Is it possible this could be as simple as a bad PCM ground connection? Does the coil circuit ground through the PCM? If so, then a loose ground could manifest itself as if the PCM was not controlling the coil ground circuit, right?

 

Sure could. Worth checking out.

 

Well, I poked around a bit in the engine compartment yesterday but couldn't find any loose ground connections. After debating on what to do, I finally decided that I would get the truck towed to another shop that I trust who also does transmission work, just in case the transmission played a role in my breakdown. This guy has done good work for me in the past and is really good about not charging a bunch of labor if he can't figure out what's going on. I talked to him on the phone about my issues and he seemed to have a really good grasp on what to check. So, hopefully I'll be able to report back soon with some progress.

As much as I wanted to figure this out on my own, I finally decided it it was time to set my ego aside and admit that I was probably getting in over my head. Not to mention that it's been 100 degrees here, I don't have a garage to work in (or much spare time for that matter), and I don't really have help to crank the vehicle while I check for voltage with my multimeter. Plus, the roadside assistance coverage I have included with my car insurance would cover 100% of the cost of the tow to another mechanic, but not to my house....so that was kind of the deal-sealer.

Thanks to all of you guys' input, I can now at least talk intelligently with the mechanic about what might be going on. I'll definitely report back when I have some more information, just in case anyone else experiences these same symptoms.

Stay tuned....

 

Let us know what you find out.

 

Well, not much has changed in the status of my truck - it still won't run - but the mechanic working on it has since changed the camshaft position sensor and swapped in yet another coil, to no avail. He said he had checked for power at the coil, but then realized that it cuts out after 2-3 seconds of cranking, as discussed in this thread. I mentioned to him about checking the coil power with an analog multimeter as HeyYou suggested, and he said he would look into that.

I just want to verify something: the camshaft position sensor controls the injector pulse, and the crankshaft position sensor controls spark, correct?

I guess I should suggest that the mechanic check for power at the injectors. At this point though, I'm pretty convinced this is a wiring/PCM issue. I'm not sure what else it could be, since now the coil, crank sensor, and cam sensors are all new...

It's a good thing I have another truck to use ('08 Ram)....and that it wasn't part of the FCA buyback list

 

If power is disappearing at the coil after a couple seconds, even with the engine cranking, PCM isn't seeing the engine turning. (crank sensor, or circuit) If the engine/trans has been changed at some point, check and see if the wiring harness got pinched between them......

 

Thanks! The engine and transmission are both original and have never been removed, but I'm wondering if there is an issue with the pigtail/connector for the crank sensor wiring. Maybe one of the wires got super hot and melted the insulation, so it's grounding out? Or, could something have happened to the flywheel, such that the crank sensor can no longer pick up the "notches"?

Thanks again for all of your input. I would be totally lost without your help.

 

Anything is possible, and it sure won't hurt to check the wiring..... Visually inspecting it shouldn't be too much of a drag, as it doesn't have far to go to get to the PCM. You can verify you are getting power TO the sensor.... and see if you have any signal coming out. If that all looks right..... see if you are getting return signal at the PCM. It's gotta be losing it somewhere......

Have you replaced the PCM? (too many threads here for me to remember. )

 

I think I am beginning to confuse myself, so no worries - I don't know how in the world you keep up with all of the threads like you do!

I have not replaced the PCM yet....I am leaning towards that as the cause, but I don't know much about the process of doing that. The little bit I have read seemed to indicate that remanufactured PCMs are a bit sketchy as to whether they will work. Do you have to have the seller program in your VIN before sending it to you?

As far as checking for power at the crank sensor, that's a good suggestion. What gets me is that the mechanic working on it now said he watched both the cam and crank sensors on his scanner while cranking the engine and they were both producing a signal. He questioned the ratio of crank sensor "counts" to cam sensor "counts"...he said one was much higher than the other, but I have forgotten how much and which was higher - that is way over my head with regard to how the sensors actually operate - but he also said his scanner said that the signals were in synch. So....I am at a total loss. It seems that if both sensors are sending a signal, then I should be getting spark. Perhaps there is simply a wiring issue that is affecting power to the coil, or maybe the PCM really is bad and is not controlling the coil ground to allow current to flow. I'm really guessing here....

Thanks again for repeatedly replying. Like I said....I really don't know how you can keep up with all of the questions people like me throw at you :-)

 

"Counts" is how many times the signal changes state. Crank sensor will be 4 per revolution, cam sensor will be 1. So, totals should be proportional.

Need to see what the PCM is reporting when the engine runs bad/quits...... See what the numbers look like, and should be able to figger out which sensor is having fits.