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MGF Steptronic Gearbox Problem or that it seems

10K views 7 replies 5 participants last post by  ALPHABAR 
#1 ·
Hi I have an MGF year 2000 1.8 Steptronic, had the car in Venezuela for a long time now with no luck at all in getting it going.

So far changed many sensors with no luck what so ever, the car seems stuck in 3rd gear, it can get up to 50 mph on 3rd gear or that it seems, have changed the output shaft sensor, speed sensor, gearbox ecu and still no joy.

Shaf very kindly send me some info on checking for electric faults ,, they all seem to be fine, all the electrics I mean....

Have spoken to several garages whom tells me that it has to be the gear box, I would like a debate on this if possible with as much as positive information.

Have even spoken to an especialist who states the same, but some other mechanics assure me that it has to be an electrical fault.

kind Regards
 
#6 ·
Hi Alphabar,

I thought you had sorted it out because I didn't hear from you for a while.

I think you need to explain all the syptoms again.

How does it feel when you accelerate from rest.
What engien speed does it give.
Are htere any warning lights on.
What happens if you use the manual shifting.

I remember it really sounded electronic before.

The basics of how the box works.
There is a belt between two sets of cones. At rest or with no clamping pressure the belt will be in lowest ratio. It will always start from this ratio, it physically cannot start from any other ratio due to the way the pressures work.

There is a small valve in the gearbox called a compensating valve. On one side is a hydraulic pressure proportional to engine rpm, on the other is a spring pressed by a stepper motor.

If the pressure on the first side of the valve is higher than the force on the other side the valve will move. So if the engien speed rises, the valve moves and allows oil to flow to change the ratio. If you want the engien speed to rise (in manual mode) then you have to actually move the stepper to change the force on the spring balancing out the change of the hydraulic signal.

So for it to be Stuck in 3rd gear, the ECU would actually have to control the stepper motor. This is not one of the limp home strategies.

More likely the stepper motor has moved to a certain position and is fixed there. I think this is a limp home strategy.

If this is the case then the car will start from rest normally but once the engien speed reaches a certain point it will hold that speed no matter what.

Shaf
 
#8 · (Edited)
Hi Alphabar,

I thought you had sorted it out because I didn't hear from you for a while. not found a good mecanic down here

I think you need to explain all the syptoms again.

How does it feel when you accelerate from rest. SLUGGISH
What engien speed does it give. CAN REACH 55MPH
Are htere any warning lights on. AFTER 2 MILES THE YELLOW TRANSMISSION LIGHT COMES ON AND CARS TEMPERATURE GOES UP
What happens if you use the manual shifting. DO NOT WORK AT ALL[/B

IN REPONSE TO YOU SHAF ,, CHEERS ONCE AGAIN
 
#7 ·
HI SHAF
THANKS EVER SO MUCH FOR YOUR RESPONSE,,, FINALLY I FOUND A MECHANICAL ENGINEER AND WE SAT FOR HOURS TRANSLATING ALL YOUR EMAILS ... YOU HAVE BEEN VERY KIND INDEED ,, I WROTE THIS ON A NEW THREAD ,, BUT WOULD LIKE TO PLACE IT HERE FOR YOUR OPINION,,, AND THANKS EVER SO MUCH FOR EVERYONES REPLY TO MY THREAT:

Hi ,, My Mgf Steptronic Year 2000, Has Gone Into Limp Home Mode And Iam In Venezuela (south America) ,, I Took It Our With An Engineer (mechanical) Bmw And He Is Reuqesting A Giagnostic Troubleshoot For The Following:

The Car Can Be Driven It Seems To Be On 3rd Gear It Picks Up Speed It Gets To About 50 Mph And Can Do More, But Iam On A City, When Changed Onto Sport Mode Neither The Gear Atick Nor The Wheel Controls Change The Cars Gear.

About 2 Miles And The Cars Tempature Starts Going Up And The Yellow Light On The Panel Comes On.

I Am Waiting For A New Giu Gear Interface Unit ---

And We Will Be Ion The Process Of Checking All The Wires As Per Shaf ,, Whom Very Kindly Gave Me Some Information A While Ago.

Any Ideas On The Troubleshoot Guide, Book Or Cd

It Has Not Been Easy To Find A Reliable Mecanic Here ---

Any Suggestion Will Be Apreciated.

Max

PS WHEN I SAY 3RD GEAR THAT IS WHAT IT SEEMS..
 
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