scifi266

First post on this forum, Usually working on trucks.

I'm working on a 1990 Jeep xj, The 4.0 liter straight six, with a 5 speed manual transmission.

The issue that I'm having is that when the battery is fully charged, the jeep will start. After about a 6 mile drive, it won't start. It tries to start but it goes down until it acts like the battery is dead. This is only after three attempts. Attached a fluke meter, and the battery reads 12.5v so it's at full charge. When going to start it drops down lower and lower til about 3v. Let it sit and it goes to 12.5v in about 2 minutes but it won't start the jeep.
I've replaced the battery clamps, cables, added another ground. I don't know what it is. Replaced the started and that didn't seem to help either. The alternator passes at the parts house. It also puts out 14.5v when running, so i'm pretty sure it isn't the alternator. I just can't figure it out and it's driving me crazy.

Thanks guys, I look forward to learning all i can about jeeps from you guys.

jinxfactory

Have you checked all of your grounds? Sometimes this could cause excessive draw.

skud007

How old is the battery? also is there enough water in it if its not a sealed type? could be a bad cell in the battery.

scifi266

Well we've checked the grounds and they're good and solid. We have the same problem even with another battery. Really confusing(but probably simple), really need to get her on the road again.

ET JEEP

Load test the battery to see how strong it is. Something is causing a current draw. The starter would be the likely suspect but I see you replaced it. Did you go new or used on the replacement?

skud007

I was pulling my hair out trying to figure out what was wrong with my start issue after putting a new (remanufactured) starter in. Worked for about 4 starts then nothing. They can be bad right out of the box. Got a replacement since and no problems after a week. The solenoid wasn't kicking the gear out. Sounded like it was while installed in the jeep after jumping it with a wire. Took it out and had autoparts store bench test it. Passed ok. Put it back in and nothing! Checked everything else I could. . .NSS, CPS, and wiring. Pulled it back out hooked it straight to the battery and no action! Just dont want to see someone go through what I had too!

scifi266

Hmmm, might have to get a new one then. This starter sounds strong when it's going with a full charged battery. I just don't get why after driving after ten minutes for about ten miles that it acts like it has no charge. The meter says it has a full charge, and that the alternator is throwing out 14.5 volts. It's just driving me crazy, I don't get it. Where else would it draw from? When it's cold it starts right up, after a warm up drive she stops. Let her sit for an hour and she starts again.

ET JEEP

You may have a problem with the starter that is being affected by heat. When it is cold, it starts up and after warm up something breaks down. When you are starting, the starter is the only high amp draw item that is running.

scifi266

Well the battery passes at the parts house too. this is just getting me mad lol

scifi266

Alright, decided to keep the jeep running on a charge the starter would would get her started at. Drove her non-stop for over 30 minutes. Hit a hill and she started to struggle, Hit a stop and she would barely start going again so I stopped her, threw another battery in and she was fine. The pulling was the alternator, or at least I'm pretty sure. At Idle the alt tests fine, but i'm pretty sure that under load it isn't doing a damn thing. Going to test that next.
Let me know what you think.

ET JEEP

Do the test again. When you get to the point where she is starting to struggle again, disconnect the alternator from the system. If it starts normal the problem is the alternator. Tape any cable you disconnect to isolate it from contacting anything.

Also test battery voltage at the start and again when she bogs down. See if there is a difference in battery voltage. If battery voltage is down, then the charging system may have a fault.

If you have a helper, check the battery voltage drop during the starts.

This sure is puzzling.

scifi266

Got it finally, been running her for a week with no issues yet. We put in another starter, added another ground to the block, a ground to the starter, and an alternator and she seems to be running and charging great.

However, now I have doubts about testing equipment at parts houses.