Can't get Jeep to start

Here recently, I have been having difficulty getting my Jeep to be reliable.

Last week, it refused to start, so I pulled the battery and went to Les Schwab to have them test it. Well, the battery cell was fine and they said that it was fully charged (had been on a trickle charger for a while).

Well, I get it back to the house and ask my roommate for a jump and sure enough, the Jeep fires up after having tried earlier in the week doing the same thing minus the Les Schwab trip.

Today, after it having functioned properly all week, it wouldn't start. It'd try to turn over, but it just wouldn't fire up and keep going.

I replaced the alternator last October along with buying a new battery. The starter works fine because it is trying to start. I haven't had a tune up in a while, so is it possible that I need to give it a tune up? I bought new plugs for it when I got the battery tested, so I can do that right away. Is there anything else that I should check before I give it a tune up?

Anyone else had this problem? What would some suggestions be? I don't want to have to shell out some bucks for a shop to do it. What would a quick tune up regimine be for my Jeep?

I went to Schuck's and bought a new TPS sensor and that didn't help. I'm at a loss and figure I'm going to have to take this to a shop now.

Thank you for any and all help.:clap:

Year/engine/trans and any other info would be helpful.

So it cranks plenty fast but won't fire, or does it crank slowly but won't fire?

Whatever you have, gap (0.035") and change the plugs. If you have a '99 4.0, I think you may have the coil rail. If you have the cap, rotor and wires, you probably need to change them too. Dielectric grease to seal the coil rail boots or wire connections is an extra positive to seal out moisture. When you pull out the old plugs, keep them in order front to rear so that if you see a difference in color (like one is darker than the rest), you will know which cylinder (wire, injector, etc.) to diagnose.

99 I6 4.0

Cranks plenty fast, just won't actually "start". I wish I had better knowledge of the subject so I could describe it better.

I think it will be visiting the shop on Monday to figure it out for sure. I just don't have the time as I have a job, lacrosse practice and college that I have to go to.

Did you put those new plugs in that you purchased? Only takes a little of your time. After that, it's time to freshen distributor cap, rotor and plug wires. BTW, there isn't a coil rail on a 1999. That started in 2000.

Gotta eliminate tuneup hardware as a cause before moving onto other more complex causes. If there is a check engine light, you must pull the codes for a clue.

If after tuneup hardware is changed out and you're still symptomatic, it's time to test fuel pressure and test spark quality. If that's something you can do yourself or have a shop do has to be decided by you. Testing is the only efficient way to get to root cause.

First check for spark. Pull a plug and rest it on a nearby bolt ensuring the electrode/threads are being grounded. With it hooked up still to dist. via your SP wire, have your roommate try to start it. There should be an obvious spark.

Let us know what you find as the next diagnosis is a bit more tricky.