Another SAI question
 

Full disclosure...I posted basically this same post on a couple of other 986 boards...as I'm new to the car, I'm also new to these forums.

I'm a new Boxster owner, having purchased a 2003 986 S a month or so ago. It is a 49k mile car, all records, IMS done 1000 miles ago (PO had done just before extended warranty expired, to enhance resale value). I'm really pleased with the car. As for me, I am a decent parts replacer and set up guy (autocross SCCA at National level, currently running a Van Diemen RF88, and also am finishing a bare-metal up restomod on my '66 Sunbeam Tiger), but get pretty lost with modern electronics and emissions systems.

I started noticing an electric motor sound on start up recently, which through searching this forum (and others) I've determined is the secondary air injection pump. Seems it is getting that higher pitched noise that indicates bearings are either dry or worn. I have also searched and determined that: 1) a Porsche oem part is very expensive 2) you can get a new Bosch replacement part for around $545 3) they are readily available on ebay, used, for anywhere from $100-300. Sound about right?

But, here's the thing...I first noticed the noise last week, when it was lasting approximately 30 seconds or so, before cycling off. Now, this week, while the quality of the noise hasn't changed at all, it seems like it is lasting longer. I don't think it is temperature related, as it lasted just as long when I started up this afternoon, after being parked outside in the sun on a warm day, as it did this morning in the 55 degree garage. In any case, it seems like it is more of a 1 minute plus type deal, now, and I believe it was about half that a few days ago.

So, the question: If the SAI is cycling longer, all other factors being equal, what might that indicate?

My plan is to remove and clean/lubricate, as much as possible. If that doesn't work, let it die, if that's what it is going to do, and then replace. Not sure if that means a used part...anyone have any experience with buying used pumps? But, before I would replace, I'd like to figure out if the pump motor is going south for some other reason, if that makes sense.

Thoughts?

Thanks-Mike

Mike,

The SAI system turns on based on the engine temperature (coolant temp) and the intake air temp (and the delta temp value between these two). This typically happens when the car starts up. Newer vehicles also have the SAI kick in sometimes when the car is idling.

Also, the system may have some clogs which are reducing the amount of fresh air being injected into the exhaust manifold, but not enough to trigger a CEL -- you may want to check the system before buying anything to make sure that the pump is indeed approaching failure.

Regards,
paul...

Thanks for the response and input, Paul.

Something else suggested was that the length of time the SAI pump runs is kind of inversely related to ambient temperature...thought being that in colder temps, the DME gives a richer mixture, which leads to more unburned fuel available to mix with the injected air, lighting off the cats faster. I can see the logic and it jibes with my experience: morning temps have been a little milder this week and the SAI has seemed to run just a little longer. I don't have any CEL or other problems and the pump cycles off within a reasonable time (45 seconds this morning). I'm still thinking the pump motor has recently become louder, but it doesn't really sound too distressed, so I'll play it by ear for now...no pun intended ;)

Can I assume that the SAI is different than the engine compartment cooling fan? I never hear an electric motor running upon startup but if I restart a warm/hot engine, an electric motor (fan?) turns on and runs most of the time except on the highway. Natural ventilation must occur at highway speeds.

Your assumption is correct, as SAI is for engine emission control and only runs for a very short time.

Regards,
paul...