FJ80 Tranny / Shifting / electrical problem (1 Viewer)

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Denver, CO
First time posting, need some help!

97' LX450 starting "slipping gear" on a large uphill, coming off of a rocky pass out in Moab. Drove back to Denver no problem. The next morning I had the following symptoms:
- *only* when the engine/tranny warmed up, the truck would try start in 2nd or 3rd gear and lurch for about what felt like 3 revolutions of the drivetrain before scooting off no problem.
- Toyota/Lexus guys here said bad transmission (without even dropping the pan, of course)
- two tranny mechanics (one a 35yr GM guy, and legit) said tranny was doing exactly what it was supposed to do, and suggested valve body reman / new solenoid

So...
Valve body reman + new solenoid... great pressures internally, but same problem overall. Truck lurches between gears when going from dead stop to start, or, on a very steep hill where it drops a gear.

- Shifting from L-2-D and she shifts/runs beautifully. Driving it that way now with zero problems.
- transmission guy says that even when the rig is in manual L, he's reading his scope on the ECU telling the tranny the wrong/incorrect gear assignment (i have no idea what code or what this looks like)
- he states tranny is just fine and that it is an ECU problem (95% sure it's fried to be exact, his words)

Toyota / Lexus guys only state how rare it is for an ECU to be fried, and just continue to talk about redundant grounds in the engine compartment meaning it's almost impossible to have a poor connection... they're officially zero help at this point (Toy Car care in Centennial, CO, to be exact)

I've heard too many stories (and read on these forums) about bad earth/ground connections or dirty/loose electrical connections causing transmission nightmares. I read on a forum (Apr 3rd, 2012) about a transmission problem regarding the two wires running above the starter... I started there and cleaned those, but does anyone else have any ideas or know any other specific connections to check before sending this back in for another $450 diagnosis?

Thanks in advance!!
 
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Have you tried a different ECU yet? You could check the Parting Out section
of the Classifieds for a used ECU to test the theory.

 

baldilocks

Battle Ground, WA
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Are you not getting a diagnostic trouble code(s)? Seems like an ecu, or any other electrical issue in the trans circuitry would set off the check engine light. You could interrogate the ecu for old stored codes. You replaced how many solenoids? Have you adjusted the trans throttle cable (kickdown cable).

Too eliminate any possibility of this being a mechanical problem, disconnect the wire harness from the side of the trans and then drive it starting off in low and shifting up and down through the range manually. If this works out then your issue is definitely electrical.

Also, there should be aground strap from the rear of the transfer case up to the body, at least there is one on my 1993.

If the neutral safety switch or it’s circuit are faulty, your gear selector will send erroneous signals to the ecu about what gear you want.

If you don’t have a FSM, now would be a good time to get one.
 
Joined
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Messages
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Have you tried a different ECU yet? You could check the Parting Out section
of the Classifieds for a used ECU to test the theory.

I haven't. But I'll see if I can find something locally or check the forum. Thanks.
 
Joined
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Messages
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Location
Denver, CO
Are you not getting a diagnostic trouble code(s)? Seems like an ecu, or any other electrical issue in the trans circuitry would set off the check engine light. You could interrogate the ecu for old stored codes. You replaced how many solenoids? Have you adjusted the trans throttle cable (kickdown cable).

Too eliminate any possibility of this being a mechanical problem, disconnect the wire harness from the side of the trans and then drive it starting off in low and shifting up and down through the range manually. If this works out then your issue is definitely electrical.

Also, there should be aground strap from the rear of the transfer case up to the body, at least there is one on my 1993.

If the neutral safety switch or it’s circuit are faulty, your gear selector will send erroneous signals to the ecu about what gear you want.

If you don’t have a FSM, now would be a good time to get one.
I haven't received any trouble codes nor has the check engine light come on. I believe only #1 solenoid was replaced, I'll call the mechanic to confirm. The kickdown cable was just recently adjusted.

I'll try disconnecting the wire harness and see what happens... but for now, I'm driving from L-2-D just fine with no problems. I'll verify ground strap connection as well.

The mechanic did state that the ECU was sending erroneous signals about what gear it was supposed to be in, even while in manual low... which is why he pointed to the ECU. Wanted to verify/check connections before replacing it. I'll get on finding a replacement ASAP.
 

baldilocks

Battle Ground, WA
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Bad ecu’s happen about as often as you win the lottery but neutral safety switches and the associated wiring has been the culprit several times during my 6 years of reading Mud. Send an erroneous signal to the ecu and it will send incorrect signals to the transmission.
 

SUMMIT CRUISERS

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If you haven't done so yet, please inspect the Neutral Safety switch barrel connector. Located driver's side, back of the engine up high and is below the Pesky Heater hose as I recall. These things are about 9 out 10 times the problem with shifting due to corrosion that they develop from water/mud sling from the front tire.
 
Joined
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Bad ecu’s happen about as often as you win the lottery but neutral safety switches and the associated wiring has been the culprit several times during my 6 years of reading Mud. Send an erroneous signal to the ecu and it will send incorrect signals to the transmission.
Is this it?
If you haven't done so yet, please inspect the Neutral Safety switch barrel connector. Located driver's side, back of the engine up high and is below the Pesky Heater hose as I recall. These things are about 9 out 10 times the problem with shifting due to corrosion that they develop from water/mud sling from the front tire.
Is this it?

39ADF6F3-CC39-4F04-B18A-CFE5CF9243A9.jpeg
 

baldilocks

Battle Ground, WA
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He says the connector in question is located “up high”. It’s actually just below the pesky heater hose as he states (would not consider that up high) and just inboard and above the starter. It is the only round shaped connector in that clot of connectors.

If that connector is good to go then the neutral safety switch needs to be tested.
 

SUMMIT CRUISERS

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Here's another thread with a pic of it. I know it takes some long arms to reach it and work on it. That's why the up high comment but below the Pesky heater hose.

 

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