kcorpetti

Good day Forum!

I own 1993 4Runner with the 3.sl0w and 4spd Auto, and I have a problem very difficult to diagnose. My truck drives perfectly and smoothly, but when I gain speed and its time to shift into o/d, the transmission continues to upshift and downshift from 3rd to 4th at a very fast rate. Almost once per second. I had to switch the overdrive off to prevent any damage.

My mech (japanese toyota veteran) checked everything regarding the engine and ECU. Thermocoolant was bad. Replaced it along with new wires. Thermostat works. Problem still persists.

Also, the problem occurs at any throttle position. Even if I fully let go of the accelerator, the shifting occurs.

My transmission was rebuilt on February, but the problem started now. The tranny mech said that there's a thermo sensor in the tranny that only allows o/d to engage when temperature is adecuate. He says he cleaned it and the sensor looked and worked fine. He will check the tranny anyways, as it's still under warranty.

I've tried looking for similar problems on the web but havent found anything. If anyine has even the slightest idea, it will be greatly appreciated.

For this truck I have a Hayne's repair manual and, on its way, a OEM Toyota Repair Manual.

Thanks in advance!!

waskillywabbit

iTrader: (-1)

Please use relevant thread titles in the future.

Generic ones like "help" get deleted per posted forum decorum.

Thanks.

kcorpetti

I apologize. Thanks for correcting the title.

krytellan

Check engine light come on/get a code?

kcorpetti

Hey Krytellan. No, no CEL and no O/D light... at least yet.

UKMyers

Last vehichle I saw do that was a heep and it was being caused by a bad Throttle Position Sensor giving the tranny bogus info.

kcorpetti

I also believe that could be causing the problem, but would the ECU detect it and flash out a code for that? Also, the TPS was already adjusted during the rebuild (CEL gave code) because the transmission would start normal on Drive, but would immediatly upshift to 4th, no matter the speed. Is this problem possible even after the adjust? I mean, could it be that a missadjustment could cause it? It is, after all, only between 3rd and 4th gear.

Marc

Short out the diagnostic connector and check for a code.

thook

With some cases, just because a part is bad, you may not get a code. IOW, what the computer sees from the component in terms of voltage may not be out of the specified or acceptable range. But, the signal may still be erratic and/or not actually represetative of the true condition. For example, the TPS may be sending a voltage signal that tells the ECU the throttle is closed when it's really open.....or vice versa. This would be due to maybe worn areas along the circuit. In either case, the computer doesn't see that as abnormal because the voltage is still in acceptable range (hence, no code) and adjusts timing and fuel trim accordingly. However, since the throttle plate is actually open, you run into timing and air/fuel (or shifting with auto's) conflicts that create poor performance. Then, you may throw an O2 code because that sensor actually sees thing are off. Now, if the ECU lost connection intermittently or permanently with the TPS along any given internal circuit, you'd definitely throw a code.

Anyway, I believe Krytellan is suspicious of the speed sensor. So am I. If the TPS checks out fine, that's where I'd look next.

kcorpetti

Thanks a lot you guys.

Apparently, the problem has been "temporally fixed". Here's what I did:

Since the truck was held still for about 1 month, I decided to warm her up and check all fluids and sounds. While doing that, I played with the Throttle a little, meaning I made sure it was fully closed and then fully opened it in, and then closed again. I did this in a "fast" sense, in some way. I did it a couple of times, checked everything, and turned her off.

When I used her last night, I drove about 40 miles without a single transmission problem. I guess this only points out to the TPS. I'll ask the guy at the transmission shop to check and readjust it. I will let you guys know how it ends up.

thook

Ah.....good clue. Ask the guy to check the VTA circuit, in particular, for throttle plate movement. IOW, hook the meter to VTA and E2, watch the meter as you open/close the throttle, and see if there's any dropouts in resistance.

kcorpetti

Update on the Problem:

Apparently the moving-the-throttle temporal solution doesn't works quite as I hoped to, but I think its because the problem isn't there.

I believe that the throttle-thingie "helped" the problem because the transmission was cold. You see, I've noticed that the shifting doesn't occurs when the tranny is relatively cold, in my opinion. Also, I noticed that around 40mph, the rpms start to go up and doing. I'm 99% sure that this is the tranny's converter locking up and unlocking up. Now, what could cause the tranny to go from 3rd to 4th AND also lock and unlock the converter? I'm thinking it could be ATF thermo sensor. I dont think the TPS has any power over the locking of the converter. Anyone concurs?

thook

The torque converter won't lock up when the engine is cold, that's for sure. The coolant sensor is in part responsible for that. Don't know what how the ATF thermo sensor will affect things, though.

kcorpetti

My Toyota-veteran mechanic told me (he doesn't works trannys) to have my valve body checked and cleaned. He had a client with the same problem while tranny was hot and he had his valve body checked and cleaned, and problem solved. Everything outside the transmission has been checked and adjusted at least twice (coolant sensor, ECU, TPS and wires). It MUST be inside the tranny... i just don't know what. This has really been a pain in the lower back, because I can't drive over 40mph (or I start noticing the converter locking and unlocking up) nor can I use 4th gear.

Has any ever experienced this before?

betelnut

The overdrive is computer controlled and is engaged by an electrical solenoid, so you haven't checked everything.

At this site there's a lot of information about transmissions:
http://www.autoshop101.com/

Article AT11 has a simple check with a voltmeter to tell you what gear the computer thinks the transmission is in. That would tell you if the computer is sensing that the transmission is shifting back and forth.

Article AT24 has a whole bunch of stuff you can check, all things that may affect shifting. Pp. 22-25 have special info about O/D for our transmissions, and the rest of it has good diagnostic tests too.

kcorpetti

Thanks for the info. I'll look into that this weekend.

I do have a question. Is it possible for the problem to be caused by a bad solenoid? Maybe when the tranny's hot, pressure rises, and the solenoid no longer holds up as it is supposed to. What do you guys think?

hockeytown9

Hey guys, a quick note, I too am having this issue. A few years back we replaced the 3.slow in my wifes 4runner, with another 3.slow from Jasper. Was a nightamre as the shop we were using pulled the plug on us right after we started. This mean we only had a couple of days to do the job. So I enlisted some friends of friends to help. Only cost a few six packs, but the problem was we all had jobs. So we worked on the 4runner in shifts. So we would get there and just pick up where the other guy left off. We got the engine in, but had this same tranny issue pop up (among other issues). Wife has another car, but with winter approaching I need to get this baby running for me now (going to have to sell the 84 Toy p/u. boo hoo). So I will be looking in on this thread for tips advice if that is okay? Hope you don't mind kcorpetti. I think some wires were not connected correctly during the swap, which wires should I look for in regaurds to the tranny operation?

kcorpetti

Dont mind at all. If its the same problem, might as well post it in the same thread! One less thread to search for!

Regarding wires, i dont think thats the problem. The transmission worked perfectly for the first few months... which is why Im aiming at something that went bad instead of something that was installed/fixed incorrectly.

kcorpetti

*bumps*

madbomber08

We own a 1989 toyota camry with 200,000 hard miles and it has a similar issue as you are having with your 4runner. Driving at any speed, fast or slow, it will sometimes shift from o/d to 3rd iradically and vice versa. Sometimes we can be driving it with no troubles at all. It will shift and stay in o/d for the duration of the trip. Other times it is annoying and will stay in 3rd. The car has no RPM gauge so we feel as if we have to go 45 or less when it shifts down to 3rd because the ole girl sounds like shes revving way up there.

A few years back we replaced the ECU and ECM (if i remember correctly) because that is what the transmission tech. told us to do. It did nothing. We flushed the tranny, too. He couldn't figure it out after that and we really didn't want to spend any more money on an old unsafe beater. My cousin, who's a GM mechanic, thought it to be a shift solenoid. He doesn't want to mess with a *Toyota* though. She still runs great around town though, just not a highway driver.

Anyway, I just thought I would throw that out there. I know it's not the same vehicle and maybe even not the same problem. But I will keep following this and see if you figure it out because this is interesting.