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Misdiagnosis on Mazda G4A-EL / Ford F4EAT

At times it's easy to make a misdiagnosis on Mazda G4A-EL / Ford F4EAT units.

For example, a vehicle has a problem that the engine stalls when the manual selector is placed in the Drive range. Although this may appear to be a lockup problem it may be engine related.

The cause may be a cracked air cleaner-to-intake-manifold tube allowing cold air to rush into the throttle body and mass airflow sensor causing the engine to stumble and die. This normally happens only in the Drive position because when Drive is selected the engine and the transmission shift toward the firewall, stretching the tube apart. When Reverse is selected the engine and the transmission are shifted away from the firewall, sealing up the cracks in the tube.

Remove the air cleaner-to-intake-manifold tube between the throttle body and the aircleaner box, and inspect for cracks as shown in Figure 1. If cracks are found, duct tape can be used to temporary fix until the tube can be replaced. Secure hose clamps and make sure that all engine and transmission mounts are good.

After overhaul, the vehicles with these units may exhibit a pulsating sensation on forward application, wrong-gear starts, downshifts to 1st at higher speeds or no Reverse. The O.D or Hold light also may be flashing.

The cause may be that the wire harness conduit, or protective coating, was removed and the solenoid harness connecters now may be attached to the wrong solenoid.

Figure 2 shows you solenoid identification and the location on the valve body. The Mazda part numbers are also shown.

Figure 3 shows the wire colors for the solenoids and solenoid connectors and terminal identification.

TERMINAL	IDENTIFICATION	WIRE COLOUR	CONNECTOR COLOUR
1	Temp Sensor	White	Yellow
2	Line Pressure	Blue	Green
3	3-2 Downshift	Black	Black
4	3-4 Shift	Brown	Brown
5	1-2 Shift	Black	Black
6	Temp Sensor	White	Yellow
7	N/A	N/A	N/A
8	Lock-up	Yellow	Green
9	Lock-up Control	White	Black
10	2-3 Shift	Green	Green

Vehicles that have no reverse before or after overhaul can have four possible causes:

A faulty vehicle-speed sensor, signaling the computer may apply the 1-2 shift solenoid and block the passage of fluid to the low reverse clutch (see figure 4).
A stuck 1-2 shift valve or leaky bore plug at the end of the 1-2 shift-valve lineup allowing the 1-2 shift valve to block the passage of fluid to the low reverse clutch (see figure 4).
Note: This may also cause 2nd gear starts in drive.
A 1-2 solenoid that is stuck open allowing the 1-2 shift valve to block the passage of fluid to the low reverse clutch (see figure 4).
Note: This may also cause 2nd gear starts in drive.
A low-reverse or reverse-clutch failure.

For a quick check, unplug the harness connector from the vehicle-speed sensor and place the selector in the reverse position (see figure 5). If reverse engages, go to correction 1 and the most likely possibilities. If reverse does not engage, go to corrections 2, 3 and 4 for the most-likely possibilities.

Corrections
Diagrams 5 and 6

Replace the vehicle-speed sensor
Inspect the 1-2 shift valve as shown in figure 6 for free movement in its bore. Air check the 1-2 shift valve from the hole where the 1-2 shift solenoid is placed. Listen for the sound of the 1-2 shift valve snapping back and forth and ensure no air leakage from the bore plug at the end of the 1-2 shift-valve lineup.
Apply air pressure to the 1-2 shift solenoid, as shown in figure 7, and ensure that there is no leakage when there is no voltage applied to the solenoid. Replace if necessary.
Note: It may be necessary to apply 12 volts to the solenoid several times to ensure that the solenoid is closing every time the voltage is removed.
Inspect the 0-ring on the solenoid and replace if necessary.
Inspect low-reverse or reverse-clutch assemblies for wear and repair as needed.

This article reproduced with permission from Transmission Digest
For subscription information contact Mike Turner
Tel: 001 417 866 3917 Fax: 001 417 866 2781

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