1995Qsport

case proven i had same code pop up numerous times. popped the hood checked all lines and adjusted the screw to the left bout 1 turn (didnt know what way to turn it) car ran perfect.. hissing noise was gone and cel never popped up.. no cold start hesitation or anything.. im still gonna clean my passage and stuff but im happy now.. thank you

sdb90

that I had that bugged the hell outta me (not too far down page) I can use this to help explain myself better and maybe someone can help me. The line I have completely open is the connection at the EGRFV...the one that (in picture) has a black hose from it. I have the other end [of where that line would be] capped off at the TBody. This pics makes it appear that I can just as easily reconnect the line from point a to point b regardless of my intake lacking vac connections....kindda makes me feel stupid. But can someone explain whats happening with that line hanging open vs. if I simply reconnect it as it seems I should? why is my car running fine with that line wide open. thanks all.

austinado16

It just allows the EGR solenoid valve to actuate properly since one side of the plunger is under vacuum.

Lago Blue

further to what austinado16 said, its a source of atmosheric pressure that relieves the applied vacuum when the EGR F/V is "off" & allows the EGRV to close.

Some call this the Egr Mod &amp; are happily running their cars this way.<ul><li><a href="https://forums.audiworld.com/12v/msgs/16813.phtml">EGR Mod</a></li></ul>

austinado16

Personally, I think having that fitting tied to the plenum is the huge contributor to the black gunk that glogs the EGR solenoid and it's hoses, restrictor valves, etc.

As you pointed out in your tests, you found a lot of black crap in the system blocking what limited vacuum is allowed through to begin with.

We've all seen the crud that builds up in the valve cover vent pipes, and then makes its way inside the plenum....and then into the intake manifold where it plugs everything up. Same thing is happening inside the EGR solenoid.

Lago Blue

... yes, like the translucent one on the I/M C/O Valve. I want to see if both of those can be made to function here. Is the I/M C/O V just a different colour?

Re: the dirt, another reason to do the cam cover breathers.

Further, The "why" of the mod &amp; the normal (as opposed to test) mode of the EGR system (as described in the resons for the mod) are what I need to know more about. I thought the normal mode was strictly controlled by the duty cycle of the EGR F/V.

sdb90

I am still a little confused. so ideally, the flow path comes FROM the plenum connection into the EGRFV and NOT from the EGRFV TO the plenum via the [black] vac line. Without realizing it I have then successfully completed the documented EGR modification, no?

If this is true, then what purpose is the EGRFV serving now and/or what function, if any, am I dissabling by having this mod?

thanks guys

Lago Blue

...yes you've done the mod.

To the 2nd (a very good question), I don't think I have the definative answer but here goes:

the EGR F/V functions (IMHO) exactly as before, but with a cleaner atmospheric pressure (vacuum relieving) air supply. Some may think that plenum vacuum is read &amp; transmitted through this black line &amp; helps determine when the EGRV is tested but I am not so sure. Some EGR Systems use intake vacuum amplification to control the EGRV, I don't believe this is one of those. One reason for this is where that black line connects to the plenum on the B4, is there a spot between the MAF &amp; T/B that could sense less vacuum? Probably not. A read through of the Mityvac manual speaks to some examples of the above.

Did Audi connect it this way because it is a possible un-metered air leak point into the engine if the EGR F/V should fail mechanically (the very type of seal failure austinado16 has illustrated) &amp; it was open to atmosphere (like the I/M C/O valve is)?

Caution, wild-*** speculation follows:
Perhaps some have seen some relief by doing this mod because the EGR F/V may tend to clean itself out inside when the supply of dirty relief air has been removed &amp; replaced with a clean one, allowing its' function to recover.

In my case, the EGR F/V internal seal has failed &amp; it only works correctly intermittantly &amp; requires replacement because it does not seal reliably against vacuum, &amp; leaks vacuum whether the ECU is asking the EGRV to open <b>or not</b>. This vacuum is also constantly leaking at the EGR F/V port which connects to that black hose.

sdb90

now does this mean, with the EGR mod done, that adjusting the VAC Reducing screw can/will still yeild results (whether good or bad), or is this screw now without a purpose.

thanks again for the input.

Lago Blue

...as before, fully in (clock-wise) should be most restricted, not entirely closing the passage IIRC (don't strip out the plastic housing threads!). Fully open ...(perhaps somewhere near screw-head top fully flush with raised plastic surround? Haven't figured that out yet.) ...still reduces the vacuum from that delivered from the intake manifold; &amp; this adjusted amount will be reduced further (up-stream?) by the fixed black in-line ("x" orifice) restrictor at the EGR F/V end of the brown line.

Full I/M vacuum should not be nearly required nor would it be good for the long term health of your EGRV diaphram (see also the spec.'s in the manual). Despite the "x" restrictor, I could not reccomend by-passing this vacuum reducing valve, as I have not measured it's output alone. I don't yet have a reason to bypass the adjustable valve.

Found my adjusting screw O-ring being pulled off (up!) the screw -again- (and leaking vacuum, again!). There is a slight relief cut in the shank of the screw under the head &amp; above the shank holes. Re-positioned the O-ring &amp; re-installed the screw. Cleaned &amp; -re-sealed- the screw head in its raised plastic surround (with some goop) to prevent further leaks till my new EGR F/V arrives.

I am also wondering if this vacuum leak is causing slightly higher fuel pressures (&amp; consequently; delivery) than we would want &amp; get otherwise? I believe full vacuum is required to get the FPR delivery down to 3.5 bar from 4.0. As the FPR shares the I/M vacuum source with this system, this is the reason for my suspicion, but I have not been able to measure that yet.

Lastly, I did read in an OBD II Training Manual that all the vacuum operated EGRV's are either positive or negative exhaust system back-pressure types, &amp; that engine load will vary the diaphram control vacuum required (required vacuum in the brown line) to properly operate the EGRV. That is probably the reason for this adjusting screw, as these (EGRV's &amp; EGR F/V's) are used on different cars, they are probably set, and the screw -sealed-, at the factory for their specific application.