townending

Hello everyone, I picked up a 1992 4runner (3VZE - M/T - 4x4 - SR5 - 200K miles) and have one issue that I am having trouble tracing. I am hoping someone is gonna step in and tell me it's a simple fix that I've been overlooking. Please keep in mind, this is by far the oldest car I have owned.

My issue? The car will shutdown randomly while driving. I say randomly because it can happen at any load, any rpm, any speed, no warnings. When the car dies, there is no sputter/hesitation, it just dies. I can restart it and continue to drive for a short amount of time before it dies again, each time I restart it it dies faster than the last until it's shutting down every 5-10 seconds. IF i swap the EFI relay, I am immediately good to drive until the new one burns(normally 150-300 miles). It seems that 1 long drive will kill the relays faster than numerous short drives. My guess it the longer drives allow it to build up tons of heat. Please check the below pictures

Here the parts I've replaced in an attempt to fix the issue, as well as just do some maintenance on the car
-NGK Sparkplugs
-Sparkplug Wires
-Distributor Cap and Rotor
-Fuel Filter
-Replaced Air meter / flapper
-Replaced EFI Relay (New ones get burnt after about 500 miles)
-Replaced EFI Circuit Opening Relay
-Oil Change (Amsoil 10W-30)
-Valve Cover gaskets
-Upper intake manifold gasket
-Radiator
-Upper and Lower Radiator Hoses
-Coolant Bypass Hoses

What I plan to replace next:
-All Vacuum hoses (I gave the engine bay a very light quick rinse while it was running causing the engine to bog down)
-O2 Sesnor
-Speed Sensor (I replaced my speedo, but speedo still doesn't work. The speedo not working does not bother me, but the speed sensor is tied to the EFI ECU)
-Throttle Position Sensor (I will test / realign before replacing)
-ECU

Any help is greatly appreciated, thanks ahead of time.

Here is the EFI relay (Left) that was in the car when I bought it next to a junkyard EFI relay (Right)


Here is one of my many burnt/starting to burn relays after only 150 miles.

ksti

I have heard that the o2 sensor wire can catch on the exhaust burning it up causing this problem.
Trace that first before you throw anymore parts at it.

scope103

I can't tell from your pictures, but I think your burned tab is pin 5 (it will say on the top of the relay). That should be the pin attached to the EFI fuse (12v).

Since you're burning at one tab (not both, and not inside the relay), my best guess is that you have a loose relay socket. As the relay jiggles while driving, it is quickly making and breaking the connection and building up a lot of heat. This could be in the socket itself, or it could be where the wire is crimped to the socket. If it's the former you might be able to get by for a while by "repairing" the socket with pliers to make it grip tighter. If it's the latter, that won't help (and might make it worse).

You could try rigging up a test LED (an incandescent test light probably wouldn't be fast enough) to a 1/4" spade connector. Connect the other end of the test light to ground, and with key-on the light should light. Tap the side of the junction box; if the light flickers you've found your problem.

RAD4Runner

+1 ^^^^
Toyota parts are almost bullet-proof. The problems usually lie on the way they are put together (like above) or maintained.

May of the above parts have no relation to your problem. Focus on your most important/critical problem first, then worry about the rest later.

townending

While the wire itself looks to be in good condition, for whatever reason the wire is wrapped around the torsion bar.... The O2 sensor is cheap enough that I will replace it anyways. Thanks


You are correct, it is pin 5. I'll double check the where the wires crimp to the EFI relay socket. For what it's worth, the EFI relay is in the socket snugly, its a royal PITA to pull the relay out, but now I'm wondering if the pin in the socket is burnt as well.

I'll attempt to rig up an LED to test. Thanks

That's what I've heard. While I had the valve covers off I was pleased to see no sludge / buildup what so ever. However, there is alot of odd "cheap fixes" I'm finding as I work on the car that don't sit too well with me.

All the parts I listed under plan to switch, with possibly exception of the vacuum hoses are directly tied to the EFI system. Relays most commonly fail due to overcurrent or the relay "swtching" too often. While the above post recommending I check the socket / wiring for loose connections is a great start, I am not ruling out over-voltage / erratic signal triggering the EFI relay too often possibly due to a faulty sensor somewhere in the EFI system. Thanks

scope103

Good news! You CAN rule all that out.

There are no sensors that drive the EFI relay. You turn the key, 12v is applied to the IGN fuse which goes to the EFI coil to ground. The relay closes (pin 5 to 3), which connects the always-on EFI fuse to power the rest of the EFI system (ECU, COR, VSVs, ...)

You can have loose wires and bad connections anywhere, but there are no sensors in the circuit that closes the EFI relay. The only source of voltage is the battery and alternator; if your alternator is putting out over-voltage you'll have plenty of things go wrong before it affects relays. (But checking the voltage at the battery with the engine running is so easy and useful, I'm not going to discourage you from doing that simple check.)

RAD4Runner

Yep.
With engine idling, voltage at battery post should be from 13.5 to 15.1Volts.

townending

I've never dealt with an early EFI system, so this is great information to have.


I did some looking around the engine bay and found this under some tape.

Looks like the black wire and the black / white stripe wire are damaged.

townending

I repaired one of the wires above. However, the black wire is a shielded wire which only had the shielding damaged so I left that for now. I was curious as to what needs a shielded wire down underneath the car. While I was tracing the cable, I noticed an electrical connector that is completely smashed/broken. It leads to what I believe is a sensor that is on top of the transfer case. This should not be confused with the speed sensor. Anyone have any ideas what this is? Is it important?

On a side note, car was in limp mode for my first drive (20 miles) after repairing the wire, but has been fine the 4 days since (About 350 miles). I do plan to replace the harness once a local junkyard gets a manual 4x4 in.