I think that the timing is not advancing, it runs but rough with no gitty up, is there some type of a mag. on the flywheel or counter balance that sends a signial for the dist. to catch up.

is spark dead (tested) on all cylinders/?? if not you be barking up the wrong tree. (for sure)
no turbo charged, 3.8L V6 right?

USA car, yes?
the CMP cam sensor kills spark DEAD TOO, so why pick CKP?
then scan the PCM for CKP errors P03xx
same answer all cars USA, 1996 up, OBD2 PCM
here is are the steps.
1: scan tool connected. to cars DLC jack 16pin,
pin 16 must have 12vdc key or the fuse to it is blown!!!
2: key on , see scan tool work now and shows talking ok (communicating)'' can even see stored errors (DTC) last run.

3: crank the engine for 10 seconds, or 10 turns of crank shaft. actual.
4: release the key (not off)let the spring push the key back.
5: do not turn off the key even wait here 1 full minute or more
6: scan PCM AGAIN AND SEE THE p03XX CODES, IF YES BINGO
all usa cars same answer, 1996 up is fed mandated OBD2 .
7: the test beside PCM scans above is using a scope to see the output live.

the CKP is 4 pins HALL sensor know for super good signals all the time. (unlike 2 pin mag type)
related.
DTC P1336 (learning ckp failed)
DTC P0336(ckp errors)
DTC P0336
and more codcs for CAM sensor and if cam drive is loose.

all this and more is in the factory service manual./
now where is it, the CKP hunts endless on endless forums
now I will paste the manuals instruction (removal) verbatim.

1. Disconnect the negative battery cable.
2. Remove the serpentine belt(s) from the crankshaft pulley.
3. Raise the vehicle on a hoist.
4. Remove the right front wheel and tire assembly.
5. Remove the right inner fender access cover.
6. Hold the flywheel with J 37096 Flywheel Holding Tool.
7. Using 28 mm socket, remove the crankshaft harmonic balancer retaining bolt.
8. Remove the crankshaft harmonic balancer using special tool J 38197 Balancer Remover.
9. Remove the crankshaft position sensor shield (do not use a pry bar).
10. Disconnect the sensor electrical connector.
11. Remove 2 attaching bolts from the crankshaft position sensor.
12. Remove the crankshaft position sensor from block face"

end Easter Egg hunt 10000000

I would make sure the new balancer is lined up correctly.. make sure nothing is bent or warped..

You should be able to turn the serpentine belt by using the alternator pulley. That would also turn the crank shaft.

check the timing setting as it may be too far advanced ( set at 5 degrees advanced to start) check and adjust the fuel setting of the main jet as it may be too rich at idle.. You state that the flywheel was out of true and with the vibrations I suspect that the crank shaft may be bent. Something that would not normally be checked

This what I think is happening. Your engine is running rich because the ECM thinks it has too much air and so injects more fuel. When you now introduce air, by taking th e vacuum line off, the fuel mixture is now more balanced. Have you cleaned your MAF sensor? Also make sure your engine coolant is full.

Go up on gas octane to 89.

Hello, You should be able to run a scan and find the problem. A sensor would trigger a "check light" and give a number Code. Autozone, Oreillys, and Advance will scan your vehicle for free.

If you have no check light, then you need to do some old fashion testing without a computer. Use a Vacuum gauge on the running engine and see whether the vacuum levels are steady and if they are at a normal level. Bad valve springs and bad compression will make the needle bounce.

You can do a compression test either by using handgauge or with a computer using a cylinder balance test. The balance test can be performed by a shop having better testing equipment. It will show you how much work each cylinder is doing and will identify each cylinders' characteristics without opening the engine.

You can also check the seams of the Intake manifold with a mist of water from a spray bottle while the engine is running. Any change in RPM will indicate a manifold leak. Once you find the leak, fix it and then try looking for an additional problem if it is still running rough.

The last item I can think of is the timing. Some of the sensors are adjustable and may not be in time.

check plugs, wires and mag pack its what your plug wires go to from spark plugs. Im thinking bad plugs or one wire is bad

I have been dealing with the same issue in my 05 kia optima for over a year with the vibration getting worse as time went on. I found excessive carbon buildup on the counter balancer shaft which put the shaft out of balance. The vibration started out very light in the beginning and continued to get worse as time past to the point that the steering wheel would shake in any gear that the car was in. We found this solution almost by accident by turning the balancer shaft by hand an felt a very slight roughness while turning it. That is when I made the choice to pull the shaft out an we send a very visible problem.

topmarincons: In checking this car for flywheels available, Nissan only lists one part number 12310-2Y910. I could find no other references or part numbers superseding this one.
When you list a single sheave, it sounds more like you are describing a front crank pulley. Again, in researching part numbers, I could only come up with one number :12303-31U10. It is commonly referred to as a "Harmonic balancer". In looking at an exploded parts diagram, it shows a serpentine type pulley."Single sheave". As far as sources: This particular part rarely fails.
New, it, dealer retail price is $234.33
Check with salvage yards, you can buy them for a fraction of that price. Another option is to buy an "UNDER DRIVE" unit. This is a part which will add horse power by cutting down on some of the rotating mass, yet not affect that crankshaft harmonics which would affect it at high RPM's. "UNORTHODOX" racing, on-line I believe is one source. Good luck.......