Quote:
Originally Posted by NiftySVX
I apologize, both Trevor and I, among others, are intimately familiar with this particular circuit as it is unlike any other circuit on the car. We tend to get long winded and overly technical about it (especially me on the long winded part  )
Long story short the resistor's purpose is not to change anything exactly, instead it is meant to help prolong the life of the A solenoid. How it does this, while interesting, is not something relevant to what you're trying to figure out. As we mentioned, the A solenoid controls line pressure. However, when the resistor is not in the circuit, it has the effect of raising line pressure. This is unlikely to cause immediate damage, in fact, some remove the resistor on purpose for this reason. BUT, it is not operating as it was designed.
I want to suggest again that you have the transmission shop connect a line pressure gauge and measure line pressure at the control port and at the transfer port on the extension housing as a first step. All of the problems you are describing are symptoms of abnormal readings that would be found in these tests, and this is the first step in diagnosing your problem
FWD is not a "mode" and you should never drive the car like this unless it is absolutely necessary. If the car drives fine in AWD, leave it there. |
A long winded message very worthy of continuing.
Thank goodness for someone with a brain. I have had to continually put up with all manner of argument and wrong information posted by Harvey over the resistor circuit, since I posted some time ago the information which follows.
Also great that at long last, someone is pushing the use of a pressure gauge when trouble shooting the transmission. Not doing so is like pissing about with electrics in the car, without ensuring that adequate battery voltage is on tap.
I have obtained a nice gauge, which I intend to mount permanently in the car, as a safety measure and for obtaining readings of interest.
THE DROPPING RESISTOR CIRCUIT.
It will be apparent that the sudden on off pulse width modulated duty to which solenoid valve “A” is subject, tends to cause what could be called a hammering of the valve seat, even though this is largely reduced/damped by the controlled fluid flow.
The dropping resistor introduces a second series of current pulses, applied in parallel with the control signal. These pulses are applied across the off cycles, so as 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, mean that during the closing period the voltage does not fall completely to zero, so as to reduce a closing shock.
This second series of pulses must be at a lower level than the control signal, hence the dropping resistor. A resistor with a high current rating is required, which could not be mounted within the TCU enclosure.
It will be appreciated that increasing the resistance in the circuit, or opening the circuit by omitting the dropping resistor, has two outcomes. Firstly the voltage during the closed time becomes zero, thus increasing the line pressure and making shifts more abrupt. Secondly, as an undesirable issue, shock loads applied to the valve are increased.
It is a recognized fact, that the line pressure control solenoid is usually the first to fail, due to having to fulfill by far the most arduous duty by operating continuously at 50 cps. Failure is usually mechanical, resulting in the valve seat not closing properly and a reduction in line pressure. The end result can be drastic, especially in respect of transmission friction surfaces.
The resistor should measure between 9 and 15 ohms to be within specifications, and is usually very close to 12 ohms.