Daniel5691

My PO (the world's greatest PO by the way...) had a cat-delete exhaust installed on my 1981 928S. No cats.
Does the air pump now serve any useful or significant function?

Thanks for your help!!!


Dan

bureau13

I believe that was it's only purpose in life. You can get rid of it!

Dave928S

The pump was fitted to non cat euro cars as well ... such as my 82.

As I understand it, it was only fitted to improve emissions, by injecting air into the exhaust ports, to promote combustion of unburnt gases.

I removed mine and found that emissions were still acceptable, with the motor in proper tune.

Get rid of it, along with all the distribution and control plumbing that goes with it, and fit plugs into the ports at the back of the heads (which are identical to the front plugs).

bureau13

Interesting...I had no idea non-cat cars had it.

Dave928S

The difference is marked between the 16V and 32V.

The 16V inject air into a runner in each head, which connects via a small hole to each exhaust port. The air is injected at a point where temps are still high, and the extra air (oxygen) on its own can achieve some 'after-burn'. Cats or no cats and that will still happen. The cats will just give a secondary 'after-burn'.

The 32V injection point is down at the cats and aids the catalytic 'after-burn'. Take out the cats and the air injection, at that lower temperature point in the exhaust system, will be doing a bit more 'dilution' than 'after-burning'.

Alan

It is very likely that at this age the Air Pump pumps ~almost nothing - so on that basis alone - it probably serves no useful function.

On my GTS I removed the air pump and tested it off the car - it is almost useless - and made a lot of noise. My emissions test results are unchanged... The emissions may be worse for a while at startup than Vs. a 'new' condition car - but Vs. an old car with an aged air pump that does almost nothing... um well...

Just get rid of it.

I now have a new vacuum pump there that actually does something...

Alan

SMTCapeCod

Of course, if you pull and pitch it that likely scratches all California buyers and those from Cali-compliant states from your list, if you decide to sell it. But I'd agree barring that which may be a non-issue, it isn't doing anything positive. I fail to see what the negative is that makes it worth the time to yank it though.

mike77

I have mine disconnected since I installed an x-pipe. I left everything in place but left the pump belt off. I've noticed a rattle since then and think it is the disconnected plumbing so will remove at some point.

I haven't plugged anything up on mine. Is that an issue?

FredR

The air pumps were fitted on non cat models like mine that operated in a region where leaded gasoline was still being used when they were sold. When I investigated their reason for being it seemed it was simply a dodge to comply with legislation and served no real world purpose whatsoever.

Maybe they are of more significance on cat models and it would be interesting to know if deletion causes problems for residents of California who I understand Porsche designed the system to meet their specific requirements [the tightest in the world at that time I understand].

Rgds

Fred

hacker-pschorr

The few cars I've worked on with electronically controlled air pumps were all based on engine (and possibly exhaust) temperature and only ran on cold start-up.

The only way I can forsee removing the pump causing an emission testing issue is if the tech knows it's supposed to be there. We all know to test these cars fully warmed up when the pump serves no purpose.

Mrmerlin

In the state of PA if it had an airpump then it must still have the air pump to pass the visual test.

NOTE a visual test is to verify that cats and pump and plumbing are still in place,
it doesnt have to work and the pipe emissions are not tested.
NOTE you also need the tank inlet unleaded collar fitted

hacker-pschorr

What a joke.

So your car can pass with hallowed out CATS and a disconnected air pump while running at 10:1

Meanwhile, a Greg Brown tuned engine with aftermarket cats and no air pump with a tail-pipe emission far better than any stock 928 is not in compliance.

......and people wonder why I don't give much care to emission regulations.

I like what Wisconsin did for the corner of the stat with emission testing. They determined the number of pre ODB-II cars on the road for regular use was statistically insignificant. The testing procedures and regulations were costing the state so much money (rolling road) they went to a simple code check. You pull up, they plug in a code reader, no codes or pending codes....you pass.
Everything made before 1996 is exempt.

MFranke

Take it off and save the parts in case you sell. Also the small machine screws can be spares for your PS pump.

You can get rid of the little filter on the front too and take off the cap. Then you will have a nice beer holder for when you work on your car.

GlenL

This is an unusual observation. Can you say more?

Vilhuer

Having working pump will cause problems in local emission test. For test to be acceptable air ratio must be at proper area. Pump messes up that ratio on both cat and non car cars. Only way to get cars to pass is to block vacuum line to valve which controls where pump air goes. It needs to go to air cleaner box or car will not pass.

Blocking vacuum is not allowed by rules. This means its impossible to get any properly working 928 to pass inspection if inspector knows what he's doing. Result is those cars are taken to local official dealer where one guy who knows what to do runs exact same test on similar machine, blocks exact same vacuum line and prints out exact same result inspection station would have gotten if they allowed vacuum line to be blocked.

Thats how things work officially in here. Good thing is that only very few inspectors care wha its in engine bay as long as emission test looks good and there are no turbos or SC installed.