Edit: 1999, 4.0, AW4

Yesterday I welded up the gouges on my knuckles. I completely meant to disconnect the battery but forgot before running the first bead. Ran about 2” of bead with the ground clamped to clean metal just inches away.

Today the Jeep won’t start. Clicks rapidly, and the voltage gauge reads just over 9V with a check gauges light on. No check engine light. All other electronics work fine. Putting a multimeter on the battery reads ~13.3 V and hooking up jumper cables did not help.

Did I make a big mistake and fry something? Where should I begin this diagnosis?

 

Did you jump the starter solenoid or jump the battery?

 

Jumped the battery, like you would when leaving interior lights on all day. That’s what I initially thought I did.

 

Jump the starter solenoid. It should turn the engine over.

 

The battery reads 13.3 with the engine off? That is a little high i think. If it won't jump like that, there may be something wrong with the PCM, they can be sensitive.

 

I bypassed the starter solenoid and got nothing other than a few sparks, however, for whatever reason, my voltage gauge came back after doing that and I was able to start the Jeep and drove it around with no issues.

I have no idea what happened or why. Anybody have an insight?

 

It appears as if I'm not out of the water yet. When I turn the key to the on position the volt gauge comes up to the proper 12-13 V range then after a few seconds drops to 9 V and shows check gauges. The first time this happened I was still able to turn the Jeep over and it started no problem, even cranked pretty strong. After working in the Jeep with the doors open for awhile and draining the battery down to ~11 V it would not start. Slow turn over and rapid clicking once again, most likely because I ran the battery down. Jumped the battery and it fired right up. I let it run for ~15 minutes and am now eating lunch while the Jeep sits for a few. Gunna go try to start in a couple minutes and see if it shows any symptoms.

 

alternator diodes arent that keen on welding spikes, I would check out that

 

Agreed, and hope that's all it is.

This thread should be a sticky, so every time someone posts, "Oh, I do that all the time and never had a problem!", we can point people to what CAN happen.

 

After lunch I turned the key to the on position and the volt gauge did not drop. I did not experience any issues for the rest of the day after starting the Jeep several times and going through periods of running and sitting. We'll see what tomorrow brings. If I find I have issues I'll check the diodes.

 

FYI alternators arent meant to fully recharge a dead battery. Battery charger might be a good purchase.

 

Put a multimeter on the battery terminals while it was running to measure the AC voltage. Measured like 30 V. Crap. I then measured the AC voltage with the vehicle off and it measured like 26 V? I did the same to my other car and got similar measurements. I think my cheap multimeter may have defaulted to mV but didn't show it on the display. Anyway, I went to the parts store to have them check it with their meter and it measured 61 mV ripple voltage. Woo! No bad diodes.

I have had no issues with the voltage gauge dropping to 9 V recently. However, on startup the gauge will drop from ~13 V to ~11 V and show check gauges for a brief moment before assuming normal operation. Gunna have to keep an eye on it.

 

Yeah, the PCM is connected directly to the field windings of the alternator because it's the voltage regulator.

 

[QUOTE=XJlimitedx99;3559459]Put a multimeter on the battery terminals while it was running to measure the AC voltage. Measured like 30 V. Crap. I then measured the AC voltage with the vehicle off and it measured like 26 V?
OK now things getting crazy, yes I think your meter has died. I vote with the alternator diode popping. When my alt went, it would intermittently only charge..also at 9 volts which makes the Check Gauges light come on. I vote to check the alternator at a big box store by a competent person, in the vehicle.
I have welded with the battery connected every time I ever welded, never had an issue not could I see why I would. The welder is not part of the circuit, but, I suppose if the welder wasn’t grounded well the hot stick might exceed the peak inverse voltage rating of the diodes. So! I won't be doing THAT any more.

 

I know that it was Accidental... But I think the point here is just don't do it regardless of whether or not other people say they have.