Automatic Transmission Failing When Hot

[Tadao]

I have a '93 Pajero and this August the transmission started acting up. It happened just as I almost ran out of diesel so I thought it was related but now I think it was a coincidence. I got the fuel filter replaced and lines blown out in case there was any gunk but it didn't help.

The transmission had begun shifting early and then once the engine was hot it would not shift into first. Now every time I come to a stop (when the engine is hot) it wants to start in 2nd so I have to manually shift down to L to get going and then back to Drive. Today, a new problem happened: for the first time I couldn't get into my overdrive gear on the highway and was stuck at 80 km/h at 3000 rpm. After about 5 minutes the last gear finally kicked in and I could get to 110 km/h at about 2800 rpms.

I took it in to one of the popular local RHD shops and they changed the transmission fluid, replaced the filter, checked temp sensor, adjusted TPS (don't know what that is) and the kick down cable. Replaced a 2 pin sensor. They said it wasn't fixed and hoped an additive fluid would help. They weren't sure what to do next so told me to monitor it. It still isn't working and I need some advice/ideas about what could be wrong with it. (I've spent a lot of money already but think I should take it back to the shop.)

Thank you for any ideas you may have,
Mark

[Big-Bird]

TPS: Throttle Position Sensor. Tells the engine where your accelerator pedal position is. If the TPS is in the wrong position the tranny won't shift at the right time or at all.

The tranny has a few different sensors and a computer....albeit a simple one.

Your transmission could have genuine mechanical problems like a faulty front pump or the clutch packs are worn out...and yes auto tranny's have clutch packs.

There's a tranny sectionfor Pajeros in the UK Mitsu website but its possible the Delica Manuals would be of help. Look in the tech section of this forum.

[Tadao]

Thank you, Big-bird. Very helpful. Would you suspect that since the problem occurs once the engine is hot that it is more likely to be a sensor than electronics, the cable or the TPS? Could the clutch pack or pump work when cold but fail under high temps?

Thanks again,
Mark

[Big-Bird]

Tranny's can misbehave for various reasons....the more likely source of your problem is electrical. He Delica trannys have a many sensors/switches that have been know to fail. There are 5 of them just for detecting park, neutral and the 4WD Lever positions. These animals are mounted on the top of the tranny....real pain to get at. It may not be a sensor perse'......it could be a faulty wire going to a sensor.

Mitsu eletronics are tricky and I have fixed more a few gremlins in my L400. When my abs light illuminated its not because the abs was faulty....its because one of the 4wd indicator switches has failed....it lights in 2wd and goes out in 4wd....how the hell is the abs even remotely connected????(some real WTF stuff).

There are other weird ones that show up when the batteries are weak or the alternator has failed.

Probe the UK mitsu website...these guys show lots of troubleshooting tips with diagrams and such.

[Big-Bird]

I am checking with a good friend of mine who is a Pajero wizard...in fact he is the main admin of '4x4wire.com' where lots of Pajero and Montero owners tend to hang out. You could try trolling over there as well or at least search their database for a hint of what the issue might be.

EDIT: Here's what he provided.

First thing I'd check is the hold button. Where it sits in the console, it's easy to spill coffee etc down there. If hold button is deployed, it would likely manifest itself the way described. At least disassemble switch and shoot it with contact cleaner etc. Costs nothing. After that I'd be checking temperature sensors as there is more than one.

[FalcoColumbarius]

Not sure how I missed this one when it was first posted, I've moved it to the Pajero forum.

Falco.

[Tadao]

Took it back to shop, had another sensor (2 pins) replaced but it didn't help. Had AT filter and fluid changed. They couldn't figure it out. After a month or so driving like that, it began to drop out of OD after about 10 minutes highway driving. I could only reach 100 km/h at about 3000 rpm when usually it would run 2500. Today the AT light came on and stayed steady about 10 minutes into the trip. Checked AT fluid and it seems to be full but clear pink (not cherry red). didn't notice a smell.

Any ideas?

Thank you!

Mark

[Big-Bird]

Did you clean up the OD switch in your center console?

If so my position is your tranny has an emerging mechanical issue.

[PHIL]

Did you clean up the OD switch in your center console?

If so my position is your tranny has an emerging mechanical issue.

I believe BigBird has overstated my knowledge base on Pajeros...LOL. Be that as it may, I have some additional info I can provide. Given that you didn't follow up since February, you may or may not still be needing answers, but chances are somebody else may be having similar probs so...

With my Captain Obvious hat now on...

Electrical problems are certainly a possible, based on the info you gave us, but if we could take a step back first...

I'd be curious about the condition of the fluid when it was first changed. Burnt smell and lack of red color is indicative of bad fluid. These trannies are bulletproof if the basic maintenance is looked after: fluid change with the right fluid. Mitsu trans are very specific to their juice, and I've know more than one paj/Montero that had failure due to the wrong fluid. This is not only specific to Pajeros, of course but I think it's worth mentioning because they seem to be sensitive to the wrong and/or deteriorated fluid, and are otherwise very very durable

The other enemy is heat. The trans cooler runs to the trans via the bottom of the rad, so an engine that continually runs hot is dumping some of that heat into the trans. Old fluid doesn't have the same heat carrying properties. An obstructed or internally blocked cooler is another possible problem.

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