Dirty fuel injector ?
 

My truck is a 1996 5.2 with only 47k on the clock . Got a little issue and it bugs me so it's time to pick and poke .

Here's the deal . Truck starts just fine , very quick . However , the engine does seem to be , to put it best , off balance slightly .

At idle , hot or cold , you feel a slight vibration .

Rev in neutral/park , sounds great

Driving it under load it feels like a slight tire outta balance issue (new tires , old tires , same result)

My thoughts are an injector is partially clogged from sitting over the years based on :

I have no CEL or codes on the scan .
Not a cat issue , it's been removed and 02 cheated
Plugs , wires , cap , rotor all new and since water tested . No change
Flex plate was inspected , all bolts confirmed tight , no cracks seen .
Harmonic balancer checked and fine
Motor mounts checked (brake stand test , no movement , appear solid)
Plenum is spotless , no vacuum test as per TSB yet , no oil burning .
Injectors have been ohm tested and confirmed to cycle(screwdriver to ear)

I have a complete fuel rail and injectors from my 98 5.9 Grand Cherokee that was wrecked . So , I'm ready to swap them in and see what happens .

IMO , I think injector issue . Should this not work , I will move to the unlikely scenario of testing for low compression on a cylinder .

Any other suggestions to try before I do this ?

Start the engine, let it warm up. Then, unplug each injector one at a time, and see what kind of RPM you drop you get. The one that shows the smallest change, is likely your culprit. Try swapping that injector out, and see if it makes any difference. If it doesn't, do the compression test.

Also make sure the spark plug wires are routed per TSB.
http://dodgeram.info/tsb/1998/18-48-98/18-48-98-v8.htm

+1 @beeker

Gonna try unplugging one injector at a time , see if anything can be noticed .

Plug wire routing was done as per TSB when I replaced the wires . No change noted after all new ignition parts . Being a V8 jeep guy , I have that TSB posted on my garage wall ;) .

I guess the reason I'm leaning towards an injector is because , it's not always noticeable . Most times , yes , but , occasionally it will shown no sign of this vibration under load . WOT , not noticeable at all . I should note , it's really not overly noticeable driving , but , if I gently brakestand it , you can feel it . Inside the cab sounds almost like a clunk but nothing heard from outside . Maybe bottom end related ?

I'll post back in a few days and let you know how the injector , and possible compression tests turn out .

I'm getting 12.8 mpg as per the last tank but little to no city driving , and no winter warmup needed . It's parked in a heated garage .

I don't think this is great at all .My 8" lifted Grand Cher on 35's is about the same but I expect that . I think this truck should do 16ish at least . Better not being driven hard .

If I can find this little issue , I know it will do a little better .

I'm a little slow getting at things since my accident . It wasn't a pretty scene to say the least . If you want some entertainment value to the thread , I can add pics . 98 5.9 Grand Cherokee doing 70 mph vs 2014 Dodge Crew 4x4 crossing the hwy .

Anyways , I do appreciate the input , thanks guys!

Took the truck for a run to the city yesterday . Heard a little tick when I got home , checked just now , and no tick after 1/2 hour warming up to temp .

Now I'm thinking a weak lifter . Kinda makes sense too as I don't feel a power loss accelerating , just that vibration/sorta miss thing at low RPM .

Thoughts ? After 10 cast iron magnum engines , this is the only one I've had tick on me w/o a bad plenum under WOT .

Wow! You've had a lot of Magnums!

Wish I could provide some helpful insight, but I don't think I can.

Try running some seafoam thru it. (some in the gas, some down the brake booster line.)

Finally got to do some testing

Injectors unplugged and each one made the same significant difference . All good IMO
Comp test was dam near perfect as expected from a low k engine , only a 2 psi difference noted on all .

Throwing caution to the wind , I ran my hands over all the plugs wires while running . Well , that turned into quite the shocker . Although new , those cheap crappy plug wires were bad outta the box . I never buy cheap wires , but , the PO had just put these new on right before I bought it .

I ended up put a new set of 8mm MSD wires , and a new MSD coil just because I run them on all my mopars . Problem solved . Took me 130 miles to get the fuel gauge to drop to even on the full mark which is better than before so hopefully this will get me in the range of 16ish mpg or better . I was barely on the gas to go up hills , before , I'd be dropping a gear .

After that , and being very pleased , I installed new front control arm bushings , new sway bar hardware , 4 new Reflex shocks , 4 new 20's and an alignment . I still need to replace the rear spring/shackle bushings but it drives like new now . (I replaced a few TRE's before this)

I ordered shorty headers . I run them on both my jeeps and they made a very noticeable difference . Following the same pattern I have used , I will increase the y-pipe diameter 1/2" later . Good enough for me ;) . Then , I just order a tuner . There's a guy who does the jeep tuners and it is reportedly better than hemifever . I'm sure he can fix me up . The one he did for my 5.9 jeep was very impressive and I was running the Mopar Performance PCM before that , this was way better !!

Thanks for the help guys .