1998 Jeep Cherokee Tune-Up - Reviving a Dead IndianPosted in How To: Engine on April 1, 2015
This story began about 104 years ago. Well, OK, maybe not quite that long ago. This story actually begins about two years ago. Trasborg was working on another couple of Jeeps, and his ’98 Cherokee ended up sitting in his yard while he worked on and drove the other Jeeps. Then, the Cherokee needed to go to a show, and when he went to start it, nothing.
No big deal—jump it and drive it, right? Once we put on the jumper cables, it would crank but still not start. It sounded like it wanted to start with a few backfires through the intake or exhaust, but it never did actually fire. That was really weird because it was acting like the timing was off. However, the distributor is in a fixed location, and there was no way it could jump a timing gear tooth sitting there shut off in the yard for months. Even if it could, it should be backfiring the same every time. So, we decided it must be an electrical issue. Sitting in a yard for five months on dirt could let a lot of moisture come up from the ground under the hood.
The Jeep had 258,000 miles on it at the time and in all the miles we put on it, we never replaced the distributor, so we decided to start there. We popped the cap, pulled the rotor, and found the distributor filled with oil to the cam sensor location. Last time we checked, we were pretty sure that a distributor shouldn’t have oil in it. We knew the sensor didn’t need oil. So, we started looking for a sensor and distributor.
We found out really fast that, locally, the parts would cost us around $300. The problem was, while the distributor was obviously worn, it ran when we parked it. So, we didn’t want to blow all that money for what basically amounted to an oil seal. We found a new distributor at Rock Auto (with the sensor) and a new cap and rotor for $60. Sold! We dropped the new distributor in, and it didn’t even backfire. Hmm. We put the old one back in, and it started backfiring again.
Long story short, we tested the sensors with inconclusive results; the numbers were dead-on with some and erratic with others. So, we took another Jeep we had sitting there that was running, and just for grins, we swapped sensors back and forth. No change. At that point, the only electrical thing that made the engine run we hadn’t swapped was the coil. We were running a DUI coil and never had problems with it in the past, but nevertheless, we had the old coil from this Jeep on the shelf, so we swapped coils too and still no improvement.
We got to thinking that maybe some combination of worn electrical components combined with worn engine mechanicals allowed the Jeep to keep running. While we didn’t really think that could be it, we started checking mechanicals. We checked to make sure the timing chain didn’t jump (it didn’t). We then popped the valve cover to check the lifter arms to make sure we hadn’t bent a rod or rounded off the cam (we hadn’t). At that point, totally second guessing everything we knew, we got to thinking maybe we installed multiple distributors wrong. So, we pulled the distributor cap while we had the valve cover off to match number one position on the rotor with TDC and the timing mark on the engine. Guess what? They all matched up.
Now, even though we can identify a lot of 4.0L sensors, starters, and other random parts out of the Jeep by eye, and know what a lot of the bolt sizes in the engine are off the top of our heads, we know we don’t know it all. So, we started making some calls to people smarter than us (not hard to find). We all ran through the same kind of things and each time ran into the same dead end, short of taking the engine apart. Finally, we called the guys at Jeeps R Us in Laguna Hills, California. After talking it out and hitting the same wall and running out of ideas, they just said, “The hell with it, bring it down, we can fix it.” So, us being us, we said, “Um, you just ran out of ideas, how are you going to fix it?” They said, “We don’t know but bring it down. If we can’t fix it, we shouldn’t have this shop.”
Well, we gotta respect a shop that puts its money where its mouth is, so we loaded the Jeep up with all the parts, sensors, distributors, and other parts we had onto a trailer and set off. Here’s how it ended up shaking out.
It just goes to show you that no matter how much you know, you never know enough. Two coils died on us from just sitting there. Not only hadn’t we had that happen before, we’d never even heard of it happening before. We got so frustrated with it we were perfectly willing to pull the entire engine apart to find the problem. Sometimes it is better to just take a step back or get fresh eyes on the problem. So, thanks to Jeeps R Us for their knowledge and fresh eyes.