G'day all,

Just bought a '91 4-cylinder TR Magna SE sedan second-hand, about 140,000km on the clock. Car was in good nick, however since purchasing it about a month ago have had one engine mount replaced (cracked). Also had the 140,000km service done, and all of the hoses and belts replaced.

Since having the engine mount replaced, the car has a strange problem with the auto transmission. After driving around both city streets/highway for a while (80km or so) in D, and cruising along at constant speed, the auto drops several gears, and then after a while finds the right gear again. As you can imagine this can be a bit scary when you are going at 100km/h on the freeway in 4th and then the auto drops into 2nd... the car shudders pretty violently and revs go up quite a bit (to about 4500rpm or so)

The problem is a bit sporadic... it will happen a couple of times in succession, then not happen again until you are 20 k's further down the highway. Mentioned this at the service, they found that the TPS terminals were corroded and the connector boot was split, however these were cleaned/replaced and showed no probs.

Took the Magna out for a drive again today, problem still there as worse as ever. Will be driving this car from Brisbane to Sydney in a few months, so I really need to get the problem fixed but am at my wit's end trying to figure out what could be causing the problem.

Have any other 2nd gen owners had similar problems before? I am thinking that the TCU might be faulty (not sure though, this is my first Magna :D ) Any ideas would be great

well i'd put it down to:

*A faulty TPS that needs replacing instead of just cleaning up the terminals
*faulty pulse generator
*electrical fault with a sensor (cut/loose wire?)

i once had a spare TCU from an EFI magna, and put it on my carby magna... and it produced behaviour like this... which is why it makes me think one of the sensors is not giving a correct reading to the TCU. (the efi TCU is deisgned to read in the TPS reading from a EFI throttle body, not a carby TPS)... it's the TCU that ultimately controls the transmission and gear shifts...

it may very well be a faulty TCU as well... something internal to the TCU - leaking capacitor, etc etc... TR magnas are coming up for 15-16 years old...

is it related to how hot the motor is running? ie, still does it before the temperature gauge gets to it's normal operating temperature?

Since having the engine mount replaced, the car has a strange problem with the auto transmission. After driving around both city streets/highway for a while (80km or so) in D, and cruising along at constant speed, the auto drops several gears, and then after a while finds the right gear again. As you can imagine this can be a bit scary when you are going at 100km/h on the freeway in 4th and then the auto drops into 2nd... the car shudders pretty violently and revs go up quite a bit (to about 4500rpm or so)


My previous mechanical experiences all point to the convertor or bands slipping.

The problem is that the longer it happens for the more frequently it will happen and get worse each time.

Is it possible that the wrong tranny fluid was used??

NEVER EVER use DEXTRON in a mitsu tranny built after 1990.

Sounds like one of the shift control solenoids on the transmission valve body sending an incorrect signal.

TG

is it related to how hot the motor is running? ie, still does it before the temperature gauge gets to it's normal operating temperature?

The problem only ever occurs when the engine is at normal operating temperature, and always after the car has been driven for about an hour. If it is a sensor problem, perhaps the sensor is degrading when it is hot. Since the problem only occurred after the engine mount was replaced, would it be possible that this damaged a sensor?

Not sure about bands slipping, the problem can occur when the auto is in different gears, not just 4th. Though then again, seems to get worse each time I have driven it. Last time it happened, I was driving at various speeds up to 70km/h, and the car was stuck in 2nd. Thought this might have been the "fail-safe" feature activating, however the car miraculously returned to normal after slowing to about 15km/h and then accelerating again.

Going to book the car into a Mitsu dealer to see if they can identify the cause this week, will keep you posted :)

Problem solved! Cause was a faulty TPS, had been repaired in the past and had broke :( Also got a sonic injector clean and a replacement fuel filter to do something about my atrocious fuel consumption (400km/tank in the city)...

Cost: Not cheap :rant: ($600 for the new TPS, $300 for the sonic clean + fuel filter) at my local Mitsubishi dealer in Wynnum, Brisbane

Ah well, my Magna is happy once again!

Problem solved! Cause was a faulty TPS i had a feeling it was... my automatic in my car has been through everyhting, and from what you described, it sounded exactly like when i was fiddling around with my TPS trying to get my auto to kickdown - it just stopped doing it one day. I ended up getting a new TPS, but it was $40 from a wreckers.