I’ll try to keep this as brief as possible, but this has been a problem that has been going on for 2 years that I have been unable to fix and it has limited where I can drive the durango. Luckily, it is a utility-use vehicle and not our daily driver (any longer, but because of this problem). I have never experienced anything like this before and have stayed away (mostly) from throwing parts and really tried to diagnose as much as I can. So here goes.
2006 Durango, 4.7 SLT, ~ 160k.
I won’t get into the life history, but here is what I cannot resolve.
If I am driving around town (less than 45 mph), it drives perfectly fine. No issues at all. If I am driving on flat straight road at 45+, it drives fine, no issues at all (95% of the time). However, say I am driving on a highway that has some flat stretches then some hills. Not super steep, but steep enough to make it drop down a gear if I hold throttle steady and, of course, if I press harder on throttle. I can be cruising along at 45-60mph+ on flat stretch, then go down a hill, but have to go up a hill, same speed, I start losing power, CEL comes on (for multiple misfires, usually bank 1) At the same time, I hear what sounds like afterfire in the cat area or some other area of exhaust on driver side. I can feel it in the floor as well. It’s constant as I am trying to head up the hill pop, pop, poppopopop, pop pop, etc. Once I get to the top of the hill and it levels out, it is still struggling, but usually it clears itself up. I assume there is some recovery time. So long as I am driving flat again, it drives like nothing happened. Again, if I am below highway speeds, I can climb hills no problem at all and this doesn’t happen at all - THIS is what is driving me nuts. It is VERY specific - highway speeds/under load.
Here is what I have checked and what I have replaced:
Fuel pressure is spot on
Cylinder pressure is within specs for dry and wet, with no concerning deviation between neighbors
I replaced ALL plugs (Champion Copper, also tried NGK and a few other brands, but Champion has been best)
Replaced ALL coil over packs
Replaced cylinder 5 and 7 injectors (they seemed to be the cylinders throwing codes the most when specified)
Also replaced cylinder 3 injector as it had a crack on the side that concerned me.
Post Cat O2 sensors have been replaced (due to CELs at various times over the years), though I know this is not really relevant.
I will admit, this thing does have pre-cat O2 sensor problems. I have had to replace bank 2 sensor 1 once before and now need to change it again due to a heating problem. This, however, is the opposite side where I have the problems, it seems.
New Battery (within the past year - had lots of corrosion)
Alternator tests perfectly fine.
Changed air filter and all that good stuff.
Ran Seafoam in crankcase, intake, and gas. It helped it run smoother, but did nothing to fix the problem.
No coolant contamination in the oil at all. Although, I do think I have a leak somewhere as I get white smoke when I first start it that is more than just condensation, but it clears up pretty quickly. I have to put in enough coolant from min to max no more than 1 time a year, so it is slow, whatever it is. No signs of hose leaks or any other leaks underneath.
It starts fine, every time, no matter the temperature. It idles mostly fine. If I concentrate hard enough, I can feel a little teeny bit of shakiness on idle, but not sure if this is normal for this vehicle and age.
From the wires I have inspected, they are all still sealed up, no rotting that I can see, though the one thing I haven’t done is really get in and diagnose electrical, though no other signs of electrical problems.
I just don’t get it. Except for this one very specific problem that happens at a VERY specific point in time and is repeatable every time, it runs great.
I love the truck for a good 4 wheel drive, towing, and the getting-supplies-from-the-lumberyard vehicle, but this problem has limited me in using it.
Thanks in advance!