Scanner won't connect with pcm/ecm
 

Got a '98 Cherokee w/ 4.0l. 190k mi. with no problems until now. Had a no start one morning, replaced the CPS and it fired right up. Now it stumbles occasionally at any rpm like it's spark or fuel related it seems. My scanner
won't connect to PCM, I get nothing. Scanner works fine with other vehicles and I've checked all the fuses and connections. Oh by the way I went cheap and bought a $20 CPS off Ebay, new in package. Any ideas?