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I had an 09 Dodge Ram 5.7l come into my shop on Friday (yesterday). New customer so I don’t know the truck, he said it was running rough, his friend scanned it for him saw it was miss firing out of cylinder 4 and 6, so they put new plugs and coils in it and it’s still missing from the same 2 cylinders. At that point his friend told him he needed a new engine and that’s when he decided to call around to see if this is accurate. I had a little time to cook with it and this is what I found. He does have a miss in both 4 and 6. I did a power balance test and found that neither coil was firing. I looked at the wiring diagram and this is how I interpreted it and this is also where I’m having trouble. The way I understand this diagram is all coils are getting power (battery voltage) with koeo or koer though the ignition/asd relay and they are computer controlled on the ground side? I checked the coils koeo and they all have battery voltage, I started the vehicle and checked working cylinders and you can clearly see the firing event on all cylinders except 4 and 6. Here is another head scratcher for me… Upon starting the car 4 and 6 both have spark in the coils for a good 10-15 seconds then it just quits. So my conclusion is the coils have voltage when they’re supposed to, they just don’t have control from the computer and I can’t figure out why they would have it to start with but then it just goes away? Any help would be appreciated thanks.
You're witnessing the PCM's failure strategy when it sees a dead misfire. Very common on Dodge/RAM products, especially 5.7s. If the PCM sees too many dead misfires on a given cylinder, it'll take spark AND fuel away from the same cylinder for the rest of the ignition cycle.
Unfortunately, that means the loss of spark is a symptom, and not the problem. Have you done a relative compression test? Or, at least listened to the engine during a clear flood crank? If you hear two flat spots in the cranking cadence, there's a mechanical problem.
That makes sense and I wasn’t aware of that, thanks so much and no I haven’t done any other tests other than checking over the work that was previously done to it, making sure parts are right as well as installation and functionality. That’s when I noticed the two coils were firing initially but then lost their spark. You’ve given me good direction, now I know where to go with this on Monday, thanks so much, I will let you know what I find!!
Didn’t get to it on Monday, we were super busy but I had time yesterday and sure enough during a clear flood crank the engine cadence was not good at all. After that I did a relative compression test and saw the two dead cylinders. Waiting on an ok to do more tests and ultimately pull the valve cover for a final diagnosis. Kinda embarrassed I didn’t do this to start lol. I think it was the tune up that was done before it got to me is what threw me off. I decided to go over their work and in doing so noticed the spark issue which took me away from the basics. I wasn’t aware of dodge shutting cylinders down if so many miss fires were detected, this threw me off as well. Perfect example of why basics are so important, thanks again for your help and getting me back on track.
Thanks for the update! Would love to hear what you find if the customer decides to go further.
Don't sweat the spark intentional shutdown thing. You wouldn't be the first tech caught out by that particular pitfall. It's not unreasonable to recheck the work of other shops, either.
Got an ok to move forward with the diag, so I removed the valve cover and right away issue number 1, the oil was the consistency of pudding, turned the engine over and there was absolutely no valve movement in either cylinder. At this point I decided to drain the oil into a clean pan and when I removed the drain plug the oil fell out in chunks… best way to describe it, chunky salsa and pudding mixed together, I had the drain plug removed for a good thirty min and stuff was still falling out.... I think at this point replacing the cam won’t be enough. I’m gonna say his best option is an engine swap. I’ve never seen oil like this lol anyone else ever run into this?
Definitely time for a reman long block or used engine. Oh well. You didn't break it, build it or buy it!
What caused the oil to sludge up like that? Lack of oil changes, sounds like. Let your customer know that regular oil changes will be required if they're gonna make it out of your warranty period.
never be embarased about finding a conclusive result in a diagnostic test, no mater how long it takes to get to it Sleeper......It takes guts to admit you missed something, but really that's part of diag, Doctors miss stuff every day and nobody ever bats an eye.....IMO
Topic Author
Very common on Dodge/RAM products, especially 5.7s. If the PCM sees too many dead misfires on a given cylinder, it'll take spark AND fuel away from the same cylinder for the rest of the ignition cycle.
Have you done a relative compression test? Or, at least listened to the engine during a clear flood crank? If you hear two flat spots in the cranking cadence, there's a mechanical problem. 
