I used an expansion plug from PepBoys to seal the check valve in case it leaks. But now I am re-thinking my smog pump delete after learning the cat will be ruined without air. My federalized '78 euro has the Neutronics Bosch K-Jetronic Upgrade Kit which converts the K-Jet to a closed loop system. It needs the air pump to function properly. Maybe I should re-federalize my defederalized shark to save the cat? If I delete the air pump I should delete the cat, yes?

 

Jim: What a clean machine.

Toofast: Re Air Pump removal and cat longevity: I guess we need a poll here reflecting actual experience. Reputable sources have said no ill effects from removing pump. I'm assuming not all engines that have cats (everyting after a certain date??) have an air pump. And (some? euro 928s don't have pump). How do their cats survive?

 

I notice Quick Carl uses a cat ... sans smoggie ....

 

I believe all MY '80 US did not have smog pumps. My old 80 US had the fan idler pulley in lieu of the smog pump, and OEM cat in place. They only did it for one year though.

 

........ and ........ the cat .......... doesn't explode ...........

 

Removing the air injection may increase CO emissions, but ought not to affect the life of the converter. The air is injected into the rear section of the factory cat, and any contaminants (coolant, oil, or too much gas) which would reduce it's life would spoil the larger front section first.

Here's a decent writeup I found with a quick google: (Article)

"Modern converters control the three main pollutants by using two different processes: oxidation and reduction. Oxidation/reduction converters have two separate catalyst beds enclosed in a common body. The front half, the reduction catalyst, deals with NOx by pulling the nitrogen off the oxygen and allowing the two elements to recombine as O2 and N2 the same as they existed in the air naturally. CO is handled by the rear-mounted oxidation catalyst, which uses the newly-remade O2 to combine with CO to make CO2. More oxygen boosts the efficiency of the process, so a little air injection here is sometimes used, which is why the air tube is commonly seen halfway down the converter body. It also suggests that a test that shows excessive CO might have an air pump or air injection "plumbing" problem."
...

BTW: Weigh the value of NOx and CO reduction using catylists against the increase in heavy metal pollution (eg. palladium, platinum) from catylists (which can increase the threat of neurological disorders)...

 

That's an excellent point that is stated too rarely.

 

I have deleted my air pump as well. I used a rubber cap with a clamp to seal the check valve at the rear of the passanger side cam tower. Used the same type of cap to seal off the air box port. These rubber caps can be found in multiple sizes at any local parts stores. My cat has also been "gutted", which is causing an irritating resonance under the car. It really gets irritating at about 1900 - 2100 rpm -- seems to really screw up the exhaust note.

By the way, I'm currently using a 21" belt to drive the fan, but there is quite a bit of slack in the belt. Anyone using a shorter belt and if so, where can I find a shorter belt.

 

If the back of the heads is the injections point, as mine was, then those can be sealed with stock parts. It's the same plug as you'll find on the front and readily available. (928intl) Then all plumbing can be removed.

 

I just noticed today, after having to reinstall my pump for a DEQ visit, that the bypass valve dumps air into the airbox* when you go full throttle, not throttle closed. So at WOT, there is no air injection.

Probably since the WOT mixture is rich and open loop...

*The bypass valve is controlled by manifold vacuum; under vacuum it is pushing air into the cat.

 

Idle/Part-Throttle: Air diverted to cat
WOT: Air diverted to airbox
Idle/Part-Throttle: Mixture Stoichiometric
WOT: Mixture rich

Conclusion:
Air diverted away from cats when mixture = rich

Question:
Why is that? Seems counterintuitive to me?

 

heinrich,

I believe one reason for no air injection when rich is to keep the temps down in the cat. The extra fuel actually helps cool the cat at very high speed running!

Also the air injection might be turned off to limit backfires in the exhaust with extra unburned gas present. The engineers must be worried about backfires quite a bit, because there are number of mechanisms to try and prevent them.

On my 8 liter Cadillacs, I had the ignition cut out at highway speed a couple of times. When I restarted the engine while still rolling, I made two different mufflers go from oval to round from the monster backfire!
...

More chemical info I found interesting and lifted from (here).

"In an automobile's exhaust system , a catalytic converter provides an environment for a chemical reaction where unburned hydrocarbons completely combust. Hence the combustion process continues but outside the engine combustion chamber where no useful energy is extracted. Toxic car gases such as unburned hydrocarbon (UHC) and carbon monoxide (CO) would not exist if the fuel to energy conversion in the engine were perfect.

A three-way catalytic converter has three simultaneous tasks:

1. oxidation of carbon monoxide to carbon dioxide: 2CO + O2 ---> 2CO2
2. reduction of nitrogen oxides to nitrogen: NOx ---> O2 + N2
3. oxidation of hydrocarbons (unburnt fuel) to carbon dioxide and water: CnHn+2 + O2 ---> CO2 + H2O

These three reactions are most balanced at the stoichiometric point, where there is a balanced amount of oxygen to fuel in the engine. When there is more oxygen than required, then the system is said to be running lean, and the system is in oxidizing conditions. The above two oxidizing reactions (oxidation of CO and hydrocarbons) are favoured. When there is more fuel than oxygen (stoichiometrically), then the engine is running rich. The reduction of NOx is favoured."