So the plenum rebuild kit complete. Still having a rough idle and a shake at 45 in low rpms. I have changed the tps, aic, cps, cleaned the throttle body, changed spark plugs, wires, rotor and cap, injector o- rings and possibly my mind on owning another dodge. Any other sensors it could be?

 

Throwing out a random possibility here. not very tech savvy with these trucks but check your coolant temp sensor. i read they are also a fuel choke if they go bad, ive had a few trucks with one go bad and was almost identical to your problem, but didnt have the engine shake at 45.

 

I changed that also along with putting in a new thermostat

 

How bad is the shake? Does it go away, or greatly reduce when you turn off O/D? Did you replace the plug wires? (if not, get a nice spray bottle, and mist them with water, engine running. If you get a light show, replace them.) Did you route your wires per the TSB? (it's in the faq section)

 

Yes the wire have been replaced. The only time it shakes is when I get to 45 and it shifts down to over drive then give it just a little gas it doesn't do it at 40 and it doesn't do it at 50. It doesn't feel like the shake is coming from the transmission.

 

Was this done? If not I would do one asap.

 

Just did a compression test. All cylinders are 140 to 150 psi except 3 with was a dissapointing 60. Put a little oil in the cylinder and retested. It was still reading 60. I'm thinking its a burnt valve.

 

might also be cracked heads. its a common problem on these engines.

is this a new problem, or has it always done it?
and how miles on the engine?

your gas mileage probably really sucks too, since your mostly running on 5 cylinders while feeding gas into all 8.

no easy, magical fix...
only a few choices that i can think of -
sell it or better - trade it in.
live with it, and turn OD off to keep the rpm up.
pull the heads and take them to a machine shop to be checked, and if good - rebuilt. cost? plus gaskets.
replace the heads with new ones from clearwater or other for about $600, plus gaskets. (and hope the rings are still good)
replace the whole engine with one from the junkyard, with minimum new parts cost. once you start adding new parts, its hard to stop and pretty soon you've spent a bundle. (seals, gaskets, timing chain, oil pump, water pump...) do move over your new parts.

 

Yes it recently started doing this. If the head was cracked wouldn't there be antifreeze in the oil? When I just replaced the plenum I didn't find that. Right now my gas mileage is average 12.5. And none of my cylinders are fouling plugs

 

Could do a leakdown test to verify where compression is going....

Heads crack around the valve seats, you won't always get coolant into the combustion chamber. Just a severe loss of compression. Also gives the valve a chance to burn nicely. This may have been an ongoing problem that just wasn't quite so noticeable......

In any event, 60PSI on one cylinder fails in two ways, it is certainly below 100PSI, and it is significantly more than 25% below any of the others.... dh pretty much outlined your options..... time to figure out what ya wanna do.