pplusent

93 4runner 3.0 auto trans 4x4. Alternator went out and had to drive about 20 mi on the battery. Since then the speedo keeps dropping to zero when it hits 3rd gear. I have changed the sensor with a spare and it works slightly better, but still drops out. It through a code once , but went back off. One time it dropped out and the transmission kicked itself into natural. Once down shifted into second it started working again. Is there a control module that may have been damaged by low voltage? If so, where is it located and what does it look like? If not, does anyone have any Ideas as to what is doing this.

scope103

The usual cause of "drop outs" like that is a weak (failing) sensor in the transfer case; your spare may be suspect. Or, the wiring from the sensor to the ECU. (I don't think this has anything to do with driving on the battery, but who knows?)

Someone on this site noted that the o-ring in the sensor had gone bad, admitting oil into the sensor (between the sensor body and the tiny spinning magnet). He cleaned that out (and replaced the o-ring) and reported success.

pplusent

I ordered a new sensor. It should be here Friday. The original had no o-ring at all and has been working for 12000 miles. The spare has a new o-ring. I had a similar problem before when it was eating sensor gears, but I fixed that by removing the spedo metal gear off the main shaft and removing the burrs left on the gear from manufacturing at Toyota. Now the gear slides smoothly and adjusts to the sensor gear. No more eating gears, The current sensor does have a missing tooth. What is odd is the way the transmission dropped into natural when driving as the speedo dropped out, that is what leads me to believe there might be a transmission control unit somewhere in the system. The wiring was inspected, it is old and there are some insulation breaks, but all seems to be intact and not broken or burned. We will see what the new sensor does.

Co_94_PU

iTrader: (-1)

Fix your compromised wires, before it does really bad things you know like burst into flames...

Given all your other transmission threads, one in particular where you replaced the solenoids, how is it you don't know where the ECT computer is still, you sir need a service manual or to read the one you have.

pplusent

I have rebuilt most of this vehicle, but the only modules I have come across is the ECM by the evaporator and the cruise control in the drivers side kick panel. There is no modules under or behind the radio or in the engine compartment other than the spark control unit, so no I haven't come across it. Manuals I have are short on this info. and my best manual is the Toyota one but it is for 88 to 90 4runners. Great manual for the transmission but that's about it. the wiring is not the same.. I haven't been able to find a TCM at any of the parts stores, so I am thinking it is part of the ECM. I also have used the best of three wire harnesses and it's not that bad to start a fire. the biggest problems with wiring is at the plugs and have been repaired for the most part. This vehicle came to me in boxes, I had to figure out where everything went on the vehicle. I do not believe it is bad wiring although I may replace the VSS that reads off the main shaft, It has a small Knick on one wire(not the speedo sensor, I am already replacing that unit and its wire is unbroken). As far as the solenoids, I have rebuilt this entire transmission from two downers and the original that the previous owner cracked in half trying to force it over a pre mounted converter. The problem then was a defective new converter, it would not lock up and being it was new I had to check every possibility first.. For now I have to find the problem before the end of the month when I'm going to be driving into Mexico. Other than the speedo it runs like a champ other than the lack of power in the 3.0 and give it another 50000 miles or so and I am changing the drive train to a 4.3 Chevy for power and reliability. For now I have to make the 3.0 do the job. Love the size, utility and ride of the 4runner and will keep the body. So if there is a TCM please let me know where its located, can't find it in the manuals, or online schematics , or diagrams. Not a lot of info on the 93's, and lots on the 2000 and above.

pplusent

Are you saying it is controlled by the ECM/ ECT main computer? I believe ECT refers to a engine coolant temperature sensor, or an electronic controlled transmission.

Co_94_PU

iTrader: (-1)

The 88 manual you said you have, it says "remove the shifter cover, disconnect the ECT ECU" right? Now if it's not there and you haven't seen it elsewhere it's safe to assume it's part of the TCCS ECU, no?

Anyways, yes it's built into the main computer.

ya still need a manual and to fix any exposed wire.. until that wire is replaced you can't be certain it's not the cause, if it's brittle in one spot it's likely brittle and damaged elsewhere, like on top of the transmission where everyone tends to report short circuiting to the case..

Ps, having your transmission drop to neutral is by no means safe and cars burn up faster than you can blink from way smaller things than exposed wires..

pplusent

The tranny dropping into natural is by far my biggest concern. the wire looks like someone probed it with an ohm meter. At the time of the trans rebuild all the wire was inspected and new wrap was installed, so I am sure the majority of it is good. It isn't making sense that the tranny would drop out just due to the speedo sensor being bad. The actual VSS would make more sen
se because that feeds the computer with the shaft speed in the transmission. Hard to believe that would go out though being it just picks up a magnetic pulse, but I will test and replace if needed. I am starting to believe from the symptoms that the control unit may have been damaged by low voltage. I will dig into it tomorrow and see what I come up with.

pplusent

Finally got all my parts. Put in a new odometer sensor because the old one was missing half a tooth. Since both Vss sensors were throwing a code and the transmission solenoid was kicking out in 4th gear i figured there were to many issues all at once to be any one sensor, or wiring. I found a used computer on eBay for 30 buck and installed it. I have only tested for a few miles, but the odometer is working, the vss is not throwing a code and the tranny is staying in gear. It also is idling smoother and a small miss at idle i have been chasing is gone.I believe the ECU had an issue and when voltage dropped running on the battery the computer just went out.
I also installed a a ford Taurus fan and controller ( gained what feels like 15 HP) and a new a/c compressor, TXV valve for a 95 (134a) and receiver dryer. All is working great, but not happy with fan clearance. Clearance with the fan motor and pulley is only 3/32 of an inc, we will see if issues come up on that. Now if I can get the cruise control working everything will be working, finally, it's been a long road!