GPJ

01-60 of OBD Multiport Fuel Ignition

GPJ

Maybe you never reset the codes after your initial vacuum leak?

GPJ

As Mr Paul said, you should be ok, BUT.. EGR does limit the amount of NOx, so the cat may be stressed to reduce slightly more NOx...

Mr Paul [T-28]

I did. I will wait and see if they come back.

t0adman2.8

Thanks gents....I'm going to check my CEL codes tonight

VAP

right side engine bank has zero EGR bleed-off from it's exhaust manifold as 100% of all EGR samplings are taken from left bank?

Truth is you can run with or without EGR and still even pass emissions if everything else is in good shape. The exhaust gas being recirculated is a thimble-full volume at most and only intermittently. And performance nor life of ANY component is adversely affected. My EGR valve is a machined "fake" only there to pass the visual portion of the emissions test. And my 1995 12V runs cleaner, emissions-wise than a bone-stock 2002 V6 and only VERY slightly less clean than a stock 2006 V6 which has additional emissions equipment tho my car still easily passes the 2006 standard that are imposed on the later cars. Mine's way way way cleaner than it was when sold off the showroom floor and this with 95k miles on it, gobs of engine mods, stand-alone engine management and an EGR valve that does NOTHING but look like an EGR valve... its all machined aluminum painted flat black with no moving parts and a line into the IM port thats really solid aluminum and not even a "tube" at all!

AudiMick

When the valve opens temps climb accordingly.

GPJ

Mance,

True, EGR is bled off the left side, but the exhaust gasses are fed back into the IM, reducing combustion temperatures and NOx production in all cylinders. I'm surprised you don't see this.

Also, according to AoA's Advanced Engine Performance Diagnostics course, "precombustion NOx control is the primary method of controlling NOx... i.e., retarded timing, _richer mixtures_, and _EGR flow_ all help to reduce NOx." "Post-production NOx control (cat) is only a secondary method of control and even if the cat is working perfectly cannot overcome an engine producing too much NOx."

I'm sure that you have noticed that our engines run rich at certain times when the EGR tends to be closed, and leaner at constant higher rpms with a (more) closed throttle when the EGR valve tends to be open. Interesting observation, don't you think? Later Audi engines that do not have EGR control, AEB, APB, AHA, ATQ, etc., do not run as "rich" at certain times as our AFC/AAH engines do. I believe this is for a reason. Every operating characteristic of our engine is part of the system, and should not be isolated and changed without careful thought.

GPJ

Agreed, that is the proper method with a vag.

VAP

as you've described in real life. That the car even with stock management can be tuned leaner/cleaner and better performing if the EGR falls off and some other things take place. I do understand the "theory" you're touting but it just doesnt work on our cars as well as on some others. And I have plenty of testing and documantation to back it up from EGTemps to tailpipe emissions to wide-band sensor outputs. Our cars are tuned fat as pigs and you don't have to look any further than a tailpipe to see it. Then compare it to my tailpipes before or after stand-alone, BMW tailpipes, Honda or Toyota tailpipes to know which car is cleaner, more efficient and/or making more power per cubic inch. Also compare the emissions threshhold "maximum" numbers compared to most any other car of similar displacement of the era and look how high the 12V is allowed compared to most other cars of the same year. The 12V gets off very easy in terms of comparison.

The system "may" have worked a little better when the cars were new. But the bottom line remains that if the emissions test says you're cleaner than stock. If you feel the increase in power and if your tailpipe is light tan in color instead of thick, puffy, sooty carbon black it makes clinging to your theory closer to Pavlovian than real. And much of that soot can be easily explained away by combustion AND exhaust temps being dramatically over-cool to begin with and thats why there's SO much exhaust condensation and subsequent EGR passage blockage going on.