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Old 08-05-2018, 07:24 PM   #1
6spd68
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Default Secondary air injection system

Hello everyone! I need some help diagnosing my secondary air system. I just replaced the air pump and noticed that I have back pressure out of it after the system shuts off. I have vacuum going to the switch and going to the diverter valve during warm-up and when the air pump shuts down I still have vacuum going to the diverter valve. I also noticed that I have about 14.4 volts at the switch during the 30 second warm-up and when the air pump shuts down the voltage drops to 4.3 volts.

Why do I have voltage after the system shuts down? It seems like I should just replace the switch but I would like to be sure before I just throw money at it. I measured the ohms and it was about 44. When I disconnect the vacuum line going to the diverter valve it closes and I get no back pressure. Also, I have seen the richpin video, that's how I got this far

Thanks in advance, this forum is the best!

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Old 08-05-2018, 08:58 PM   #2
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Default Re: Secondary air injection system

Back pressure refers to positive pressure. Vacuum is vacuum. Either a vacuum exists (supplied from the intake manifold only when the engine's running) or not. Blower pressure, when the blower is running, supplies air to the exhaust system when the combination valve opens, feeding air (from the electric air pump) into the exhaust manifold to help heat up the catalytic converter.

Maybe some info can help from the service manual.

The AIR system is used to reduce hydrocarbons (HC), carbon monoxide (CO) and oxides of nitrogen (NOX) exhaust emissions by heating up the catalytic converters quicker on cold engine start-up. The conversion of exhaust emissions to carbon dioxide (CO2) and water can occur sooner as the catalytic converter reach the normal operating temperature around 527C (981F). The AIR system consists of:

*Air pump (1)
*Check valve (2)
*Air pump solenoid (3)
*Combination valve (4)
*Air pipe and hose (5)
*Vacuum hose (6)
*Air pump relay - located in underhood fuse block (UHFB). (7)
*Powertrain control module (PCM) - located underhood between the battery and power brake booster. (8)

The air pump is a permanently lubricated turbine type pump which requires no periodic maintenance. The PCM runs the air pump for a certain length of time when the engine is started within a certain ECT range. When the air pump is commanded ON, the PCM will command an internal driver ON which pulls the air pump relay circuit to ground allowing current to flow to the air pump.

The air pump solenoid is used to control vacuum to the combination valve. When the air pump relay is commanded ON, air pump running), the PCM will wait a short amount of time to command the air pump solenoid ON. The PCM turns the solenoid ON by controlling an internal driver that pulls the solenoid circuit to ground. The PCM waits to turn the solenoid ON in order for the air pump to pressurize which keeps exhaust gas from entering the air pump.

When the air pump and air pump solenoid are turned ON, vacuum to the combination valve will allow the spring loaded diaphragm, upper valve in the combination valve, to be pulled up. This will allow pressurized air from the air pump to flow around the reed valve, lower valve in combination valve, to the exhaust manifold.

Before the PCM commands the air pump relay OFF, it will first command the air pump solenoid OFF and wait a short amount of time before it commands the relay OFF. This keeps exhaust gas from entering the air pump.
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Old 08-05-2018, 10:54 PM   #3
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Default Re: Secondary air injection system

Thanks for the info fdryer. I'm getting exhaust into my air pump. That was the back pressure that I was referring to. The diverter valve is operating correctly. My solenoid may be the problem but I just wanted to make sure before I spent any money. Could it be stuck open and allow vacuum to pass through and keep the diverter valve open even after the computer tells it to turn off? When I measured the voltage at the connector it was 14.4V at start up, then it drops to 4.3V when the air pump shuts off. Is 4.3V enough to keep the solenoid open? When I shut the car off it drops to zero volts as it should. Do you know if I can measure the resistance to see if the solenoid is good. I did and got 44 ohms but I didn't have anything to reference that to

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Old 08-06-2018, 08:15 AM   #4
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Default Re: Secondary air injection system

If you are seeing vacuum at the diverter valve after the air pump shuts off, then that solenoid switch is likely stuck open. Operating in this state will trash the new air pump, with hot exhaust flowing into it all the time.

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Old 08-06-2018, 11:17 AM   #5
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Default Re: Secondary air injection system

That's what I was thinking, I definitely don't want to destroy my new air pump. My new solenoid should arrive tomorrow. I'll let you know if that's it. It's weird that it's stuck open instead of the other way but I guess it could happen. I wish I knew why the voltage remained after the system shuts down. Anybody else ever measure this and have the same results?

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Old 08-06-2018, 03:38 PM   #6
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Default Re: Secondary air injection system

Electronic circuits can be confusing if not familiar with some quirks. Electronics sometimes forgoes using a relay to power solenoids. When this occurs, a power transistor is used. When an electronic circuit switches a power transistor off, residual voltage may be seen on the output side, where you're measuring at the solenoid connection. This is residual voltage with zero current behind it. With zero current at the wire, the solenoid isn't powered. Ignore it. Ask you need to know is if the solenoid powers up and if it opens or closes its own valve.

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Old 08-08-2018, 06:55 PM   #7
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Default Re: Secondary air injection system

I installed the new solenoid last night and everything is working as it should. Thanks for all of the advice. I guess the solenoid bring stuck open is what caused the air pump to fail in the first place

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Old 08-09-2018, 09:14 AM   #8
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Default Re: Secondary air injection system

Glad you got it sorted. This system is a pain. Honestly, if I add up all the time I've spent fixing my Saturn, over 50% of it would be related to the secondary air injection system.

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