1990 3.0 LS V6 Auto 200k

My mechanic can't tell me why it won't shift into overdrive unless I've heated it up quite a bit. He suggested taking it to a transmission place, which I did. They said that they'd have to open it up to see if it was the trouble, which costs about the same as rebuilding it.

Once it does shift into overdrive, it drives fine, shifts fine, until I stop long enough for it to cool off.

So it doesn't make sense to spend $3000 to rebuild a transmission that may or may not be the problem.

Which means I might have to sell it - as much as I hate to. I wonder if I'll get more than $1000 for it?

If anyone has any suggestions, please let me know.

Thanks,

Ken

I thought you had it working when you replaced the thermo switch. Did you replace it with a new one, or one from a junker?

Since the switch reads water temperature, try replacing the thermostat with a new one from the dealership. It's possible that the thermostat is sticking "open" and taking too long for the engine to come up to operation temperature sufficient to trigger the switch (176 degrees, if memory serves me correctly).

If that doesn't do it, I'd check the electrical connections on the O/D "on/off" switch, the wire from the temperature switch, the O/D OFF relay and the O/D OFF solenoid. I'd also check the O/D "on/off" switch for resistance to make certain the switch isn't degraded and can't pass the signal. The ignition switch should also be checked to make certain it has no internal resistance and the connections are clean and tight with no corrosion on the wires.

If you can find a spare ECU, it would be worth a temporary swap to see if the problem goes away, but I don't think that's the problem. It's more likely to be a bad sensor/switch/relay/connection.

I wouldn't give up and rebuild a transmission until all of the above has been done.

Good luck,
Frank

Where do you live? Is it really cold there right now? Your transmission isn't supposed to shift into overdrive until the engine is warmed up. There's a special sensor on the front of your thermostat block especially for that purpose. I think it's the one on the front of the block furthest to the right if you're standing in front of the engine; it has a single wire attached to it. Anyways, that's the sensor that, once warmed up, allows the automatic transmission to hop into 4th. If it seems irregular to you, clean off the lead with a scratch pad and reattach the wire. If that fails to please you, buy a new sensor and screw it in.

I think this is it:
P/N MD102329 - Switch unit, water temperature
and retails for about $50. Kinda pricy, but far less than rebuilding your transmission.

You can also remove the switch and test the resistance at cold and and operating temp to see if it has gone bad. I'm sure Frank will follow up with the correct proceedure and numbers. <img src="/forums/images/graemlins/wink.gif" alt="" />

Oh, and btw - for $3000 you can buy a new transmission from Mitsubishi. You can get a rebuilt unit at Autozone for just over $1100 with a $450 return core charge... if I understand correctly, that's just over $650 for an essentially new transmission with a one-year warranty if you can do the installation yourself!

Thanks Frank. At one point, I thought I had it licked, but the next day it was back to the old tricks. I didn't replace the sensor with a new one, but I did test it before installing it, and it was working properly.

But even if I bypass the sensor and ground the wire leading to it to the engine block (which is what happens when the switch turns on), it still doesn't shift.

I've got the Chilton's again. I'll work on it today.

Well, that doesn't mean that the switch is good, but it probably is. What it means is that there's a problem further down the line. Forget the switch for now, keep the ground wire on the switch and work through the rest of the list I gave you. Keep at it - you'll find it.

Frank

This may be completely off base- but is your kickdown cable sticky? I had to lube it and work it 'till it moved freely, and then all was good...just a thought, as I am not a great mechanic.... <img src="/forums/images/graemlins/notooth.gif" alt="" />

I'll try anything. What's the kickdown cable, and where do I find it?

It is on the opposite side of the throttle cam, Has an orange rubber "boot" on it...pull the boot back and drip tranny fluid on the cable, work it back and forth to help it move down the sheath, until it moves freely.

note: I used lithium spray grease, and was scolded by the real mechanics on the board- they said it is incompatible with ATF.... <img src="/forums/images/graemlins/shocked.gif" alt="" />

If you have removed your cruise control box, or if you suspect it may be bad, your O/D will not work. Basically, your O/D trigger wire runs through your cruise control box, the one behind the passenger side kick panel. With that removed, or malfunctioning you will not have O/D. You can jump between the terminals and gain back your O/D. Let me know if you want to try it and I'll take a pic for you.

I'd think if it were a "sticky" kickdown cable that it would be felt in lower gears and not exclusive to 4th. It might still be the kickdown cable - just not adjusted properly. You can adjust the point that it shifts by adjusting the two nuts that clamp it onto the bracket behind the throttle.