I'm new to the forum and a fairly basic DIYer. I've got a '98 XJ 4.0 2wd automatic that will not spark. Would really appreciate some thoughts before I leave it to a mechanic to charge more than it's worth. Here's the backstory... please excuse my lack of terminology:

Jeep has just over 200k and I've done thorough maintenance and repairs as needed for about the last 30k/3 years. I don't know anything about it's history prior. In the last month, it has taken a little while to actually start. It will crank but took several seconds to turn over completely. In this time, it will intermittently do nothing when I press the gas from a stand still. This is VERY brief then catches and goes. In the last week, it stalled while sitting at a red light. It let me crank it back up immediately with no issue. Not overheated and plenty of fuel. The following day, it shut off completely while I was driving. I took a few minutes to try to start it back and it would only crank. It started ONCE but immediately cut back off.

So far I have done a lot of research and don't know what direction to go.

I've replaced the ignition coil and crankshaft position sensor because there is no spark. I tested this back putting a screw driver into the end of a spark plug connector (the rubber part) and touching it to a ground. Nothing I have done has fixed it. It has also now started making a humming noise coming from the fuse box.

I also had a the alternator rebuilt at a reputable shop in the last 6 months.

I'm stuck.. please help?

 

You will want to take a spark plug (not in the engine) and connect it to one of the wires and (carefully - rubber gloves) hold the tip to a known good ground and crank it to check for spark.

I'd immediately suspect the ASD relay if the humming sound is coming from the box in the engine compartment. Pull and test the relay and it will help you narrow down where to look for the problem if it's not the relay itself.

Have you tested the battery? XJ's are notoriously picky about battery condition and it could be as simple as your battery is on the way out.

 

Thanks for the quick reply! I'm going to be troubleshooting more after work. The battery is probably a few years old. It's the one I bought it with about 3 years ago. For a quick check, I will put my wife's battery in to give it a shot tonight. The tech that rebuilt my alternator told me the battery was aged but charged up fine. He recommended keeping an eye on it but I honestly don't know how to test one. I own a voltage tester that hasn't been opened!

But just to make sure I understand..

Remove a spark plug from the engine, put the rubber connector back on it, and then touch it to a ground while trying to start it? That's how I'll know if it sparks?

I will pick up an ASD relay from an auto parts store. It looks like they should only be around $10.

 

Nope. He means take spare spark plug (not one already in the engine) and disconnect one of the existing spark plug wires to test using the spare plug. You could take a spark plug out of the engine to do the test, but that is a lot of effort for a spark test. At auto stores they also sell special little tools for testing for spark. Worth getting one, because they are nice to have on hand. One of the coolest is a little tester that pulses light just by simply holding it next to the spark plug wire. Though it won't necessary show the quality of the spark (in terms of color and intensity) but it is good for very quickly testing for the presence of spark.

 

Hahaha, no worries - everyone has to start somewhere.

Yes, plug the spark plug into the wire (in your case, probably any wire since you're looking for spark in general rather than at a specific cylinder) and make sure it's connected (the clip inside the wire boot (that's the rubber connector) needs to be on the end of the spark plug. It should spark when you crank the starter (in other words, try to start it).

$10 isn't too bad, so that's easy enough to replace. What unfortunately happens is people get frustrated and start "firing the parts cannon" - in other words, replacing parts that *might* be bad without fully diagnosing their issue or verifying whether the part is working. It's a very understandable mindset, but it almost always results in spending waaaay too much money on things that were working fine and leads to further frustration.

I'd replace the ASD relay first, test if that corrected the issue and if not:
- Break open the multi-meter! You own an XJ, you WILL be using it. Read the instructions and/or look at some youtube videos to familiarize yourself with the operation.
- Test the battery voltage running and not running. Watch a video or two on youtube for "testing a car battery with a multi-meter".
- Check and clean your engine grounds and battery cables. Use some steel wool and/or sandpaper to clean up all the contact surfaces so you have a good connection. Use a bit of dielectric grease when re-assembling and make sure your connections are tight. You want the wires off the battery, the grounds on the fender and the grounds on the engine block near the ignition coil. There are a few more spots, but start with those.

Do the first and third item even if the new ASD relay corrects your problem.

Make sure to report back with your results - especially if you solve it.

 

Hey guys, sorry for the wait. I tinkered on and off with this thing throughout the week. The weather timed itself just right to downpour every evening when I was off. But the problem is fixed. I'm not sure if it's a combination of the following or just one in particular:

The bad relay was the ASD relay. Which, from what I read, coincidentally causes the plugs to spark. I replaced that for $18.

I also found a ground wire that the eye had completely broken off. Once I replaced the eye connector and regrounded it, the check engine code for the torque converter disappeared. I could not tell where the ground went to because it disappeared into a bulk of wires cover by that black plastic sleeve.

I did test with a different battery a few days ago before I changed the relay and ground connection with no luck. This battery seems strong still when charged up.

So all in all I spent about $200 when I could have fixed it for $20, but I guess there was no way to know since the relay wasn't making any odd sounds at the start.

Really appreciate all the help and direction!

-Chris

 

Glad to hear you got it fixed!