Electrical problem, voltage...

I apologize for the block of text, this is my story:

Drove home from WV to NJ, thought the alternator might be going out so I bought a spare for the trip. The GEN light was on and the voltage would be between 12 and 14, sometimes revving high would raise the voltage enough to get it to stay towards the 14 mark, once it was at that mark on the highway it wouldn't move. Driving on back roads with changes in rpm/gears, towards the end of the trip, never went above 12 again.

Several hours later we changed the alternator, GEN light still on and voltage went up after letting the Jeep idle for a bit, but then upon driving voltage dropped back down to 12. Drove it a bit more and eventually the guages dimmed and started failing so I pulled over. Then replaced the battery to get it home. Took a meter to the battery and it was at 12.7 with the engine off. The alternator was putting out 11.4 at idle.

I was then going to rev the engine to see if it got higher and my friend was reconnecting the multimeter to the alternator when something sparked and the Jeep died. Now the Jeep won't turn over at all. No fuses in the engine bay were apparently blown. I've heard to check grounds but I don't know where/how/what to check for? Starter is engaging and it sounds like it wants to turn over it just won't finish. Check engine light is on and I'll post the code later. When turning the key to the on position the lights do come on and everything seems normal.

Ok, sounds like the batter(ies) are dead.

First step, disconnect and fully charge the batter(ies) for 8 hours (good) or 24 hours (best).

While the battery is disconnected clean BOTH ends of both cables. While you have the cables disconnected to clean the ends test the cables with an ohm meter--resistance should be near ZERO.

Ok, good time to also renew all of your grounds--you already did the battery ground to the engine block when you cleaned and tested the negative cable. There is a strap ground at the rear of the head, driver's side, that provides the OEM unibody ground to the firewall. The straps degrade rapidly and are problematic, replace with a short cable. Adding a battery to fenderwell ground is always a good idea.

Ok, now that the batter(ies) have been fully charged have them load tested. If they both pass then just choose one and reconnect it. Check the static voltage between the terminals, should be about 12.5. Reconnect the cables and see if it will start. If it starts, then recheck the power between the battery terminals, should be about 13.6 to 14.5 volts. If not, then then you have an alternator/regulator OR alternator/PCM problem.

You didn't specify the year of your XJ. Please always do so in the future. Early XJs used GM type alternators with internal regulators, later XJs have Nippondenso and the charging is controlled through the PCM.

Read this article for good info on upgrading your cables: http://www.olypen.com/craigh/charge.htm

Turned out to be a blown fuse, somehow I missed it when I checked the first time. Started right up afterwards. Driving it with the new battery/alternator led to no GEN light, but I noticed the voltage sits low until I start moving. I'm going to get the batteries load tested tomorrow. Thanks for the help.

I know this may SEEM like a hijack but it's really not since I'm having a similar issue that I'm trying to fix using the plan in this link.

http://www.olypen.com/craigh/charge.htm

I really have to preface this with the fact that although I'm pretty good at problem solving, electrical issues give me a brain cramp.

I'm half way through doing the upgrade on that link (thanks again joe_peters) BUT when I get to the part about the alternator input to the starter relay and the big mega fuse. What is the amperage of the starter relay? If it's not over 100 amps what is the point of putting a 100 amp fuse in-line on the alt feed wire? It would never blow before the relay was fried, right? Am I totally off on this?

Just making the battery to relay wire bigger (I went with 4 ga. cable) has made an improvement, yet it's not completely solved so I was hoping doing the other half (alt to relay) would finish it off. I'm leery about putting the 4 ga. to the relay without some sort of fusing.

Can somebody straighten my head out? When I went to get the mega fuse the owner of the shop told me it would not make any difference to upgrade the wire unless I ran it to a buss box and ran my accesories through that.

More power needed.

Interesting point.

You are replacing a fusible link 10 ga wire with an unfused 4 ga cable. The author recommends using a fuse that is at least equal to the alternator's output.

That brings up a number of questions:

1. What is your alternator output current and/or planned upgrade?

2. What is the rating of the fusible link in the OEM 10 ga wire?

3. And as ParadiseXJ asks, what is the rating of the starter relay?

I actually don't know the rating of the starter relay, but that may not matter at all. My thoughts on this is that the starter relay simply has a large lug on it for the power distribution, and that the lug has no relationship to the relay function of the starter relay, but is simply a "manufacturing convenience" eliminating the need for a separate junction block. Anybody have toasted starter relay they are willing to tear open?

Now what about the fusible link on the lead from the alternator? Well, in the FSM 90 it discusses 4 different output alternators, 2 for the 4 cyl. and 2 for the 4.0; the highest output of the four is 100 amps. I am going to make the assumption that the author of the article based his minimum 100 amp fuse on that factor, as it would make sense that the dealer would only stock one cable with fusible link, and that it would be the cable of handling the largest load. Just spit-balling here, but that could be reasonable. I am guessing that the upper 250 amp fuse would account for the easy upgrade of putting a 200 amp CS-144 alternator in the XJ, with room to spare, but what is the highest output alternator you could possible mount, or what is the max output that could be achieved by any alternator you could possibly modify and mount?
Any of this making sense? I have a headache.

Anyway, if we a**ume that the PDC lug on the starter relay is just a junction block built into the relay for simplification, that would mean using a fuse with the 4 gauge alternator cable that is cable of handling the max output would be appropriate.

Resistance tests are nearly useless on charging system concerns. Try voltage drops instead. With the circuit in full operation (running, lights on, blower on high, etc) set the meter to VDC and put the leads on opposite ends of the same cable. It should read no more than .5V, or there is power being consumed in the cable by high resistance (which doesn't show up with an ohms test).

Do this on the positive and negative cables both. It also works to check slow crank/ starter issues.

joe_peters said:

... Adding a battery to fenderwell ground is always a good idea...

Click to expand...

Why would this be advantageous?

joe_peters said:

Interesting point.

That brings up a number of questions:

1. What is your alternator output current and/or planned upgrade?

2. What is the rating of the fusible link in the OEM 10 ga wire?

3. And as ParadiseXJ asks, what is the rating of the starter relay?

...Any of this making sense? I have a headache...

Click to expand...

Like I said, brain cramp:doh:

JJacobs said:

Resistance tests are nearly useless on charging system concerns. Try voltage drops instead. With the circuit in full operation (running, lights on, blower on high, etc) set the meter to VDC and put the leads on opposite ends of the same cable. It should read no more than .5V, or there is power being consumed in the cable by high resistance (which doesn't show up with an ohms test).

Do this on the positive and negative cables both. It also works to check slow crank/ starter issues.

Click to expand...

Granted, I'm just going off my gauge, I have not broken out the DMM yet. I'll take an Advil and check these values tomorrow. The voltage drop on the gauge is what's been disconcerting (that, and the slow blinker speed, the headklights, dash etc. all seem fine.

Tomorrow's another day. Thanks

As the author stated in his article, and I have held this belief for many years, you can NEVER have enough grounds. Without adding an extra ground, at least on the early XJs, everything in the unibody that grounds to the unibody has to run through that single ground strap. Adding another ground to the unibody just seems prudent to me.

joe_peters said:

As the author stated in his article, and I have held this belief for many years, you can NEVER have enough grounds. Without adding an extra ground, at least on the early XJs, everything in the unibody that grounds to the unibody has to run through that single ground strap. Adding another ground to the unibody just seems prudent to me.

Click to expand...

That makes perfect sense now that I think about how many times I've grounded something to body sheet metal and called it good. Having an actual battery ground that doesn't have to go through the block down a greasy strap might make some of my accesories work better too. Consider that part of the project. I already have a shiny spot picked out.