cherokee 89 code readings

hello, will someone tell me wich type of scanner do i need to read the codes?, my cherokke has a 6 in line motor, i saw on the manual how to read v6 codes and '91 and later models, also i saw on another tread that the on off on off on trick doesnt work here, i ask te local stores and they want to sell me a very expensive odb-ii system but they cant assure that it will works

your jeep doesnt store codes.the way that I know how to check them requires an older drb 2 and you have to run some tests with it .at the end of the test it will give you faults if there are any.if you dont mind my asking,what are you trying to fix?

two weeks ago one afternoon it wont start, after a few hours i only found corrosion on the distributor cap, and i replaced it, then it start again, but i thing that it loose power and start vibrating at idle speed. i take it to a shop for a computer diagnosis and they cant find anything, even they told me that the gas pressure are ok.
thanks a lot for your help