Its going to be a little long winded, but bear with me. I have a 2004 Rubi with 120k miles on it, auto, stock gears, 35's. I will be regearing to 5.38's after i hear from Mr. Bransford if he still likes his setup. Anyways, heres the back story... I had a sub in the back of the jeep that was powered from an amp under the drivers seat. Everything was working properly and I decided to ditch that setup and just do an all in one powered sub that fit under the drivers seat. Since all the wiring for the amp was already there it was a slam dunk install. I hooked it up and all was well. That is until i came back out to the garage to mess with the sound of it a little. Out of nowhere it starts making a very loud sub harmonic feedback noise. Since I got it from Amazon, it was going back immediately. As i went to unscrew the mounting screws that were mounted into the jeep tub, I watched as they sparked as i unscrewed them. As soon as I got all the screws out and the speaker was no longer in contact with metal, it worked fine. Obviously some kind of internal grounding situation was happening. I pulled the thing out of the jeep and boxed it up to return it. Now for the real issue.
The next day i was leaving first thing in the morning to go wheeling. As i left my driveway I got about 1/4 mile and out of nowhere the jeep starts lurching and sputtering around 2k rpm. My first thought was fuel pump since mine started whining after i put the savvy gas tank skid on. No i didn't replace it when I had the tank down ( rookie move). So i ordered the fuel pump and through it in. Still same issues. The next thought was tps since it was happening around the 2k mark and i know that sensor starts really doing its thing around that rpm. Through that in. No change. However, when doing that test drive its then i noticed that the speedometer was reading about 90 when i was really doing 25. Well that explained the fuel cutting out.
From here is where things get interesting. First thought was speed sensor. Well, the great folks at Chrysler stopped producing that sensor in April of last year. After scouring the internet for the part without any success, I remembered that the jb conversions short sye kit used a sensor that looked an awful lot like the one in my jeep. so i emailed them. To all who may need a tj rubicon speed sensor, the awesome folks at JB will sell you one for $40. Its the exact same part. That wasn't my problem though. Next, I read about the tone ring breaking the key piece and freewheeling in the t-case. So i pulled off the back to inspect and see that everything is as it should be. I needed to change the fluid anyways so not a total waste of time.
My next attack was on the cluster itself. I have an extra one kicking around so i swapped it out to no avail. same issue.
So as im working towards the front of the jeep, i also read where some people have fried diodes in the alternator and thus allowing some low level ac power to feed back through the ground side and mess with the sensors. Que the new alternator and battery. Nope.
As a last ditch effort I put my tail between my legs and took it to the dealership. If Waterdog were still around he would have slapped me
. I told them I wanted them to reflash the computer and see if it would set things straight. They did that and set the computer to now read that I'm running 35's but it didn't fix the speedo issue.
Heres the crazy part... I do have a speedohealer on my jeep. Before all this happened I had it set to a positive 6.6. I now have it set to a negative 65.4 and the speedometer reads to within on mph of gps. How is it possible that the computer is reading consistently wrong? Like it somehow has some arbitrary positive setting stuck in it. The jeep seems to run great with the speedohealer as the band aid fix, just curious as to the real issue. Btw, when the dealer said they thought the problem was in the differential that's when I stepped in to rip it back out of their hands. Sorry for the long explanation, just a really weird set of circumstances. Also, are 5.38's still the way to go on 35's with the auto? Thanks brothers and sisters