Okay SO. I've got a 1997 1500 5.9L dodge. Since maybe 2 weeks after I bought it, it's had this kind of shaking when I'm between 45mph and 50 mph. It's not a side to side, more like a chugging, but not quite severe enough to consider it bucking. Picked this truck up 3 hours ago from my mechanic for the ujoints and plenum job. Figured might as well get it done before it causes issues. Except now, There's a very clear loss of power and the engine almost sounds quieter. And the 45-50mph chugging is still there. I've had Spark plug #8 foul before and hd that replaced, there's brand new tires, alignment and tierods have been done recently as well. Any idea on what could cause the loss of power after replacing the plenum?

 

That's a miss. At 45 mph, TCC engages, and you feel it a WHOLE lot more. There might be codes for it..... Since the plenum is done, how are the ignition parts? Crank sensor? Cat been checked? How old are the O2 sensors?

 

would it still be a misfire even if I only not feel it 45-50 and over 65? And over 65 is only occasionally. And honestly the guy I bought it from a month ago didn't maintain it very well and didn't keep service records, ignition parts are okay as far as I know, definitely need to check crank sensor and cat, and honestly no idea about the O2 sensors. Truck isn't throwing any codes but they could probably be replaced. The power loss didn't occur until after the plenum was done.

 

Could try just disconnecting the front O2 sensor, and see if it runs any better.

Given its history, I would also be real tempted to see what the cap and rotor look like.......

 

I'll give those a shot.

 

Do any of the intake bolts go through coolant passages?

 

Yes. 8 of them. (two on each side of the coolant cross-over passages in the intake. Although, I don't think there actually IS a passage on the back.) Little dab of RTV on the threads will prevent them from leaking.

 

Is this an issue on the 3.9 V6?

 

Yep. Not quite as common, but, definitely something you should at least check.

 

Will do. Thanks.