Nice piece of kit for those who don't want to source a used unit every 3 or 4 years. Nice work.

I would recommend doing what ever service is needed to keep the air pump system working properly. It's not really that big problem and really no good reason to eliminate it. You will most likely creating bigger problems for yourself or whoever you sell the vehicle to down the road.

Maybe check/replace the air pump check valve on the exhaust manifold. AFAIK it's usually the problem and starts leaking exhaust gases back to the air pump. In my case my air pump got quiet again some time after replacing the check valve and I sent the new pump back to FCP euro 2 years later.

^That's exactly what typically happens. Exhaust gases corrode the pump by causing condensation to build up and rust it from the inside. I always replace the valve, vacuum line servicing the valve, and the SAP when I've seen a failure. Cost for used is typically about $75 for both from a local breaker.

AFAIK, you won't damage anything in any great hurry. The SAP system was designed to get the cats up to temp faster to lower emissions. I don't think them warming up slower will do anything negative to them or other systems. Personally, I replace them because cost is so minimal.

:iagree: Another reason to replace the secondary air pump is without it one ones vehicle is contributing to pollution. I think we should all do our part, even as small a contribution as a working SAP.

I wonder if his m54 is polluting less without an SAP than our v8's do with all the emissions stuff working? It certainly gets better gas mileage.

I agree with you in principle though. But that's the reason we still have all our diesel x5's emission gear in place and have not tuned it.

Happy to say, I now see how to pull out the old Whistler, disconnecting the bracket that its mounted too with 3 x 10mm short bolts. I'm going to order the new part. The cheap $50 ebay part is tempting. If it last two years I think it would be worth it vs $200 for the pierburg. My car isn't worth much...

So, do you all think it's not really the pump, but maybe the check valve? That seems easy enough to replace...

You probably need to replace the check valve anyway so do that first and see if the pump quiets down.

Is there a way to know which one is my issue? I'd rather not buy both. If the check valve was bad, would it make noise after the pump motor turns off? The high pitch squeal definitely seems to come from the blower part.

I read that without the SAP the first 5-10 minutes of driving will pollute more than the next few hours so clearly it’s a significant part of pollution reduction. It's stupid expensive to get a new one but if you can source a decent used one it's the route I would take.

The bypass for track use makes more sense however. It's quite silly to apply highway emission rules to racing.

Back to the topic: if you get 90 seconds of sound like the car is trying to hover thats the classic symptom of the pump bearing shot.