Drop of mileage after EGR adaptation

ijust bought an 03 golf tdi
filled it up for the first time got 44.9 mpg
and its an auto!! 5000 mi. i am psyched!!no mods
hey i used to have a 69 sb i know what you mean.. (pos fI)
i seem to remember some kind of bacolite brackets
that held the injectors in place
they kept cracking ...pita /images/graemlins/frown.gif

I have consistently gotten between 2 to 3 mpgs more on CA fuel after returning my EGR to stock. I am a longtime TDI owner ('00 Golf). I am a mileage hawk. I can emphatically say that, if you want higher mpgs, avoid the EGR mod.

The EGR computer mod obviously affects other things in the programming and timing maps. I have also experienced a large drop in mileage with the mod, going from an average 40mpg to 31mpg with no other changes. At idle, my car is inhaling 450mg up from 370 (according to the VAG 250-370 guide range) and this is with stock airfilter and no snorkel tube.

I cannot explain the gigantic increase in suction, but I will be returning my EGR setting to stock and see what that changes. My car is "incapable" of re-breathing any of it's exhaust, let's just leave it at that. *cough*steelplate*cough*

So, on an automatic, any theories why at idle it would be so hungry for air? Timing is within range, or slightly above the range, belt (and engine) have 65K on them. Otherwise stock, 40 cetane dino juice.

--Jim

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The EGR computer mod obviously affects other things in the programming and timing maps.



I cannot explain the gigantic increase in suction, but I will be returning my EGR setting to stock and see what that changes. My car is "incapable" of re-breathing any of it's exhaust, let's just leave it at that.



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Jim, I have returned our Passat to the default EGR value and the MPG has pretty much returned to what I'd consider normal (42 - 44 mpg). The fuel economy over the past 12 -18 months had been erratic and not for the better.

As you hint, I also believe this "EGR mod" is affecting more operating parameters than we're aware of and it doesn't put a stop to the intake clogging.

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The EGR computer mod obviously affects other things in the programming and timing maps.

I cannot explain the gigantic increase in suction, but I will be returning my EGR setting to stock and see what that changes. My car is "incapable" of re-breathing any of it's exhaust, let's just leave it at that.



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Jim, I have returned our Passat to the default EGR value and the MPG has pretty much returned to what I'd consider normal (42 - 44 mpg). The fuel economy over the past 12 -18 months had been erratic and not for the better.

As you hint, I also believe this "EGR mod" is affecting more operating parameters than we're aware of and it doesn't put a stop to the intake clogging.

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My thoughts exactly. Look here.

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(Snip) Jim, I have returned our Passat to the default EGR value and the MPG has pretty much returned to what I'd consider normal (42 - 44 mpg). The fuel economy over the past 12 -18 months had been erratic and not for the better. (snip)

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__. This is interesting. I've averaged about 59-60 MPG over the past 10K miles on summer fuel and about 56-58 MPG on winter fuel over the past winter. It would be interesting to see what mileage I'd get if I put the EGR back to stock. It was reset at a mini-GTG near Potomac mills when I had about 2800 miles on the car.
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Jim... I just installed the Old Navy VVC filter on my car and went back to stock EGR. Not enough of a sample to see if my mileage has changed... but in the past, I have not seen a noticable difference.

However... and this is just a thought... I wonder if the MAF specified numbers are accurate after the EGR mod has been done? In other words... maybe the EGR mod "fools" the computer into thinking thenumbers are higher, when in fact they are the same as normal... or maybe just not as far off as the computer thinks. Just a thought.

BTW... I pulled the CCV breather hose off and cleaned it really well (I should have done this right when I put the O.N. CCV filter on there). Anyway... it's been about 500 miles of my normal driving since I cleaned it. The CCV filter has lots of oil in it... but I pulled the breather hose last night and it's still dry! /images/graemlins/smile.gif

Now, once I get some bio back into my car, I can really stop worrying about my intake clogging!

Ok, here are the initial readings from VAG:
Changing the EGR setting DOES change other settings, indicated most noticably by the "MAF Specified" setting. This number is the expectation of the computer, and is used to compute the fuel mapping, and most probably the timing and injection quantities. If the engine is expecting air X and you tell it to expect X+Y (with no egr) then it will add more fuel to try and balance, hence the loss of economy. Conversely, if you tell it to expect X-Y (Lots of EGR, but the EGR is blocked) then it should REDUCE fueling under idle or part throttle, leading to a leaner mix. I am currently testing this theory and will report any findings or strange behavior. The change should not be lean enough for any damage to occur, such as burning pistons or overheating operation. Diesels operate insanely lean anyway, so the only change I might see would be a drop in power while cruising, when max power is not being asked for anyway. No big deal.

Just to start things off, I DO believe I have noticed a change already, the car seemed a bit quicker with the EGR set to "max" operation. Hmm. *scratches chin*

Now for the numbers: All readings were at idle with a warm engine, started from cold and idled for 10 minutes (yes they do warm up at idle!)

With the EGR modified:
MAF specified. 230-270 VAG range, 380/385 says the computer.
MAF actual. 230-270 VAG range 440/470 actual flow. Duty cycle 4.8%

Testing settings in adaptation:
31768 (Max EGR setting) specifies 180mg/R, 460 actual flow
32768 (stock EGR) specifies 280mg/R 460 actual flow
33768 (everyone's favorite mod setting) specifies 380mg/R with 460 actual.

Like I said, I don't know why my car is SO hungry for air, but here are the numbers for group one from the measuring blocks, where you check on the timing settings. Maybe there is another number that says something interesting to someone else:
043 064 000 031 098 204 081 132 130 135


Thoughts?

--Jim

I have two tdi's. A '00 Jetta and a '03 Jetta Wagon. Both 5spd. I noticed poorer fuel mileage when I did the EGR mod on both. I cleaned the intake on the '00 and that wasn't too bad. I set them both back to stock and the mileage has improved by about 2mpg. I installed ONCCV's on both. We will see how that goes.

When I installed my ONCCV, I returned the EGR to stock. I ran a full tank (over 800 miles) of good fuel. About 1/3 of the tank was highway driving, which is unusual for me. On the highway, I set the cruise at 60 MPH... yes 60. I wanted to see how much I could improve my mileage! The rest of the tank was my normal daily commute.

The last three tanks (with EGR mod) were all on my normal commute, and I got between 49 and 51 MPG. After going back to stock, I got 51 MPG. I really was expecting better, not only because of the stock EGR, but also because of the 200+ miles at 60 MPH. Hmmm... I think I'll go back to the modded EGR setting.

I don't doubt that some folks are seeing a difference... but I certainly do not. I think everybody here will admit that these cars can be very different. There are people who seem to drive the same way, in the same environment, and one gets 38 MPG while the other gets 55 MPG. Anyway, if it's going to possibly eliminate the need for an intake cleaning, or even just delay it, it's worth it to me.

Update: I have received an engine code, EGR Excessive Flow.

From research online at an Audi site, I surmise that this code relates not to the EGR valve and it's inabilty to pass gasses, but to a minor leak from the exhaust tube at the other side of the blocking plate I am using. The blocking plate is inserted right under the EGR itself, and must not be totally sealing the exhaust tube.

From my research, there appears to be a venturi (narrow point) inside the exhaust pathway to the EGR, and sensors on both sides of this venturi. Since the car knows when the EGR is supposed to be open or not, if these sensors register a pressure drop from gas escaping somewhere, then the computer thinks the EGR is stuck open. Not the case, but at least it's someplace to start looking. I'm going to unbolt the blocking plate and look for a carbon (dirt) trail where a leak would be likely, and see about making a new gasket from black silicone instead of the fiber one in there now. I'm sure that is where the leak is.

Beyond that, my mileage HAS improved since resetting the computer back to the "stock" EGR setting, even tho the EGR duty cycle still reads 4%. interesting, the only other thing that is noticably different is the MAF expected airflow, listed in my previous post. I plan on changing the computer setting to the MAX EGR level, 31768 and see if my mileage goes up even further, since the car will only be expecting (and fueling) for a much lesser amount of air than at the min-EGR setting we all know and love. This will only be used by the computer at idle or part throttle, so I shouldn't even notice the change, except at the pump.

--Jim

What about trying EGR at maximum setting and see if MPG could go even higher? Maybe I'll be the tester for a least 1 tank. Can't hurt right?

Hey Jim,
Any new info on the lates changes "EGR 31768" you made?

Well, My mileage has not been the best, I can definetly hear an exhaust leak from the blocking plate, I plan on fixing that tomorrow. Other than that, no obvious detriment to having the EGR set "high" and I should have more info in a bit. Let me get a few tanks through the car, since I also just today got 4 new shoes for it too.

--Jim

Moderator - Old thread but seems to be enough controversy that the TDI-FAQ par. "J" may be questionable info. Your call.

trj said:

Moderator - Old thread but seems to be enough controversy that the TDI-FAQ par. "J" may be questionable info. Your call.

Click to expand...

I'll add my experiences here as well and state that BOTH my cars' fuel mileage dropped when I did the tweak: my wife, who was heck-bent on beating my fuel mileage was really upset, so it was in no way a subtle drop; I'd read so much in favor of this, and it totally convinced me, that I'd told her that there was NO way that the change made the mileage worse! I set back to stock and BOTH cars are now back to running right around 50mpg. And, I apologized to my wife!

Perhaps there's something else that is supposed to be tweaked in concert with this, but as far as I have seen there is nothing mentioned.

Maybe we need to call in Myth Busters on this one?