'86 22RE auto 1 ton 2wd cab and chassis DLX dually (was once a motorhome)

I'm ready to give up as of rewriting this. I've been stuck for days past when I was supposed to leave, I have no idea what's wrong, and I'm six seconds from pullin' a whistlindiesel on my former favorite truck.

Here are the symptoms:

80A fuse blows right after engine startup *but not beforehand*
engine will then run until shutoff
loss of instrument panel, signals lights, radio, brake lights, and anything downstream from that 80a fuse as of starting the truck; fuel pump works, headlights work
unable to restart because the 80A fuse is blown and there is no power to ign
the 30A and 40A fuses are totally intact

Diagnostics:

I'm seeing <5 ohms resistance to ground when reading from the white wires on the 80A link but only with the ignition "on", saw 3.3 ohms from black and yellow wire below the column to ground
Removing the "engine" fuse in the panel removes this connection to ground. Not sure if that's my issue.
Confirmed alternator and battery side wiring do not have shorts to ground - with ign off I see no resistance to ground on either side
80a fuse still melts whenever it's started

Repairs:

Replaced fuse, obviously that doesn't work long
Cleaned all grounds and positive terminals. They're good

Outcomes:

Symptoms persist. Cabin electronics work and the fuse holds out until the engine runs. Then I'm back to square one: a dead 80A fuse and unable to restart.

Other recent changes:

New battery, alternator, and belts after the last one failed. The 80A fuse did ever blow not until I put the new alt in and started it with a fully charged battery.

Other data:
12.9V battery (no load), 12.5V battery key "on" engine off
*going to check alt output voltage next*

Looking for advice, motivation, whatever. I'm normally a heck of a mechanic, but this thing has me totally beat. I'm ready to give up.

 

resistance (ohms) is measured with the battery disconnected, not with the key "on".

 

try this: https://www.pirate4x4.com/threads/80...blows.2215305/
and this: https://www.yotatech.com/forums/f116...t-fuse-310756/

looks like both cases were bad alternators, and you mentioned that this started when you replaced the alternator? it looks like people are saying that the 80a fuse is for the alternator.

 

wallytoo, you misunderstood. The battery was out. I had connected my negative lead to body ground and my positive lead to the AM1 connection. With the key off I saw no loads. Turning the key on to check for shorts in the IGN circuit showed 3.3 ohms from AM1 to ground. That would only draw ~4A with the battery in and is not my problem. Days of reading this forum indicate that's a normal number. At least one other guy chasing a bad alternator came up with the same values using the same methods.

osv, I suspect I blew my alternator to start with. My belt was slipping and I was running a high electrical load (wipers, lights, stereo, engine, plus an extra 25A draw on a HHO hybrid kit fed off the battery terminals) for a few hundred miles. When I hit city traffic and the revs dropped, it stopped charging.

As for the fix... I replaced the 80A fuse with a circuit breaker this morning. Turns out, I didn't need to. The alternator shorted out internally on the last test fire. I now see .1ohms to from the top terminal to ground with the white wire disconnected. That's what as popping my fuses. Thank goodness for those "lifetime" warranties, right?

How many times do you guys think I'll have to do this before I get a good one? I'm not even going to put the cooling system back together until I've test fired it breifly. I'm losing a lot of time by trusting the new parts are good parts.

 

you can test for an internal short in the alternator, so at least you can try that on the new alternator, before taking it out of the parts store, although i'm guessing that the it died after it was installed, which is what i think that you indicated.

maybe leave the hho hybrid disconnected until you get the truck back home? keep us posted how it goes.

there used to be places to get higher amperage stock alternators... i put a 150 amp one-wire gm alternator on my truck, for a future winch addition, but it was a hassle.

 

When you return the bad one, ask them to put the replacement on the test machine. Good luck.

 

not really. you failed to make any mention of that in the post. we aren't there; you are. we can't see what you see, we can only go by what you write.

glad that you narrowed it down to the alternator. if you have a lifetime warranty, that's probably a good investment with all the chinesium that's in stuff now.

 

My apologies if that came off defensive wallytoo. Every house brand alternator is chinesium these days far as I can tell. The metal pulley on the new ones is a dead giveaway. I just paid more so I can replace it three more times for free next time it blows. Hopefully it won't so long as I replace my belt next time I run out of adjustment range!

osv, the kit has been off (and was later disconnected as a precaution) since I noticed a low battery voltage and no charging on the last drive I took. Thing was, I reminded myself I was lucky I got that far beforehand and that I should definitely take the ten minutes to do the belt before hitting city traffic. I restarted the engine instead and here we are!

Here's the carnage/outcome:

The first new duralast gold shorted through the top terminal direct to ground after three start-ups. It read 45kohms from top terminal to case before installation. It still tested good on the duralast brand tester even with a dead short to ground. Based on what was explained to me, "the testers check the diodes, rectifier and regulator." I do not believe they test for field windings shorted to ground. I suspect they use a current regulated 12vdc supply for the tests in the machines which would prevent shorted windings from wiping out their test equipment like it did my 80A fuses.

Good news is that the second duralast gold worked right out of the box. It read 93kohms from the top terminal to exterior casing before install. It also tested good on the duralast brand tester. That was not a surprise.

The OEM alternator also tested good on the duralast brand tester. Interestingly, it reads infinity/open circuit from the top terminal to the exterior casing. It also tested good! Strange... It wasn't charging at all while in the truck despite all fuses and connections testing good.

I'd also like to say, I'm glad I dug in as far as I did. I checked every wire in that truck for issues this week and besides some corroded connections, it's in really good shape.

All that said, it works again! Holds 14.2 volts happily. Amperage range was confirmed to be correct via handheld clamp ammeter at the same time.

 

Also thank you everyone for the responses and information shared on this forum. I would not have been able to go through every circuit on this trucks electrical system if it weren't for the work you folks put into sharing what you know. The books only help so much when tracking down intermittent or unlisted fault conditions.

 

i've had decent luck with duralast stuff, fwiw (not specifically the 4runners, but i have 6 vehicles on the road right now, plus 2 more that are headed back on the road). their stuff tends to fit factory connections/hookups without needing massaging. i made the mistake of gettting some off-brand for the lower BJ in my parts 4runner (before it became the parts 4runner) and the casting didn't match the mounting holes on the knuckle.

and i was saying it's a good idea to get the lifetime warranty if it's available, because so many parts do fail out-of-the-box. they don't always cost more with the warranty.

 

These both needed massaging. The pressed insert on the front side of the new alternators seem to be ~1/16" too thick. A handheld file made quick work of the aluminum inserts. I figured my filing depth by hanging it by the top bolt, setting it into the mount as far as it went, and tapping it with a piece of wood through the driver's fender well. I used the witness mark in the aluminum as my goal. Turns out, that happened to be flush with the small flange it is seated into on the alternator housing. The result was a good, solid interference fit that only required a small rubber mallet and that carefully placed piece of wood (through the fender well flap behind the steering box) to reseat when hung by the top adjustment bolt.

Having pulled alternators in and out of this truck many times alone without a jack, I'd like to note, I use a 1/4" socket extension to figure out which way to wiggle the alternator before putting the bottom bolt in. If I can feel a "lip" inside the hole on the top, bottom, left, or right, then I gently tap it the opposite direction. Once it feels almost perfect, I put in my bolt and rock it until it slips through. I'm extra careful about not boogering those threads up considering this is my third time doing this job in 10k miles and my second time doing it in 0 miles.

 

Update: still trapped. Alternator failure #3. No shorts, no wiring issues. Voltage regulator failed on my second startup. I'm gonna go ahead and say the new duralasts (even the 'spensive ones) should be avoided entirely. They are obviously chinese made.

Here's how I know: the cheap clones use a brown plastic plate for the voltage regulator (pn 126000-0400). The connecting ring where the plug goes in is brown if you have one of these cheap regulators. A bare metal pulley is another dead giveaway of a clone.

Genuine densos use black voltage regulator plates, have a black ring where the plug seats, and black painted pulleys. Some seem to be available under other brand names for as cheap as $60.

That said, I'll be "rebuilding" the OEM one I have with a genuine denso regulator and returning the duralast gold chinese edition.

 

Back with the truck. Going to give it another go tomorrow. Walked away when duralast gold #2 gave up. I'd just had enough.

Interestingly, this time it will still start up but I have no cluster lights except the charge indicator, just like when the OEM alt stopped charging. I replaced the 80A fuse with a circuit breaker. It did not blow. The alt just stopped working after shutting down from the third start / second proper run.

I'm going to double check my starter solenoid for shorts tomorrow. If the alts are blowing on start-ups, there are only so many things it can be! I'll check my direct to starter draw off the larger battery cable and all other current draw by running a clamp meter over the fusible link headed the fusebox.

Also have a correction to make, I did find some reman Denso voltage regulators and they used a metal base plate, not plastic at all!