Bizarre Electrical Issue

[Virtual TWiT]

2007 4Runner SR5, 6cyl 4.0, 4wd, just over 72K miles, brand new 130A rebuilt alt, 6mo old 31M Diehard deepcycle AGM.

I first noticed a flicker in the lights about two weeks ago that was intermittent. I can also hear the "static" of the varying voltage in my radar detector's speaker. It's not flickering all the time but while it's flickering if I shut off the engine (key to off position) the entire electrical system _sometimes_ shuts down completely, including the dome lights. This has increased in frequency the past week. If I turn the key back on with it in this condition the dash indicator lights barely glow and the voltage meter I put in (connected to the map light/overhead console v+ which is controlled by a processor) reads the system voltage anywhere from 8.o to 11. VDC. While it's in this faulted condition and the key is turned I can hear the relays in the main (engine compartment) clicking and sometimes buzzing like a coil isn't getting enough power to close the relay. I suspected a bad EFI relay and swapped it with the one next to it with no change. All fuses are good and so is the short pin. Battery connections are spotless ( I keep the engine compartment in better shape than the rest of it).

Most of the time I can pull the neg. battery cable, wait a while, then attach it and sometimes the fault clears or sometimes I have to repeatedly disconnect and reconnect it several times and then the dome lights will come on and the system is fine for a while and the whole truck runs normally. Then with no rhyme or reason the flickering comes back and starts the whole process over.

Another clue is that I was working on it just now, the whole electrical system was only showing 10VDC and nothing was on, not even the dome lights. Both driver's side doors were open, the key was in the switch but not turned and I closed the rear door and the system came up to normal voltage and the dome and map light came on.

A battery/alt tester indicated the alt had a bad diode and was only putting out <30A. The alt was replaced yesterday but the problem persists. I changed the battery and the issue is still there. The ground points on both fender wells are good and secure. I have _not_ checked the engine ground connection at the block.

I'm suspecting a bad controller unit somewhere since a dead short in the system would blow a fuse. I also suspect the Viper remote start relay but have not bypassed it yet.

Does any of this sound familiar?

Thanks for your time!

 

[mrpurplepenguin]

Another clue is that I was working on it just now, the whole electrical system was only showing 10VDC and nothing was on, not even the dome lights.

Where did you measure this, at your map light voltage meter or across the battery terminals? If it's across the battery, a load capable of dragging a healthy battery down to 10V should pop a fuse in short order. If it's at your map light meter you might try probing various circuits with a multimeter the next time this fault occurs, and see what is and isn't seeing a clean 12V.

You already checked your battery clamps and fender grounds, but definitely check the engine ground and double check the others as well; poor grounding can cause all kinds of problems. I don't know if there are any other grounding points as well.

 

[ghs215]

I had a issue like this in a Mazda 626...

There was corrosion on a grounding wire at the main fuse/relay box that I couldn't see causing an intermittent issue(s).

When you probe the fuse box main connectors with a meter, make sure you are using the (-) on the chaises (rust/paint free area) and then probe with the (+) on the fuse box. Do the wiggle test of the wires to see if you get a voltage drop.

 

[Virtual TWiT]

Narrowing things down

Thanks guys for the help so far and I've narrowed it down somewhat.

The battery was disconnected overnight.
I had told the remote-start to start the day before (a handy tool since I'm not an Octopus with 10' arms) and it failed to start, then I disconnected power at the battery. That leaves the Viper module in a "start-the-engine" state for when power is restored.

Today I measured the battery voltage at a nominal 12.6 then reconnected the neg. cable. The voltage almost instantly fell to 7.x VDC at the battery, the systems tried to come on and failed. Immeadiately I disconnedcted the battery (which has tested as good. If it wasn't a diehard platinum 1150 cca marine deep cycle batt I think it would have been fried at this point).

Knowing that that monsterous of a load would have blown the 140A main fuse, I disconnected the positive cable that attaches to the alt & starter, BUT left the pos cable that runs the electrical subsystems from the fuse box in the engine bay connected.

Keep in mind the remote start is still thinking it needs to start. Then I reconnected the neg cable. All the electronics inside came on, the dome lights and everything, then the starter solenoid kicked in just like it's supposed to do and voltage drain pulled the batt down to about 12VDC which is reasonable to my mind. Of course it didn't start since the starter and alt weren't connected.

Next I thought Ah HA! It's on the high-amp side and unfused. On a hunch I put it all back together normally (leaving the neg cabel off the batt of course) then disconnected the pos cable from the alternator plus disconnected the voltage regulator and taped it off really well. I reattached the neg cable at the battery, the truck came to life again and the remote start turned her over as pretty as you please and ran her off the battery (it was a thing of beauty to see my baby come to life again, let me tell you).

Next, I killed the remote start, disconnected the neg batt cable, reattached the pos alt cable and regulator connector, then put the neg batt cable back on. Everything was just like normal. I stuck the key in and turned it and the dash lights lit up like they should and then I started it up and it started and ran just like it's supposed to run. I watched the battery come up to 14VDC like it's supposed to do and hold for a while before tapering down.

I'm perplexed about what sort of intermittent fault this could be that could cause the whole electrical system to do all this. I do have a 31M battery on it and only the standard 130 Amp alternator. I'm thinking about swapping the battery out for a smaller starting battery next to see what happens.

I'm exasperated. :wtf::noidea:out:

 

[Virtual TWiT]

Quick Thought

Bad insullation somewhere along the starting system would cause what I'm seeing, including the lights flickering which could be caused by arcing.

Hummmmmm.

Edit: For what I'm seeing it would be the main alternator harness. Hummmm. The weather here isn't so good but it's supposed to be nice tomorrow. I need to take off the front skid plate and retreive the nuts I've dropped. LOL