Tracker 101: intro to the 4WD air pump
 

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In 1999 and 2000 Suzuki used a stand-alone 4WD controller to operate the air pump for the front differential.
A4 and A6 were inputs, A1 and A3 were outputs and A2 and A5 were power and ground.

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In 2001 an upgraded PCM took over the 4WD controller functions. The two inputs and two outputs were still there. The PCM supplied power and ground.
It worked great.

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Unfortunately the Suzuki draftsmen bungled the PCM internals and those mistakes became part of the Factory Service Manual.

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This is the air pump. It has three components. The motor turns the pump any time
12 volts is applied to pin 3 and the pressure switch contacts are closed. The pressure
switch is operated solely by air pressure. It is not an electro-mechanical device.
The only wires going to it are the ones to the contacts shown above. The contacts
are normally-closed. The third element is the air release valve. It is an electro-mechanical
device. The valve is normally open. When the coil is energized the release valve
closes allowing the pump to build up pressure. When the air pressure reaches
six psi the pressure switch opens and the motor stops. In a good pump the release
valve will hold pressure until the PCM deenergizes the coil. This is what the they
were supposed to draw.

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This is the air pump drawing that got printed into the Suzuki manual instead. They
combined the release valve coil with the pressure switch contacts to form a normally
open relay that does not exist.

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The Chevy draftsmen had no clue how to make sense out of the mess they were
asked to translate. This is the frankendiagram they created for the Chevy service manual.

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This is the 4WD circuit that should have been printed in the Chevy manual.

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The Suzuki person labeling the PCM pinouts seemed to know how it worked. The Chevy guys were just making wild guesses.

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I'll say this for Suzuki. When they make a mistake they commit to it. They carried the 4WD/PCM errors over
to the PCM schematic as well. They may be wrong but they are consistently wrong.

I find this very interesting, but I am not so sure an air-pump driven 4WD system is a good idea. at all, unless it can filter out dust and water. In my experiences with air pumps (smog pumps) the dust would eat them up in a hurry, requiring replacement. One of the best days of my life was when I removed the A.I.R/smog pump from my father's C-60 medium-duty truck, and chucked it in the trash bin after I took a sledgehammer to it. He'd gone through 6 of those things, not knowing that they were NOT required on a medium duty truck at all. I plugged up the intake ports in the exhaust manifolds and since V-belts were in use, it was a piece of cake to dump that POS into the trash bin, never to be seen again. Hoo-Rah!!:).

The pump is usually the problem due to air leaks. I fixed mine but I sure cannot recall the details 7 years later. you have to remove the pump to service it. It is located behind the front bumper area. Follow the air hoses!!

When my pump would not hold pressure, I sent it off to Troy at Refurbished 4x4 Actuator Air Pump Repair for a rebuild. He
charges $132 and I didn't have to splice my connector onto a new pump.

I recently had my pump rebuilt byTroy. After re-install, I found the air intake was plugged and had to be cleaned out. All works good now!

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4WD owners who have never had a problem with their pump may not realize this curved pipe is
the air intake. I know I didn't.

Mine also had a rubber hose that connected to a tiny breather that snapped into the fender well cavity. Metal pipe had accumulated rust inside itself.

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That's interesting. My 2001 air intake stops at item "7." I didn't know item "39" even existed.

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I added this generic solenoid operated release valve symbol to the
4WD air pump schematic for clarity. The release valve is normally
open (plunger up). When the PCM supplies 12 volts, the solenoid
pulls the plunger down so the air passage is blocked. At the same
time, 12 volts is applied to the pump motor. When the air pressure
builds up to 5 psi, the pressure switch opens and the pump motor
stops. But the release valve stays energized until the transfer case
lever is pulled back out of 4WD.

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PCM pin C3-15 provides the power to drive the pump motor.

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Pin 15 on the PCM connector...

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... traces back to pin 3 of IC49.

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IC49 is an SK5151S.


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Pins 1, 2 and 3 act as emitter, base and collector. Battery voltage is supplied to pin 5 and pin 4 is used to monitor device performance.