hello everyone, this is my first time posting here
the forum has always lead me through my problems until this one
the car is a 1998 a4 2.8 AHA engine
i have been getting the P0411 for about 2 years
never thought it's that important until now that i cant pass inspection

P0411 secondary air injection flow - incorrect flow

i checked all the vacuum lines and they are all good
my secondary air pump still sucks in air as i put my hand over the hose
my mechanic has a fairly new pump from a 1.8t jetta
so i replaced mine with the jetta pump and still no fix
also took my combi valve down to clean, and bought a used pair of them and non of them fix the problem

now i ran out of ideas on what to fix next as i cant afford to buy new pump or valves

the car is also making a high pitch clicking noise only at low rev when the car is accelerating, mostly at low speed low rev on 1st and 2nd gears
if the car is parked, the noise will only come out if i suddenly rev the engine hard for less than a second in the begining of the rev, which makes it hard to locate where its coming from, but when the car is moving it is really annoying

someone at my gas station garage down the street said it sould like an air leak
but i cant find out where is leaking, although it really sounds like a bad valve to me

my questions are :

1) will the 1.8t jetta air pump be enough to pump enough air into my v6
engine? (the pumps look identical)
should i get a new pump?
2) is there any way to test my combi valves?
should i buy brand new ones?
i have curruntly own 3 pairs of them but donno how to test them
3) is the noise a vacuum leak? if so how do i find the leak or fix it?

i have spent so many hours trying to fix the car and get my inspection
with the weather getting colder and colder i dont really have much time to fix it in my parking lot
any suggestion or advice will be greatly appreciated
thank you in advance

 

As far as I know, the code you're getting has to be either due to the pump, the combi valve or a vacuum line. I'd suggest to replace all your vacuum lines first to see what happens. Sometimes there could be a crack or hole in one of them that you don't see.

 

Another possibility is one of the secondary O2 sensors - the ECU uses them to read the airflow from the SAP system. I know the B5 Passat, and therefore I'd assume the A4 as well, has a range issue on the after-cat O2s (the coding for their allowable range of operation in closed-loop is ridiculously tight, and can be widened by a dealer ECU reflash for $100). That may be at fault here too, or you could have a secondary O2 starting to head down the drain.

 

Could an exhaust leak cause this code? I know I have one and also have this code.

 

Yes, the vacuum created behind an exhaust pulse can draw outside air into the system. That'll go through the cat, get measured by the secondary O2 sensor, and register as improper airflow since it'll skew the readings taken by the sensor.