Leaking Air Pump causing lean condition???

[kookers]

Hi All...

Wanted to see if you all agree with this diagnosis: My faulty air pump is throwing off my mix and causing bad gas mileage.

To explain....

I was testing to see that my Secondary Air System was working properly. I discovered that the "Integral Stop Valve" solenoid that is built into the air pump doesn't react to a 12v signal... (no click or anything) and you can blow through the hose all the time. (the motor does work however)

When my engine is running in closed loop and the air pump is not on, there still can be felt a suction going into the input hose of the air pump. (I guess a venturi effect from the exhaust?). I think it supposed to be completely blocked off when the pump is off.

I monitored the voltage on my O2 sensor, and when I blocked the pump input hose with my thumb, the voltage on the 02 sensor immediately shoots up to to about 800mv for about 5 seconds, then levels out.

To my thinking, this indicates an always lean condition... one that is causing too much fuel to be put into the mix.... and that I need to replace the pump or fix the internal stop valve...

Does anybody concur with this?

[geoffinbc]

Its possible. Depending on the vehicle it is easily removed or repaired.

[TGP37]

I agree with your observations. Adding fresh O2 will make the PCM think the fuel delivered is not enough and will up the fuel trims to compensate.

But there is no problem with the fuel delivery, generally. So the engine runs rich as you guessed.

Ironically, you probably didn't notice much power loss in the top end. The fuel trims are not calculated in PE Mode. Might have fouled up the plugs some.

[kookers]

Ironically, you probably didn't notice much power loss in the top end. The fuel trims are not calculated in PE Mode. Might have fouled up the plugs some.

You're right I didn't. But yesterday I temporarily deleted the pump, tightly sealing the tubes off and the engine is absolutely noticeably smoother both at idle and just cruising around streets. Who knows how long this has affected my engine. (almost 180k on it)

I need to pass smog this year in California, so I do need to fix the pump. I took it apart but the internal stop valve is completely frozen and the rubber seal is gone.

Rather than spend $150 or more on a new pump, I scanned the local junkyard for them. Found three on older Camaros and ALL had the exact same problem. I have to imagine that this problem has plagued most 3.4L engines out there. I think the issue is probably the check valve between the pump and the exhaust manifold.... Most people have water come in from the exhaust, but living in dry SoCal I think it was just exhaust gasses that did the damage. They should make that check valve a yearly or bi-yearly service item IMHO.

P.S. Plugs were clean.