134

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