EGR duty changes in Vag-Com ?

Doug R

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Sep 2, 2002
Location
Clinton, Iowa
Just hooked my Vag-Com for the first time. In watching the MAF flow and EGR duty as the car idles I notice that MAF setpoint and measured are about 270 and the EGR duty is about 65%. After several minutes of idle it the EGR duty goes to 4.8% and MAF measured of course goes up to 450 or so, but the MAF setpoint is still at 270. If you bump the throttle the EGR comes back on. I'm on a desktop so I can't take it on the road to see what it does. If I make the duty cycle change will it then be 4.8% all the time? I know you guys can explain whats going on. Thanks.
 

wkendrvr

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Start the vehicle, goose the go pedal, look at the egr. It will still be closed. If you are really unconvinced have someone else goose the go pedal. You will see NO CHANGE in EGR... (I am referring to watching the egr open/close) You are confusing DUTY CYCLE with % OPENING OF EGR (which there is no monitorable measuring block that we know of?) You really need to watch the requested MAF vs ACTUAL. If requested = actual then EGR = OFF (you can test this by changing back. you will see requested != actual, the difference being the EGR)

Make sense?

[ September 29, 2002, 16:04: Message edited by: wkendrvr ]
 

wkendrvr

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I meant to say, look at it physically, not monitoring it.

[ September 29, 2002, 16:11: Message edited by: wkendrvr ]
 

GoFaster

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Making the adaptation mod won't turn the EGR off completely at idle.

By the way, pay no attention to the duty cycle. 4.8% means "off", 80+% means "on", but in between that the number is meaningless. Look at the actual amount of air indicated by the MAF sensor, not the duty cycle.
 

wkendrvr

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Originally posted by GoFaster:
Making the adaptation mod won't turn the EGR off completely at idle.
<font size="2" face="Verdana, Helvetica, sans-serif">You need to look. On my 02, it appears to do just that. The EGR does NOT move.
 

GoFaster

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Betcha you've got a duff MAF sensor if it's turning the EGR all the way off.

At idle, stock actual MAF reading should be around 250 mg/stroke. Adapted, it should be around 370 mg/stroke. After a 2 minute period of idling it should go to around 480 mg/stroke which is what it draws in when the EGR is REALLY off.

If you are not getting that increase from 370 to 480 mg/stroke after 2 minutes of idling, either your intake manifold is badly clogged, or the cam timing is WAY off, or (most likely) the MAF is toast.
 

GoFaster

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One other thing, in order to make these measurements, the engine has to be at normal operating temperature, in NEUTRAL, and all major accessories have to be switched off.

Auto tranny in "drive" at idle will specify more air and draw in more air due to the load on the engine from the torque converter.
 

schnabba

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interestingly enough, the bentley breakdown of how the EGR works has some blurb about how the valve seat is cone shaped and has several cross sectional sizes - and the computer uses N18 to create pulsed vacuum to precisely control "all the different EGR positions for each cross sectional opening" or something to that effect. This would imply that it is not just an open or shut condition.

So - to see if this is possible from a mechanical standpoint, I used a vacuum pump to measure the vacuum and the amount of opening on the EGR valve.

NOTE: I give ranges because I know my guage will measure differences, I just don't know how absolutely accurate it is - the point is not the accuracy of the guage itself, just are there really different positions possible at different levels of vacuum?



1. It doesn't start moving until about 10" of mercury.

2. Then, at 11-12", the first part of the cone shaped seat is visible.

3. At 13-14", the cylindrical bottom section is still in the cone shaped seat

4. and at 15" the bottom of the top part of the valve is even with the top of the cone shaped seat.

5. anything above 15" just pulls the valve farther from the seat, until you hit 19" and the valve is fully retracted.

It looked to me like there were maybe 4-5 variations possible? Starting between 10-11" of mercury, and every inch of mercury until 15" the cone valve is restricting the cone shaped seat at a different point until it clears the seat completely between 15-16".

If anyone is *really* interested in this, I can take pictures of it as I do this (that would involve about "4 cans" - see footnote about # of cans per experiment).



regardless of what this might indicate, I am with wkendrvr and gofaster - have someone watch it as it is stock, then set it to 33768 and see the difference. Something fun would be to set it to the lower limit of 31768 and watch it there too.



Footnote: this was a "2 can experiment" meaning it took me 2 cans of beer to complete.
 

GoFaster

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Originally posted by wkendrvr:
I meant to say, look at it physically, not monitoring it.
<font size="2" face="Verdana, Helvetica, sans-serif">You can't physically see the EGR mechanism. It is totally enclosed. Don't confuse it with the anti-shudder mechanism, which only operates when the engine is switched off.
 

wkendrvr

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Originally posted by GoFaster:
</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by wkendrvr:
I meant to say, look at it physically, not monitoring it.
<font size="2" face="Verdana, Helvetica, sans-serif">You can't physically see the EGR mechanism. It is totally enclosed. Don't confuse it with the anti-shudder mechanism, which only operates when the engine is switched off.</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Doh! I bet that is what I was looking at.

Note to self - Think Diesel !

Thanks for the correction...
 

schnabba

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no, I had to do some welding afterwards (making some stupid tools for the eventual timing belt change), so the experiment was limited to 2 cans, the other cans came AFTER the experiment, and after the welding.
 

A. Meyer

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Jul 3, 2001
Location
Chapel Hill, NC
On another thread, in this forum, "What about diesel trucks?", there was a comment that when the EGR is is turned off, there is not enough heat to warm the passengers except at high engine outputs. Is this true? Has anybody experienced this?
 

VeeDubTDI

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A. Meyer, I hadn't really thought about it, but the EGR cooler is connected to the supply lines to the passenger compartment heater core. So, if you disable it, I suppose you'd get a bit less heat, although I've never really paid attention.

edit: it may be connected to the return line instead of the supply line, I'd have to look at it again to know for sure. If it is connected to the return line, then it's no big deal.

[ October 02, 2002, 09:49: Message edited by: VeeDubTDI ]
 

A. Meyer

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I think this mod was first brought up on TDICLUB a few months ago during the warm weather. Since it's just starting to cool off in some parts of NA although I had to use the A/C today, we'll find out soon enough if the mod has unintended consequences. I hope not.
 
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