I am having problems removing my air pump. I am at the point where the front of the pump is the only point where the pump is attached to the mounting bracket. At that attachment point I find not a bolt but what looks like a piece of metal "tube" with a slit (kind of a circlip I guess) lengthwise that is inserted into the mounting bracket. How in the world do I get this thing off? Do I need to remove the ac compressor as well to get the pump out? I posted a picture on my web page of the attachment point in question. Any advise would be greatly appreciated.


Carl Lindberg
1986.5 928S 5-speed


It is a sleeve that tightens as the bolt is tightened. Get a screw driver between it and the pump and force it toward the front of the car. It should all come apart then,... I think.
Mark Grasser
78 #358


I just looked at mine. It's lying on the floor because I removed it last week. There is a steel insert in the pump housing that is flush with the end of the pump. There is a split sleeve in the bracket that tightens against the pump. It should not be into the pump, unless someone really cranked on the bolt. I think a little bit of whacking on the bracket with the bolt removed might help after you let the WD work for as while.
Mark Grasser
78 #358


The diverter valve dumps the air pump air to the airbox at WOT so as to not overheat the exhaust system.

I was under the impression that with modern high flow cats, the extra air injection that the air pump provides is completely unnecessary. The air pump only functions on start up to help add air to the cats to help them warm up the cats for better function more quickly.

So, given that the air pump valve shuts off after the car warms up, I'm not sure how it would affect a properly running car. Given that I was doing the timing belt and installing a Porkensioner, it made sense to get the cheaper non air pump bracket and get rid of the extra component.
1987 Guards Red 928 S4, GTS mirrors, color matching rear spoiler, V8- dream toy

The 928 air pump runs all the time. The valve under the airbox diverts air from the cats (or head on ROW engines) to the airbox at WOT so the stock over-rich WOT mixture cools the exhaust, instead of burning.

Air pump delete? The air pump bracket is used to hold the AC compressor too. That needs some rivets to compensate the air pump bracket when it is deleted.

Originally Posted by 76FJ55
If you look at the tensioner for the old air pump you will find a washer that I determined to be the perfect replacement for the space the tensioner are used to consume. Circled in red Item 14 from the attached section of the parts catalog. You can't miss it when you remove the pump.

That's what I use. Thoughtful of Porsche to include the delete part on the standard assembly.

If you don't have that part, you need a 6mm | 1/4" washer with a 8mm | 5/16" hole (or two 1/8").

On the later 928 the air pump injects into the mid part of the cat not up by the head as in the early cars. the cat is separated in to two sections the first I believe is to reduce NOx and the second chamber to oxidize CO. My understanding is that the air is injected in front of the second section to increase the oxygen potention and promote the oxidation reaction from CO to CO2. All this takes place after the O2 sensor so it should have no effect on mixture.
85 928S AT Fully Porkenized, X-pipe
My airpump is disabled and I have 200 cell cats and I passed emissions testing. Come to think of it, I think Porsche actually stated emissions testing should be done with the airpump temporarily disabled - somebody correct me if I am wrong here.
1989 S4 auto

The effects of air pump deletion vary greatly from year to year, as the pumps do different jobs.

On the 1978, the air is injected into the exhaust ports, where it assists in more complete combustion of the hydrocarbons (HC) and carbon monoxide (CO). Both of these will be higher if the pump is disabled or removed. Oxides of nitrogen (NOx) is not affected by the air pump, but only by exhaust gas recirculation (EGR).

On the 1989, the air is injected between the first and second stages of the cat. The first stage is a reduction stage to reduce NOx. The second stage is an oxidizing stage to oxidize HC and CO. Removing the air pump will lower, but not eliminate, the effectiveness of the cat in lowering HC and CO.
Wally Plumley