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  #1  
Old 08-09-2006, 12:20 AM
subru92svx subru92svx is offline
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Question AWD problem

I have a 1992 LS-L and while working on my car I had it on a lift. I started the car while in the air, but only the 2 front tires were moving. Is this how it is suppose to be? A bunch of other students at school were tryin to tell me my car was messed up. I called the Subaru dealer near me and explained. They said it was normal, but I don't know. The car does not make any strange noises or anything. The only thing I could think of was about 30,000 miles ago I had a shop fix my differential after I chipped teeth off my ring and pinion. I thought if something was wrong maybe they messed something up while they were working on it. Do all four wheels spin when your SVX's are in the air and running? Would appreciate any feedback. Thanks
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  #2  
Old 08-09-2006, 01:40 AM
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yes 4 wheels should be spinning for an awd SVX when it's lifted up in the air...

that means your awd is not working. maybe your transfer clutch is gone or something is not right on drivetrain......is your "green power light" blinking after you start up your SVX?
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  #3  
Old 08-09-2006, 02:32 AM
subru92svx subru92svx is offline
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Yeah my "green power light" blinks when I start my car, but goes out after a few seconds along with all the other lights. Is there someway I can pinpoint what is wrong?
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Old 08-09-2006, 10:39 AM
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Does the power light also blink when the wheels are on the ground?

If so check the error code generated by the TCU using the instructions found on http://svx-iw.com in the SVXipedia.

This is just another reminder for me to scan the FSM on the list of inputs the TCU uses to determine when to transfer power to the rear wheels.

My dad found out that if you unplug the TPS all 4 wheels will spin in the air. The TCU, when seeing 0% throttle, sees no need to send power to the rear wheels.
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Old 08-09-2006, 05:47 PM
redsvx94 redsvx94 is offline
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Yes, This is also what I found when i took my car in a transmission shop. The rear wheel won't spin under idling but it will spin as soon as one steps on the throttle.
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Old 08-09-2006, 06:02 PM
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Quote:
Originally Posted by redsvx94
Yes, This is also what I found when i took my car in a transmission shop. The rear wheel won't spin under idling but it will spin as soon as one steps on the throttle.
Try it on a slippery surface, like wet grass or gravel, get some one to watch from the side to see if the front wheels spin only, or all spin.

Harvey.
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  #7  
Old 08-10-2006, 08:03 PM
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Your AWD clutches are tired. What happens is that the wheels spin when you give it gas because the line pressure in the trnsmission goes up. This applies more force to the clutchpack. Eventually the clutch pack will not work anymore. It can also be a problem with the duty c solenoid, or maybe other solenoids in the tranny. you need to read the blinking light to see what it is telling you. The tranny codes are pretty clear cut. The other thing that will keep the awd from operating is a failed speed sensor.


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  #8  
Old 08-13-2006, 10:51 AM
subru92svx subru92svx is offline
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I found out how then read the blinking power light to get the TCU codes. It was code 11 which is duty solenoid A on the list of TCU trouble codes. I have also read though that the most common trouble code is 11 and it is almost always caused by a faulty transmission resistor located between battery and fender. How can i check to see if it is just the resistor? Also what does the resistor do?
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Old 08-13-2006, 06:13 PM
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Quote:
Originally Posted by subru92svx
I found out how then read the blinking power light to get the TCU codes. It was code 11 which is duty solenoid A on the list of TCU trouble codes. I have also read though that the most common trouble code is 11 and it is almost always caused by a faulty transmission resistor located between battery and fender. How can i check to see if it is just the resistor? Also what does the resistor do?

DUTY SOLENOID VALVE "A".

This is a pulse width modulated duty solenoid valve, ( Sometimes known as a pulsoid). The device is incorporated in the SVX transmission control system in order to adjust line pressure in the following manner :-

The fluid line is provided with a bleed or bypass via an on/off device, in the form of an electrically operated valve. This solenoid valve is opened and closed repeatedly, in a rhythmical manner by a control current which is turned on and off by the transmission control unit (TCU) at a very fast rate. The valve is a normally closed device, and remains closed in the event of the loss off a control current.

After passing through this modulated solenoid valve, the continually interrupted pressure is in the form of a pulsed flow. When the peaks level off with the troughs, there is a resulting overall steady reduced pressure. The level of this pressure is adjusted by varying the on/off intervals. Most often the length of the on time is adjusted and the number of on/off pulses per second is kept constant. The usual rate is around 50 cycles per second.

The resulting adjusted output pressure is therefore delivered as a rapidly fluctuating stream. The system incorporates an expansion chamber as a smoothing element, which works as a sort of cushion. This device is usually in the form of a cylinder and piston or diaphragm, backed by a coil spring. In the SVX system the component is described as a Pressure Modifier Accumulator. The high pressure peaks in the stream press the piston outwards and become rounded off, while the low pressure troughs are filled in as a result of the piston moving inwards under spring pressure. The end result is a smoother level of pressure, such that controlled devices are not materially affected.

An increase in the volume of fluid controlled, is achieved by transferring the solenoid regulated pressure, to a pressure modifier valve and a regulator valve.

It should be clear that by “chopping” the fluid supply in an adjustable way, pressure control is achieved economically using a simple poppet type solenoid valve, with few mechanical or electrical complications. However the valve remains in a continuos cycling mode, which imposes rather arduous mechanical stresses.

THE DROPPING RESISTOR CIRCUIT.

It will be immediately apparent that a sudden on off cycle tends to cause what could be called a hammering of the valve seat, even though this is largely checked by the viscosity of controlled fluid flow. The dropping resistor introduces a second series of current pulses applied in parallel with the control signal. These shorter pulses are applied during the off cycles and timed to check the travel of the armature as it reaches the closed position, thus reducing both shock and noise. These secondary parallel signals in effect, “round off” the closing period and reduce the closing shock. This arrangement can be made even more sophisticated and configured so as to soften the the opening cycle, as well as the closing of the valve.

It will be appreciated that reducing the resistance in the circuit, or opening the circuit by omitting the dropping resistor, has two outcomes. Firstly the relative electrical off time is increased thus increasing the line pressure and therefore makes shifts more abrupt. Importantly as a second issue, increased shock loads are applied to the valve.

It is a documented fact that the line pressure control solenoid is the first to fail due to having by far the most arduous duty to fulfill. Failure is usually mechanical resulting in the valve seat not closing properly and as a result line pressure is markedly reduced. The end results are drastic, especially in respect of transmission friction surfaces. The fault will not necessarily be registered as a fault code, as the armature of the valve can be in the fully closed position with the problem confined to a worn and faulty valve seat. In the event of an electrical fault, which will register, the valve being normally closed, will fail safe and result in maximum line pressure.

The resistor should measure between 9 and 15 ohms to be within specifications. The usual is about 12 ohms.
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  #10  
Old 08-14-2006, 07:14 AM
subru92svx subru92svx is offline
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So pretty much check the ohms of the resistor and if it is out of spec. replace it and see if the code goes away and if it is within spec. then its my solenoid valve "A" like code said?
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Old 08-23-2006, 09:42 PM
subru92svx subru92svx is offline
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Ok, I finally got a chance to pull my transmission at school and hopefully find out why my AWD is not working and to replace my flexplate because I was getting a light knocking that sound comming from flexplate area. I have read SVX flexplates are known to crack, but mine looked fine when I pulled it off. Anything else in that area that could make a knocking noise like torque convertor? I read the TCU codes before I pulled it, but the only code it was getting was #11 Which is solenoid A, but like I sad earlier I checked the resistor and it was bad. So I'm gonna guess that its probably just the bad resistor making car say code 11. A new one is on its way thanks to poweredx2. I got my transmission out of the car in about three hours and pulled off the transfer housing. Everything looks perfect though. I pulled the transfer clutch apart to inspect friction dics and steels and they all looked like new. Everything inside transmission looks very clean with no metal chips, fragments, etc. I did however find out that my transmission mount was completely busted and was not holding at all anymore. I already bought a new one though for when I reinstall transmission. Could solenoids or sensors be bad without throwing codes? We have Mitchell On Demand at school and it told me to check resistance through solenoid C. It said should be between 9 and 15ohms. Mine was 13.5 so within spec. It also said a bad solenoid C would cause excessive braking during cornering. Which I believe experienced the other day unless I'm just being retarded. I turned threw a 90 degree corner at about 35mph and gave it gas while comming out of the corner, but car kinda slowed down then sped up once I was threw the turn.Two shops in my area told my just to replace solenoid C while I'm there in the area, but I'm not thrilled to be replaceing a $100 part if its not bad. I need help. Any advice what else could be wrong? Thanks
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  #12  
Old 08-24-2006, 04:06 AM
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[QUOTE=Could solenoids or sensors be bad without throwing codes? Thanks[/QUOTE]

Yes, even though the electric solenoid portion is OK the actual valve seat could be leaking. I have gone to considerable trouble in documenting the details. Have you read and understood? The A solenoid valve does the most work and should normally be the first to be replaced. Even so solenoid C could be faulty.

You have all the required information and only you can make decisions. After all it is your money. With everything in view think about your problem logically. You must appreciate that there is little else anyone can do from afar.

All the best. Trevor.
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