I appreciate the help. 1st to 2nd is butter smooth without any weird behavior,
No worries.
Ok. I think that's how mine behaves although I have a 5-speed. The first two shifts are so transparent its impossible to tell there's an extra gear there.
Ok. THAT sounds like 'clutches' (bands) slipping. Increase in viscosity will definitely make a difference if that's the case. In the old days - and I think this still works the same - I'd suspect maybe the pump IF it did it in every gear. However, it doesn't so that's probably ruled out.
After thinking and reading my pin-out diagram, I wonder about the transmission fluid temp sensor. Maybe a long shot and I don't know that the TCU uses it to control shifting - although I'd be surprised to find they didn't - but maybe a possibility.
I don't believe you have a TCU. You have a PCM. In 2000 Mitsu went to an integrated ECU/TCU - called a PCM (Powertrain Control Module). AFAIKT, first release '99 3.5L Limiteds had a ECU and TCU, as well as all 2.4L and 3.0L. 2000 was the new 'model' and that's when everything changed for the 3.0L and 2.4L. The mid/late '99 3.5L Limited was more like a 2000 in design when it comes to electrical stuff. I don't think this changed in any of Mitsus sales areas.
Aside from that, I really don't think this is TCU related - as in there is something specifically wrong with the TCU (excluding something from a TSB). The only thing you MIGHT do is by shear chance get a TCU/PCM that was reloaded with the newer code - if I'm even correct about that in the first place.
Another thing, if you have a PCM, you also have the Immobilizer. You can't just change the PCM. The PCM and Immobilizer make up a matching set. If you replace either separately, you have to have everything reprogrammed or the vehicle won't start. You can't do this - it has to be done at the dealership.
... When the trans is still cold, and the engine temp gauge is in the middle (doesn't mean engine is fully warmed up), the trans shifts fine and has no delays in down shifting i.e. press the gas a little more and if rpm's are below say 2500 it'll smoothly downshift and go. However, when the engine and trans are fully warmed up, downshifting requires a significant amount more of the throttle depressed before it downshifts which at that point it downshifts aggressively because the rpm's try to spike before it engages into a lower gear.
Yep. Our dash gauges are weird that way.
I believe that is normal behavior. My '99 Limited did that as well as my '03 Limited. My '99 had your transmission and my '03 uses the Montero transmission - same behavior. The downshifting in my '03 is REALLY irritating, but both senior techs - who own and drive multiple Mitsu cars and SUVs - say that's 'normal'.
You are correct, its not mechanical or electrical. Shifting is controled by the TCU. However, when they integrated the ECU and TCU into the PCM, the TCU potentially has access to a LOT more data which can be used to control the transmission.
I have no way other than the FSMs to tell what is or is not used in determining transmission operation.
Take a look at pages 1-4 of the PDF I linked to. I documented the pin-outs for the 1997 ECM (ignore) and 1999 PCM. Nothing really changed between 1999 and 2005 for the 4-speed auto that I'm aware of. Yours should be exactly the same as what's documentated since the '99 Limited basically got the 2000 PCM before everyone else.
Piggy-back AEM F/IC 8 and Innovate LC-1 Wideband O2 Wiring Diagrams and Pin-Outs for 1997 Montero Sport 5-Speed ECM & 1999 Montero Sport Automatic (PDF)Montero Sport ECU/ECM and PCM Information1997 ECM
1998/1999 ECM
1999+ PCM
With a PCM, there looks to be the following ...
TPS, ECT, A/T fluid temp, Input and Output speed sensors. Possibly Cruise Control and 4wd and transfer low.
The problem is, were I programming the A/T, I could use half a dozen more inputs such as RPM, O2, IAT, and MAP and I don't know that Mitsu didn't. So, I can't tell you exactly what they do or don't use. I've talked to the senior techs about this quite a bit for years and they don't have much more visibility into it than I do and unfortunately don't have a decade of hardware programming and 30 years of IT background to give them insight.
If I had the TCU code I could tell you exactly what goes on, but I don't so ...
If you don't already have a set of FSMs (the real ones in print), I suggest getting on eBay and finding a set. You'll need a complete set because stuff is spread all over the place. 90% of a set won't help. There is a good section on troubleshooting that literately walks you through. Its the same as the techs would use.
Yep, I thought so. I would have them reprogram it irrespective of whether it was 'done' or not. I had them do my '03 just on principal to make absolutely sure it was done.
No. PCMs change between models and years. The chassis is the same for '00-'05. The internal hardware changed between '99 and '05 several times. The programming differs and changes in pin-out and sensors are what makes them not interchangeable.
This is what I do know for sure: ECM/PCMs are different between engine displacements, transmissions (both manual and A/T as well as between different A/Ts), newer vs. older design sensors, engine types (SOHC vs. DOHC), N/A vs. forced induction (turbo/supercharger), emission regulations (FED vs. CAL), and fuel type (gas/petrol vs. diesel) and any combination of the above.
Pull the kick panel and get the MD code and start surfing eBay and the salvage yards.
AGAIN, do not forget that you MUST have the matching Immobilizer. Not just the correct P/N, but the EXACT one that came with the PCM. Getting this off eBay or second hand seems to have about a 50/50 chance of success based on what I've read from the 3G/Dimomonte/EVO guys.
Also, having to get a matched set is going to up the price considerably. Into the several hundred dollar range.
Before doing this, I'd take it to the dealership and have them check everything out with a MUT and reprogram it. Then go from there. Replacing the ECM on a pre-'00 Montero or Montero Sport is easy and relatively cheap, but post-'99/00 ... it gets to be a real headache and expensive.
Edward