GeoRoss

I developed a cold no-start last week when I tried to drive home after work. I went to start and acted like a dead battery, no gauge, fan, clock, radio and buzzer. However, the dome light was dim and the rear window worked normally with the key. I'm at work and all I had was my free HF DMM (which failed LOL) and a mini leatherman tool. The symptoms led me to believe it was a fuse. I pulled and visually checked the big 30A and 40A AM fuses, visually inspected the 80A and they looked fine. I checked the usual suspects on the bladed fuses and they looked fine. I'm at work and stumped. I noticed though after pulling and checking fuses the dome light was back to full brightness. I put the key in and everything came back, radio, gauges, fan, buzzer, clock. I turn the key and it starts. Woo-Hoo! I can get the 4Runner home.

That night I recreated the problem. I turn the key to run and everything works. I go to start it and everything dies. I wiggle the AM fuses and things come back. I try to start and everything goes dead. Well this officially became a weekend project.

I check voltages at the AM fuses and they look fine. I pull the 80A and it seems fine. I check resistance and they seem fine. I inspected all the connections in the relay box and they looked solid. No wiggling, no wire damage and no corrosion. Since it looks like circuits for both AM fuses I start looking at the 80A. I clean all the contacts put it back together. I go the the F1 connector by the airbox and clean those contacts. Nothing really looked corroded. Nothing really looked out of place except I did find an abandoned trailer light box behind the airbag that was scotch locked to the tail lights in the cab . I pulled and fixed that. It couldn't have been involved, but what the hey.

Everything works now and has since last Saturday. First, I am a complete loss at the symptoms. The AM fuses were almost acting like breakers. I have no clue how to explain those symptoms.

Anyone smarter than me have any ideas? That should include everyone. I didn't do any load testing which I guess would be the next step. While I'm glad the 4Runner is working, I'm not a fan of self-healing electrical problems.

RASALIBRE

old87yota

Only time will tell if the problem "self-healed".

From the sound of your symptoms, you were temporarily losing a main power feed or main ground back to the battery.

Since you were in the area of the AM fuses when the problem comes back and goes away, I would look for a loose connection or bad wire / cable in that area.

RASALIBRE's suggestion of the fusible link is a good place to look.

The fusible link just looks like a wire with a sleeve on it going from the battery to the fuse box.

With the 4Runner now working, visual inspection may be the only way to find out what went wrong. If it acts up again, you can follow the voltage from the battery to where the power is lost. You will probably need a load on the battery (such as the head lights) to see the loss.

GeoRoss

I agree that it was some place from the battery to the under hood relay/fuse box. While it was acting up I did check all the voltages. There may have been a few tenths drop on the 30A circuit. I don't think that was the cause as circuits on both the 30A and 40A fuses are affected. All fusible links/fuses ohm out fine. All wiring from the battery to the relay box and from the relay box to the F1 connector by the airbox had continuity. There was no ugly corrosion at any wire feed ends or terminals. They all looked ok. I cleaned all of them up anyway. I had checked and cleaned all grounds awhile ago, but the pulling and resetting of the 30A/40A fuses makes me think it was upstream of that. Somewhere from the feeds from the 80A fuse to the AM fuses or the fusible link to the the battery. I did not do any load testing nor expose any of the loom. It could be that main fusible link. I guess those need to be built now that they are NLA. I think it is a 3mm fusible length.

It works now. I'm just really confused by the symptoms. Low load circuits are fine, go to start (high load) and all those interior circuits go dead. Wiggle the AM fuses and the low load circuits come back, high load and all those low load circuits die. Later-Rinse-Repeat. Take everything apart, put it back together with some cleaning and everything is fine. Just a really weird symptom (acting like a breaker) and I was hoping to find a loose terminal or corrosion. I really thought I would find a loose terminal or wire feeding the fuse box. Everything was nice and tight, very little wiggle. If it comes back I'll do load testing on the circuits. I've got a bunch of different watt automotive bulbs and can use them to build different loads that I can apply to individual circuits so I can look for voltage drops. This little mystery will also justify the purchase of a Power Probe. I've wanted one for ages, just haven't needed one.

Thanks for the suggestions.

Co_94_PU

iTrader: (-1)

Suggested reading for you...

Voltage drop.. Particularly a loaded circuit voltage drop.