The smog pump is a low-pressure, high-volume, engine-driven, blade-type air pump. Its purpose on vehicles equipped with a two-way cat (CO and HC) is to pump air into the exhaust manifolds under certain conditions in order to continue the burning process and reduce HC and CO emissions. On vehicles equipped with a three-way cat (HC, CO and NOx) it pumps air into the cat in order to assist the cat's reduction of these pollutants.

There is no reason for pumping air into the intake system. However, on those systems that pump air into the exhaust manifolds, the pumped air must be diverted on overrun (when you close the throttle and coast), or there will be an "after fire" (sometimes erroneously called a "backfire") in the manifold. There is a vacuum-operated diverter valve that does this job. On American cars, this valve dumped thru a small muffler mounted on the pump. On the 928, it dumps into the air cleaner, but there is no functional reason for it to do so other than noise reduction.

Wally Plumley
928 Specialists
================

The air pump is there to help exhaust gas emissions improve, especially at idle. Some 928 owners had trouble with the pump and deleted it. It takes only little energy from the engine so you could consider to keep it and fix the bearings when they fail.

Here's the device connection we are talking about:

If you have exhaust gas check on annual inspection you may need to stop the pump pushing air (O2) into the exhaust. This will make the Lambda value show excessive O2 and could trigger a fault condition (Lambda should be at 1 and obviously if you push extra air the lambda value will be off).

It easy to unplug the vacuum line that opens the valve. At high vacuum (car in idle or little gas) the valve sends air into the exhaust to burn existing HC and CO, at low vacuum it sends air into the air filter housing. If you lease the vacuum connection open you may lose vacuum so plugging it with a stick of cone makes sense. Doing this is easier that removing the hose I think ?

Theo
1992 Porsche 928 GTS Midnight blue
The Netherlands
http://jenniskens.livedsl.nl
http://928gts.jenniskens.eu
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At 09:08 AM 4/24/01, Gerhard Van Zyl wrote:
>I recently had to change the fan belt on my '84 928S because it broke. The PO had replaced the air pump with a jockey pulley to accommodate the cooling fan belt. The bearings on the jockey pulley seized, the shaft slid out, and the belt broke.
>I got a used air pump and replaced the jockey pulley with it.
>
>My questions are:
>1. Is this the right terminology for this pump?

Yes.

>2. What are the functions of this pump?

The air pump is a high-volume, low-pressure vane pump that pumps air into the exhaust system to help burn pollutants.

>3. Where do the pipes on this pump connect to?

The inlet to the pump comes from the air pump filter, located low on the right side on the inner fender panel on early cars, and top center above the radiator on later cars.  The outlet of the pump is routed to the exhaust system, except on overrun (coast), when it is dumped into the bottom of the air filter housing instead. The routing is done by a valve located near the right valve cover.

>4. Does this pump have any influence on performance?

Very, very little. The pump requires very little power to turn, and the air pumped in the exhaust doesn't affect the engine at all.


>Also, when one purchase a maintenance kit (Tune Up Kit) for the 928, it includes an "Additional Pump Filter" or "Air pump Filter"  amongst other things. Could you please tell me what this Air pump filter is for, if it is related to the above mentioned air pump, and where it goes?

The air pump filter keeps dirt out of the pump to improve its life. On your car, there should be a metal canister  (with a wing nut!) on the right side of the engine compartment, at about the front of the tire, down low (inside the engine compartment). On later cars, the filter is top center of the radiator.

Wally Plumley
928 Specialists

===============

Greg,

I rebuilt mine with a bearing from a local bearing shop. The number I used is BCA203-FF 6203-2RS.
The important number is the 6203-2RS. Mine cost $5.56. There may be a Ford bearing, but this one does not scream at me like the old one.

Ken

=========

Disassembly procedure: http://members.rennlist.com/mgrasser/

http://members.rennlist.com/mgrasser/airpumprebuild.htm

How does one get the pulley mounting piece off the shaft? Checked Mark Grasser's page and he goes right by it. Got the pulley off fine, but can't get any further on the front.

Glen
'80 Euro S

Glen,
Step 2. I don't remember it but if I made a tool for it it wasn't easy.
Simply a flat piece of 1/4inch steel with three holes. Still in my "special tools" drawer.

Step 2: I made a puller to remove the pressed on bushing which the pulley bolts to. It is a piece of 1/4 x 2 inch steel about 12 inches long. Three holes were drilled to match the threaded holes in the bushing. By gradually tightening the bolts and installing a 1/4 inch nut under it after bottoming out I was easily able to remove it.

Mark Grasser
78 928 #358

==========Mark,

Color me confused...

I removed the belt pulley (three bolts) and there's the hub. Like six holes on it with three threaded. In the middle is a thing I'd expect to be a hut or bolt. Unfortunately, it's round with a small round hole in the middle. Several tries with vice grips could not unscrew the "bolt"  from the hub, or hub from shaft or anything.

On your page for this, and in the notes below, it sounds like the special tool removes the bearing from the case. Or is the hub pressed on?

Mine was squeaking. With the back off and paddles out, it still does.
It sounds like it's the "scaper" bar along the barrel. Just would like to clean and lube the insides. I'm just using it as a tensioner with the rest of the piping removed. Paddles are in the out basket.

Glen
'80 Euro S

>   I removed the belt pulley (three bolts) and there's the hub. Like six holes on it with three threaded. In the middle is a thing I'd expect to  be a hut or bolt. Unfortunately, it's round with a small round hole in  the middle.
I think the piece you speak of here is actually the shaft and yes I think it is pressed on. The tool is used to press the shaft out. The three bolts on the puller go into the threads in the flange.

>   Mine was squeaking. With the back off and paddles out, it still does. It sounds like it's the "scaper" bar along the barrel. Just would  like to clean and lube the insides. I'm just using it as a tensioner with the rest of the piping removed. Paddles are in the out basket.

When you get it apart simply remove the paddles and toss them.
 

===============

Ken Postma posted the following on 5/14/2002:

"I rebuilt mine with a bearing from a local bearing shop. The number I used is BCA203-FF 6203-2RS. The important number is the 6203-2RS. Mine cost $5.56. There may be a Ford bearing, but this one does not scream at me like the old one."

As for a belt to use, bypassing the pump, Todd posted this on 3/14/2006:

"I found a belt that works perfectly - a GATES 6821 Lawnmower drive belt - which was green and not toothed. It also looked a little too fat, but it works great. No problems after two years and several thousand miles of driving, no noticeable wear on the belt, no squealing. It has stayed perfectly tight. Since there is no adjustment you have to loosen then fan bracket, slip the belt on, then it will go tight as you bolt the fan bracket back on.

Gates 6821. If you cant find it at the auto store, check Sears!"

I remember I rebuilt mine years ago at low cost. The tricky part is that when you disassemble the pump it has some weird parts that you better photograph before you take them apart or you may never figure out how to put it back together. You will need bearing pulling tools to complete the job.

Dan Shapiro
'82 5 speed