Engine vibrations?

[mahcire]

So, over this summer I made a trip to eastern canada from Ky and have now returned to Maine. During my travels, I get a pretty angry sounding vibration between 65 an 70 mph (110-120 kmph) when I left off the accelerator slightly. Say, when I crest a hill or am decending through the mountains and feather the pedal to maintain my speed. I don't like pushing it over 70 just because at that speed it's already sitting at 2k rpm (so the stock tach says). I have to either left off the pedal more and loose speed or give it a touch more and then end up accelerating. Best I could think up is that it's something in the IP? Maybe she's getting tired and worn out? Any info is helpful.
Also, I have one of my injector vent caps leaking something fierce as soon as the engine is shut down. As a temp fix I installed an electric standby pump spliced in prior to mech pump and pumps into the schrader valve port, powered off starter solenoid with a toggle switch. Just run it for 30 seconds prior to turning the key on and no problems starting. But...in the long run I was curious if these little vent caps are dealer only items?

 

[whenry912]

Wow, I noticed the same thing in my truck on my last 250 mile trip... I was kind of thinking it was drive train related, maybe a ujoint acting up...

 

[mahcire]

It is something like a ujoint, but the driveshaft ujoints were just replaced. Then again, maybe it is something in the drive line. I'm not sure anymore.

 

[whenry912]

Yeah I was pretty sure it wasn't Pump related since I have a new pump and new injectors. I am thinking it rumbles at that sweet spot where there isn't torque on the driveline either from accelerating or decelerating... can't tear into the truck until I finish moving though, so I hope it holds out for a few more road trips.

 

[Knuckledragger]

Since you are driving a 4x4, I would investigate the "death wobble" possibility. Could be the front diff.

 

[mahcire]

Must be the lack of torque on the drive line. I'm not sure of the mileage on my engine so was curious if it might be the IP. I know it's not the death wobble though. Had that back in '08 and that one lets you know it means business. Scary stuff when going around Ky back road curves.

 

[whenry912]

It is something like a ujoint, but the driveshaft ujoints were just replaced. Then again, maybe it is something in the drive line. I'm not sure anymore.

I am leaning toward it being the center support bearing on the driveshaft, did you replace that recently? Mine is pretty old and has some play in it when I push up on the driveshaft...

 

[rjjp]

The vibration is most likely drive line related or a wheel bearing (long 2 or 3 month search to find that one)...
As for the plastic caps on your injectors, just spend the $30 on an entire return line kit.