I Lost My EPC! - Transmission Digest

I Lost My EPC!

The AODE/4R70W transmission has a problem with wear in the pressure-regulator-valve bore that can cause a reduction or complete loss of EPC pressure when the unit is hot. This equates to no or minimal line rise, causing the transmission to have medium- to full-throttle slipping in gear and sliding shifts. Once a pressure gauge has revealed that EPC pressure remains near 0 at any throttle opening (as well as when the transmission is unplugged), the technician usually replaces the EPC solenoid, yet the problem remains.

I Lost My EPC!

Technically Speaking

Author: Wayne Colonna, Technical Editor

Bore wear can cause loss of pressure in AODE/4R70W

Technically Speaking

  • Author: Wayne Colonna, Technical Editor

Bore wear can cause loss of pressure in AODE/4R70W

The AODE/4R70W transmission has a problem with wear in the pressure-regulator-valve bore that can cause a reduction or complete loss of EPC pressure when the unit is hot. This equates to no or minimal line rise, causing the transmission to have medium- to full-throttle slipping in gear and sliding shifts.

Once a pressure gauge has revealed that EPC pressure remains near 0 at any throttle opening (as well as when the transmission is unplugged), the technician usually replaces the EPC solenoid, yet the problem remains.

A look at the pressure-regulator valve (Figure 1) may not always reveal a problem. Sometimes it may offer a clue with wear on a land as shown in Figure 2. It also may be difficult to spot the wear problem by looking down the bore (see Figure 3).

But when you refer to a hydraulic schematic, you will see that EPC pressure is routed to the pressure regulator valve alongside a circuit Ford identifies as the boost circuit (see Figure 4).

In actuality, this circuit is routed back to the inlet side of the pump, as figures 5 through 8 reveal. So if the pressure-regulator-valve bore wears enough between these two circuits, EPC pressure gets sucked away by the pump, preventing any line rise with throttle opening (see Figure 9).

A quick test to determine whether this is the cause of erratic or no EPC pressure is to remove the transmission pan and filter and blow compressed air into the TV pressure port as shown in Figure 10. Seeing air and fluid blow out around the EPC solenoid area as seen in figures 11 and 12 is normal, so do not be alarmed here. But if you see air and fluid blow out of the filter as illustrated in figures 13 and 14, you have just discovered this bore-wear problem causing the loss of EPC pressure. At this time no aftermarket fixes are available; you’ll need to replace the valve body to correct this condition.

One extra note: If bore wear is minimal, this problem may go unnoticed. If the unit is experiencing premature wear of the forward clutch, this may be the reason.

Many thanks to Chris Colucci of CNS Transmissions in Walnut, Miss., for not giving up until this problem was located.

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