1990 Cherokee will not upshift (transmission? computer?electrical?)
I drive a 1990 Jeep Cherokee, 4WD, 4.0L, automatic. It only has 80,000 miles on it but it drives weird. I have to get up to 35mph and 4200rpm for the Jeep to "upshift" into the next gear. Then, I have to go almost 65mph and 4200rpm to get the Jeep to upshift again. I have to begin the whole process over again if the Jeep falls below 25mph (after reaching 35mph) and 55mph (after reaching 65mph). As you can imagine, the run-out at 35 mph and 65 mph seems like the engine is going to blow and then it finally kicks in. It makes for a miserable drive and makes driving "work" versus pleasure. I have a lot of traffic in my commute also, which makes it even worse. Also, if I punch the pedal to the floor, there is no "downshift" that kicks the Jeep into a passing gear. It just gradually gets faster with no "passing gear". The Jeep runs at 3000+rpm when I am going 65mph and it should be around 2100 rpm. I had a Mercury Cougar that had the same exact problem and it was the fan clutch (doesn't sound right, but it was). I replaced the fan clutch hoping my problem would go away, but it did not. What is my problem? It sounds like an electrical problem as sometimes it will run like a normal Jeep for a week or two, then go back to the Jeep from Hell again. The Jeep is in great shape, but I need it to perform better....or else. I have changed the TPS, fan clutch, transmission fluid, and transmission filter. Could it be the computer or the transmission computer? I could really use some expert help to diagnose this problem before I take it in to a mechanic's shop to put it under a scope. I'm a do it yourselfer and would like to fix on my own before I give in to the shop.