924Board.org

cookies409 · Joined: 21 Apr 2011 Posts: 8 Location: Sandy, Utah, USA

I purchased a 1979 924 yesterday and went to go do emissions and inspection today and it failed because it is running to rich. He said the exhaust itself was too rich and had twice the amount of CO. My air pump does not have a belt. Will getting my air pump working help my fuel combust better in the engine and dilute the exhaust with added clean air?

cookies409 · Joined: 21 Apr 2011 Posts: 8 Location: Sandy, Utah, USA

hmm Well does anyone know what the air pump actually does for the engine?

Smoothie · Posted: Thu Apr 21, 2011 11:09 pm Post subject:

Not 100% sure about the air pumps' function - vaguely recalling it injects fresh air into the hot exhaust just at/after the exhaust manifold, and it affects the gasses there by reducing NOx..? -Or does it supply oxygen to continue the combustion process, and reduce HC..??

Anyway...assuming all vacuum leaks have been eliminated, and other components are functioning correctly (WUR, AAV, CSV(not leaky), injectors(good atomization), plugs, wires cap, rotor good, etc), I would adjust the A:F mix. On a fully warmed engine - counterclockwise to lean until it stumbles, then back toward rich just until it smooths out. The difference between too rich stumbling and too lean stumbling is not much - maybe 45 degrees or less, so zeroing in on a good setting requires very slight turns of the adjustment.. -And don't leave it too lean and stumbly - that means combustion is not complete and while your CO may pass, your HC reading will be high. -So find the midpoint between too rich and too lean, then get on the lean side of the midpoint, but again, avoid the stumbles.

If your state also tests for NOx, that further complicates things and you'd need to fine tune it further by taking the adjustment a bit richer. This is because as you go leaner, NOx goes up while CO and HC are going down. -And the opposite applies - as you go richer, NOx goes down while CO and HC go up.
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

Smoothie · Posted: Thu Apr 21, 2011 11:30 pm Post subject:

Here's some air pump info - http://tech.oldsgmail.com/emis_AIR.php .
Apparently they work along with a dual bed catalytic converter, injecting air at the center of the cat, to affect its' second bed and further reduce CO and HC.
The first bed reduces all three - NOx, CO, and HC.

If you have a functioning cat, that's another story - they function with a very slightly rich A:F mix.
-And obviously don't bother with the air pump if you don't have a good cat..
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

cookies409 · Joined: 21 Apr 2011 Posts: 8 Location: Sandy, Utah, USA

how do i adjust the air to fuel ratio?

Smoothie · Posted: Thu Apr 21, 2011 11:59 pm Post subject:

This is interesting - http://www.asashop.org/autoinc/oct97/techtotech.htm
It shows that a functioning cat is way more important than a functioning air pump.

Your model and year are often need. You can put that information in the signature area of your profile.

The adjustment is via a small plugged hole just next to the fuel distributor. Down the hole is a screw that's on a swinging arm (so while adjusting, be carefull not to exert downward pressure on it as this affects the mix also) - a 3mm Allen wrench is used. Be careful to not drop it in there..
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"..it's made in Germany. You know the Germans always make good stuff."

'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

cookies409 · Joined: 21 Apr 2011 Posts: 8 Location: Sandy, Utah, USA

Thank you for all of the information!! I will start with the air to fuel ratio and work down to the catalytic converter if necessary. Once again thanks for the help and information.
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1979 Porsche 924

cookies409 · Joined: 21 Apr 2011 Posts: 8 Location: Sandy, Utah, USA

I just found a great site with tons of information about emissions and gases. It is http://www.autoshop101.com/forms/h56.pdf
If anyone else is having emissions problems check that site out.
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1979 Porsche 924

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

Cookies,

Per Bosch tech training, don't touch mixture until system and control pressure have been verified with a proper tester.
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

Captain_Kirk · Joined: 17 Dec 2009 Posts: 243 Location: Colbert, WA

Maybe just pick up an air pump belt from NAPA, put it on and see what happens. If everything else is the same as it was, maybe the PO just left off the belt. Worth a try.
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1977 924na BlackSeaRD.com Torque Tube SuperBearings, Xenon air dam, 200# Weltmeister springs, Bursch header, 944 exhaust, Audi throttle body