My pajero jr. automatic trasmision has no power on drive mode.transmission oil already change. what is wrong/

Hi try to clean the converter and change the trasmision oil

Marion, Check links below for proper transmission fluid to use in your application.
Warning on the use of incorrect transmission fluids.
Info. below provided by assassin of The Mitsubishi Pajero Owners Club
Many people are using the incorrect specification in auto transmission systems requiring Dia Queen SP III transmission fluids, this is due to confusion arising from the fact that many people believe DEXRON III is suitable, IT IS NOT SUITABLE FOR MITSUBISHI AUTOMATIC TRANSMISSIONS requiring SP III.

Pajero automatic transmission fluid and filter change

The Mitsubishi Pajero Owners Club View topic Auto Transmission Fluids

Recommended Type of Transmission Oil for Mitsubishi Pajero How Much Do You...

I had a similar issue with my pajero jr, the solution was to replace the transmission ECU.

Often the oil is neglected try a change first, it should be done quite regularly on autos. (and make sure you use a dexron oil http://en.wikipedia.org/wiki/DEXRON)
Gearbox rebuilds are costly, I fear on a 93 it would be dearer than the vehicle, however you might find a good second hand one.

I believe you have run into a classic problem with automatic transmissions, one that is going to be expensive to repair. You noted that the car is a 1992 model so I will make a quick assumption of 10000 miles per year and say that the car has close to 180k miles on it. If the transmission fluid and filter had not been changed on a regular basis or this was the first ever change, then what has happened is that with the fresh fluid you have an issue where the old clutch surfaces can no longer "grip" their attending drive plates. I am also assuming here that you did put the correct type of fluid in the transmission and reinstalled the filter correctly. Automatic transmission fluid has a very high level of detergent, it also bonds with the clutch discs over a period of time and introducing fresh fluid tends to cause problems with loose debris, destroys the previous bond with clutch surfaces which are already worn down and it is certainly more "slippery" than old fluid.

I really hate to say this as I do not believe in the bottle treatments sold for automatic transmission woes, but this is one case where a bottle of the stuff may re-introduce some friction modifiers that you have lost. For the cost of the treatment it is probably worth the attempt. The other options become more expensive. Having the valve body removed, cleaned and reinstalled might clear the situation if there is any minor debris hung up in any of the shift valves. The last solution is a total transmission rebuild with new clutches/plates/seals and gaskets.

Sorry for the bad news, but that is my take on it.

Check the oil level of the gearbox while the car is idling. if the oil level is to low it will give you those symptoms. If the oil level is on its mark it might be that the clutches in the gearbox that is slipping

The first change/flush will usually be at 75,000-100,000 mi.

I have a pajero junior 1997 4A31, I am having problems, with my gear, when take off in D the car is slow, and up hill no power in 2nd & D, in Load ok. Plse advise. Thank you.

Pull the distick and smell the oil. If it's discoloured (black or dark brown) you know the transmission friction plates are burnt and needs a rebuilt.
Cheers