3.4 auto voltage drop when shifting into reverse/drive.

I see 4 heavy ga. power wires all drawing off 1 battery. Are you supplying enough juice for everything you have running?
I know of guys using marine batteries as back ups when running big audio.

 

So there’s nothing extra running and I’m not an audio guy. Technically my projector headlights are an extra wire along with my winch. The other two are the fuse box power wire and the alternator power wire. Not to mention the behavior is identical after swapping back to stock wiring.

My 1999 has the same exact setup and handles it fine with it’s weaker (but higher than stock) 105 amp alternator. I’ve also done this battery cable upgrade on multiple other Toyotas for friends and it’s always been fine.

 

So I've put it back in and it doesn't raise the voltage up as high as it used to. It barely hits 14.0 with it installed when I used to sit at ~14.2-14.5 before the engine removal. I've installed the Mean Green alternator and AGM battery in my 1999 and it sits at ~14.3 steady no matter what. That's without a voltage booster because it's an upgraded alternator with a different voltage regulator than stock from what I understand.

The reason I'm concerned to drive it is the behavior when I'm driving. I'll be coasting down an exit ramp and see some uncomfortably low voltages like 12.1 or 11.9. I've also seen it shoot up to 16v+ when I tried running my stock alternator for a bit. The blower motor (and I assume the headlights/taillights) are also pulsing up and down whenever I'm in stop and go traffic in drive. So essentially I no longer have functional air conditioning in stop and go traffic.

Here is the behavior of my truck in 2021 which is identical to how the truck behaved before I pulled the engine. I'm really hoping to get back to something remotely close to that. I'll continue the voltage drop test on other cables and grounds later this week when I have my new voltmeter cables.

And apologies if I sound aggressive, I really appreciate the responses from everyone.

 

Not at all. Completely understand, been there before. Frustrating as hell knowing your own truck and something feels wrong but can't figure it out.

 

We have all been there.

Something is different since you installed the engine finding out what will drive you crazy.

Crushed wires

poor connections

something loose that flexes .

I know how often I have been distracted pulled away and forgot something or left it finger tight.

It seems to always start and keep the battery charged . It happens with different Alternators and batteries.

To me that tells me the charging system is really not the cause .

Might be the reaction of the scan gauge is so fast a normal voltmeter would not react at all.

In theory the battery should be taking up those little power changes as loads are added and removed.

I would love to be close enough to help in person

why I hate automatics

 

The voltage should never be anywhere near 16v… you have a regulator problem. 14.2 maybe 14.5 at max amperage output.

 

Exactly. The 16v situation is the reason I refuse to drive the truck. All three alternators I have in my possession work fine on my other 1st gen Tacoma. I’m going to blame the truck and not all three of their regulators. Having another 1st gen around to test things has been nice.

Got the clamp voltmeter cables in and I’ll report back with any findings.

 

Eeek… this is gonna take some time… swapping out fuse boxes would be a pain but having said that, there is a large amperage bolt in fuse, how is that connection? We could be chasing our collective tails here and it could be something so simple like the trailer adaptor or ?

 

An extra set of experienced eyes is always good.

I have looked at really simple things but the brain keeps saying everything looks good.

Good luck!

 

My truck was not equipped with a hitch or any trailer wiring. I added a Hopkins brand one in ~2018 that was inline with my tailight connectors.

As for fuses. I’ve disassembled/split the fuse box so I can go over those connections again pretty easily. The behavior existed even when I bypassed the alternator fuse originally.

 

This is from the 1998 manual, if it is redundant, sorry

 

So I have an 03, 99, and a few other year manuals. I'm just going to be honest and say I don't even know where to start. Truck acts completely normal besides at low RPMs in gear like at a stop light. I've done a voltage drop test on all the grounds with the truck running and I've replaced most of the cables back to stock. If I couldn't install the stock cable I tried multiple different cables.

I put back in my stock alternator yesterday and it instantly shot up to 16v. My currently installed Mean Green makes awful noises and my flatbed's alternator isn't coming out again for testing. So I've ordered a Denso 150 amp that's drop in ready for the 5VZ. I'm just curious what it will do when installed.

I'm not throwing parts at the problem if I have no properly functioning alternator for the truck and need to get one regardless.

 

Best of Luck!

Are you sure you had no electrical issues before pulling the engine ??

I would have left the brand new cables on. Maybe you feel the quality of the new cables is sub par and they were a complete waste of money??

Waiting to see the successful finish of this.

 

So the truck is relatively low miles and had 100% stock battery wiring before the pull. I have video footage of the voltage taking no hits with AC on in the summer and heat on in the winter. The blower motor bogging down at stoplights and other behavior just wasn’t present before.

My concern is that these battery cables are somehow not crimped properly. The big three, 7, etc. upgrades have been well worth it on the multiple vehicles I’ve installed them on.

But it wouldn’t be the first time I’ve received a badly crimped cable from a reputable vendor. Since my old battery cables were fine I’d rather have them installed right now while troubleshooting.

 

Simple to test for a good crimp put the lug in the vise give it a good tug .

I crimped many cable lugs .

The best one I ever saw they never removed the insulation and crimped the lug over the insulation .

Could not figure out the no output problem.

Good luck !!

 

This is exactly what I used with a mini sledge, no issues at all. Used it when I did my +/- 2 AWG run to the bed of the truck. Used it when I did the engine bay grounds, building out the RTMR, all of it.

Not as fancy as some of the other options but if it works, it doesn't need to be fancy.

$20 Forney 57637 Lug Crimping Tool, Blue

https://www.amazon.com/gp/product/B003X51S00/

 

I probably missed it before and sorry if I did but, can't you swap in the old cables? I know its a PITA but at least then you could rule out the cable aspect. As for the questionable vendor, I'd crimp them myself. You would know it was done right by doing it yourself.

If they weren't crimped properly, I'd think they would have an intermittent bad connection instead of voltage shooting up.

If there is any doc you think you need, let me know and we'll dig it up.

 

Funny you should show this I built a frame to use a 4 ton jack.One day when I was bored.

I was not fond of using a hammer.

Then I up graded to my Good crimping tool.

 

I swapped back in my stock cables other than the fuse box to positive battery post cable. Because I had to cut that one since it's shared with the ABS2 fuse power wire. But I still tried 2 different aftermarket cables to the fuse box to make sure that wasn't the issue. And you're right on the intermittent bad connection. I just saw nothing else to troubleshoot so put the old ones back in out of desperation.

In theory the voltage dropping at lower RPMs sounds like it HAS to be a voltage regulator problem. The alternator connector could be damaged too I guess.

 

Ohm out the battery light circuit. If that circuit has excess resistance that can mess with it. I'd also replace the charge light bulb too.