Trouble with a 2001 Dodge Durango misfire... 4.7L v8
Hey all. Just joined this forum because my parents have a 2001 Dodge Durango with the 4.7L Magnum V8 that has been giving us hell the past couple of months, and I have run out of ideas and they are ready to give it to a shop to tear apart and I would like to save them money if at all possible.
What It's Doing:
About 2 months ago, my step-mom came home from wrok complaining that the the car was overheating and she was scared to drive it in town anymore. Upon further inspection we noticed that there was a ton of coolant leaking, so my dad, being the "master mechanic" he is, runs out and buys a new thermostat and has me install it for him. Drive it around, bring it back, still leaking. He goes to fill up the radiator and I watch as he pours it in the top and it runs right out the bottom. Futher inspection finds that the radiator has rotted through. $160 and a new radiator later, car doesn't leak anymore, but since doing that we have noticed the car making a loud tapping noise between 2k and 3500 rpms when under a load. If you are in park and rev, you don't hear the tap.
I used to own a Ford Probe, and it had developed a stuck lifter from when my parents were driving it and ran it out of oil (had a leak they claim they didn't know about), and the lifter tapped thereafter. Didn't think anything about it, but then a few days later we changed the gas cap from a pre-existing CEL and when dad cleared the codes we found that the car also popped a CEL for P0306, a misfire in Cylinder 6, and a few different CELs for the EVAP system. So I traced the vac hoses and found about 6 hoses that were either cracked or completely split, and got rid of the EVAP Codes. However, this misfire will not go away. It can only be heard from 2k to 3500 rpm when accelerating (let off the gas at 3000 rpm and you can't hear it anymore). Also, I noticed when test driving it again tonight that if you are in a low RPM, it is very sluggish when you accelerate and it goes to downshift. Once it downshifts it's fine, but right before it wants to bog slightly. Aside from the bogging before downshift, the car has no performance weakness.
What we've done:
Replaced All Vac Hoses (due to EVAP Leak)
Spark Plugs (replaced with Champion OEM)
Cleaned Coil Packs and switched pack from #6 to #5, no change
Cleaned Injectors and switch injector from #6 to #3, no change
Checked Fuel Pressure, it's fine
Changed All Fluids
We are really running out of ideas. It's not getting expensive yet, but we are running out of the cheaper fix ideas. Also, when I pulled the #6 spark plug today to check it's condition, it had unscrewed itself someone. When I installed them a month ago, I torqued them all to spec, so I am not sure if it making it's way out is a symptom of the problem or what. Car drove the same after torquing it down again, and the plug looked fine. Had been firing no problems.
Also, the CEL only comes on after about 45 minutes of driving. I drove into town while testing it, got food at Taco Bell, and came back before it finally came on.
Anyone got any ideas? Searching has not turned up anything I haven't tried, except one that was from 2002 wiht a guy talking about Dodge having a recall due to several claims that the Durango heads were cracking between the Intake and Exhaust Valves near Cylinder 6. Really hope that's not it, but if I check this after I replace my Fuel Pump in the Jeep (why does everything have to break at once?), then I guess I'll disconnect the HVAC lines and pull the valve cover to check it out...
All help is GREATLY appreciated... Will offer a 10% discount good off any products on my website to anyone who gives advice that leads to us fixing this without a mechanics bill... (Truck parts available upon request)