Intermittent runs-bad/stall-prone/won't-start electrical issue

So, I have an interesting issue that occurs infrequently and usually goes away after a few minutes and doesn't come back for >1week.

BTW, this was never an issue before I swapped my battery to my trunk.

What happens is the stang starts to run pretty rough while the idle speed jumps around by a couple hundred RPMs. It stays running for a while, if idling, but the computer seems to have to work really hard to actually keep it engine running like that. When driving, and under acceleration, it seems like someone installed a Pinto 4-cyl under the hood (or even less) until the issue suddenly goes away.

The thing is, if it happens while I am driving, it is like someone is trowing a switch back and forth to turn the whole issue on and off. Sometimes it will be on/off a few times in a few seconds while it is happening, if I am driving. In a few minutes, no more issue. If I am idling, it still goes on/off, but will spend a few minutes exhibiting the symptoms, then not for a short time, then a few more minutes. If the engine stops/stalls while this is going on, I can crank the starter over like gangbusters, but the engine will not start. Then, magically, a couple minutes after pushing it out of the way of traffic, taking a look under the hood (finding nothing wrong), and then closing it again, and the car is fine and starts right up. I even get all the way home - no issues. :mad:

In addition to the running problems, there is the fact that the windows will not roll up/down, and the dome light will not turn on at all (not even dim, by eye, at night). What is really weird, is that if I turn on the emergency flashers and open the door, the dome light decides to "work". Unfortunately though, it just flashes along with the emergency flashers (not "steady on", like a dome light should be). :nonono:

There is no CEL/code, either. Even after the car idled like crap for ~10 minutes or so while I tried to get through a drive through like this.

I was hoping for some help in identifying some things I can check (when it is and/or isn't happening) before engaging someone @ $100/hr. In that light, how about what seems to work fine when this happens? The door locks work, the headlights are fine, and the radio works like normal (stock wiring to the head unit in the dash).

I don't see any problems with the wiring for the trunk mounting of the battery. Alternator, battery, and the fuse blocks involved in that are all fine. The ground for the battery to the frame in the back is also fine. The thing is, the 0ga going to the trunk has a 3/8" diameter copper conductor, alone. It is between 1/2" and 5/8" in outside diameter, actually. Since that monster is running under the dash, through the driver-side kick panel, then down the driver's side and into the trunk - I wonder if sometimes it might push/rub other wires in that area and cause an intermittent short/disconnect.

Also, a note on the battery relocation details. The stock wire from the alternator still goes to the stock location (that power distribution fuse block's ring terminal, IIRC), but now the battery has a new 0ga wire that connects it directly to the alternator from the trunk. Right before the move, the voltage at the battery terminals (w/ the engine running) was 13.86v. Right after the move, the voltage I got was 13.82v. I think it is fine back there.

What really kills me about all of this, is that there is no fuse that is ever blown, and it will just start working again after a bit.

Ideas? Thanks in advance, guys. :nice:
 
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If I had to bet money I think you have a shorting wire issue/bad ground somewhere. Check your wires for the trunk mount battery and trace them out. A shorting wire should blow a fuse but the crazy electrical issues is definitely a bad ground and that will be intermittent if the ground is loose or not getting good contact. Cleaning the area you grounded the battery with sandpaper and see if the takes care of it.
 
You know, it happened yesterday on a side street and I noticed that the odometer display was cutting in/out. Does anyone know what circuit off the fused distribution block this is powered off of?

I am thinking I would like to trace out some of the stuff under the dash related to that circuit, see if that giant 0ga cable I have under there screwed something up.
 
If I had to bet money I think you have a shorting wire issue/bad ground somewhere. Check your wires for the trunk mount battery and trace them out. A shorting wire should blow a fuse but the crazy electrical issues is definitely a bad ground and that will be intermittent if the ground is loose or not getting good contact. Cleaning the area you grounded the battery with sandpaper and see if the takes care of it.

+1

If you had a shorting out issue, most likely you would be blowing fuses and you would run into things that just dont work at all, but it is still possible.

IMO you really need to make sure you have good, solid grounds. If the contact is just so so, or not quite tight enough, this is the kind of crazy stuff you will get and especially with a big body ground like you mentioned.
 
Well, I can't argue that checking/redoing the main grounds is a good idea - it certainly is.

The thing is, the first time this happened was after I ran the 18ft 0ga cable through from the engine bay to the trunk. That was before I even connected either end to anything. So, the first time this happened was a little bit after I had run that 0ga cable, but before I had connected it to anything (it was coiled off and secured under the hood, and taped up in the trunk). I had had made no changes to the stock stock setup at all at that point.

I am pretty sure there is something that the 0ga cable is hitting/rubbing, likely under the dash or in the kick panel, which has started all this.

Under the dash is also where the guy who did my alarm put the brain, and it has a connection issue. However, the alarm's issue is a couple years old at this point (doesn't flash the lights while chirping anymore - did, then didn't, then did again, then hasn't from that point on).
 
Woo-hoo!

View attachment 330002

There was a loose ground in the trunk.

It was on the left side, the opposite side from where I put the battery. It seems that when I bungied my plastic gas "can" (I have almost run out of gas on a couple occasions) to a protrusion over on that side of the trunk, the action of the gas-can moving around must have loosened that ground connection pretty quickly. As it turns out, I attached that gas can at the same time I ran the 18ft 0ga wire to the trunk. This is why the issue seemed to start with the install of that giant cable. When I took out the carpeted floor panel to route it, I removed the left side trunk interior piece in preparation for some other work, later on. When I saw that I could bungee the gas can to the hardware back there to keep the thing from sliding around the trunk, I did so. Turns out that was a mistake. :notnice:

I am still stoked, as I just found it on the side of the freeway on the way back home. I had all my tools with me, as I was going home after working on the car in the driveway of my Aunt's house. I just whipped out the right sized socket, an extension, and a ratchet - then went to town. I work on my car at my Aunt's house so that my fellow apartment-dwellers don't see what I do to it, and also because working on the car in the apartment complex's parking lot is technically a no-no.

My electrical issue had started again, right after I got on the freeway headed home. Love those on-ramps. :D This time, I even had my Digital Multi-meter on hand. It turns out that I didn't even need it, though. It is really dark out this late, and so I could actually see a little arcing on a ground connection off to the left when I opened the trunk. My "temporary" MDF subwoofer box had swung around and hit the gas can during the on-ramp, since the 'can is bungied to the left side. I try to keep the box secured, but it weighs a ton (the reason it is only temporary), and it doesn't like to cooperate with the couple different methods I have tried (so far) to keep it stationary. When it swung over, it knocked the gas can, which in turn knocked the ground into a position where it made no connection, or at least a really-crappy one.

The ground in question is normally hidden by the trunk's carpeted interior piece on the left side. I have that side and the carpeted floor panel out ATM. I'm going to be fiberglassing a "permanent" subwoofer enclosure back there, as soon as the weather holds up long enough.

I really think that was it. It fits as to when this all started, as well as the intermittent nature of the problem.

:nice: