wallyiv

need some help..im a new audi owner of a 1997 a6 avant quatro.
my proublem is im only getting around 300 highway miles a tank! is there anything that could be causeing this issue?? other than the norm of tires, filter, plugs. i do have a egr fault code. would that cause any issues with mileage?
thanks

Luxus Panzer

Try the search button. We can then discuss/elaborate on the things you find.

Lago Blue

Yes an EGR code might indicate there is an issue that would effect mileage.
What is the EGR fault code you have?

Any other codes?

Are the rigid fuel lines under your car metal or plastic?
Are they leaking? Any evidence of fuel leaking on underside of car causing fuel staining (looks like "water-marks") or wetness on the undercoating?
Are the flexible fuel lines in the engine compartment and their connections leak-free?

Do you know how to use the search function here? We can go through some material that has been discussed here in the past. Your problem is not the fuel mileage, that is only the logical end result of required maintenance; or lack thereof.

I'm getting 32 plus mpg(US)high-way, so a calculated:

14.4 gallons(US)('93 model 90Q tank capacity) x 32 = 460 miles /tank full

...if I ran it completely empty.

wallyiv

there is no gas leaks. egr has insufficient flow, it runs great no rough idle. should i pull the egr off and clean it? i have been checking all over the site for help. could you direct me to a certain post?

Lago Blue

Yeah, if it was but that easy.

What to do next. Do some reading (try to skim through everything linked to here briefly, then go back as required), some simple tests, and start to think about going from the simple to the complex. Successful ownership of this car is going to eventually require that you end up with an Intake-manifold that you have had off, for several reasons and maybe more than once; but perhaps not just yet.

I would start with a Mity-Vac and 3 meters of BMW 3mm I.D. vacuum hose. Start leak-checking <i>all</i> your vacuum systems. Replace <i>all</i> the original "soft" hoses, there must be about twenty-seven of them. Capturing, and delivering maximum engine vacuum is what is going to give you the most mileage for your labour.

The code you have may be indicative of a vacuum leak that may also cost you mileage, or it may mean your passage is plugged and that is not costing you nearly as much mileage, or you may have both. Or neither, the insufficient flow may be due to the EGR Valve itself not being opened enough. This may be the valve itself, or the rest of the EGR system whose job it is to deliver engine vacuum to the EGR valve; and bleed it off. Perhaps your EGR Valve's diaphragm is punctured or the valve is stuck closed.

See code 2411 at 12v.org under diagnostic trouble codes. Click on it to expand and read the factory trouble-shooting checklist.

There is a temperature sensor in the EGR passage-way that warms-up when exhaust gas gets recirculated by it. This sensor's signal is interpreted to mean "flow" by the ECM, but it is sensing the exhaust heat.

You may need to read about the EGR Frequency Valve (N18) and the mod (modification) formerly known as "the EGR mod". May the gods help you.

All the above is easily test-able by you. You can read more about the EGR System here:

https://www.audiworld.com/forums/sho...highlight=2411

Link below explains the system operation, you can ignore the fancy VAG-COM stuff if you want and actually operate the EGR Valve by sucking on a length of hose (or use a Mity-Vac, it's inexpensive and you will get a great deal of use out of it; chasing vacuum):

http://www.optisciences.com/fun/egrcode16785.pdf

If the EGR Passage-way is plugged, then the EGR system is simply trying to run more than it usually does, as the sensor (G98) can't warm up and satisfy the system.

If you clean-out the passage, that CEL should disappear if that was the issue, but this won't improve your mileage much.

There are perhaps 4 levels of cleaning people perform, from simple to complex:

a.) Pour or have liquids sucked directly into the Intake-manifold to attempt to dissolve deposits;
b.) Remove EGR Valve alone and do bicycle-cable roto-router procedure;
c.) Remove Intake Manifold, EGR Valve and temperature sensor and simply rod-out the passage-way with a long, sharp object;
d.) As per step c.) above, but in addition; mirror-polish the passage-way.

You can imagine which is the most effective long-term. I have never bothered with method a.). When I first did this, I didn't want to remove the Intake-manifold, so performed method b.) The passage-way was so plugged, it required that I use twist-drills in my bare hands to clear space, just to insert the cable.

link to descriptions of cable method:

https://www.audiworld.com/forums/sho...ight=EGR+cable

https://www.audiworld.com/forums/sho...ight=EGR+cable

http://natwhite.mnsi.net/audi/egr.html

The cable method is still rather crude. Preventative maintenance is so much more effective than reactive maintenance. I now have a mirror-polished passage-way and have done the ski-pole mod to the cam-covers to help keep it that way. I no longer get this code.

Photo shows VAP's recommended EGR Passage Polish tools. The procedure write-up is in the links contained in the link at end of this post.

Looking back, the best method is plan to remove the manifold. If one was to acquire a second manifold, you could prep it and then simply swap it out complete with clean injectors, ICS, etc. That way you will have more time to clean and inspect as you dis-assemble.

The Intake-manifold assembly is certainly a place where you can make some mileage gains:

- the mating surfaces all need to be trued; &
- the mating surfaces all need to be sealed;

(The above two items are going to allow more vacuum delivery to the FPR, allowing it to deliver proper fuel pressure. The elimination of this and any other vacuum and/or un-metered air leaks are going to force the air consumed by the engine to be read by the MAF sensor. This will aid greatly in giving the ECM better engine load data, allowing it to move the mixture closer towards stoichiometric, and thereby getting to hand-off sooner, where the final mixture tweaking control is given over to the O2 sensors alone to do, in closed-loop, and staying there in closed-loop; longer.)

- the injectors need to be sent away for service, so that they all actually close, spray and deliver identically;
- the injectors need to be re-installed with new O-rings to prevent fuel and vacuum leaks, and to prevent fire;

The EGR passage-way needs to be polished, not because it's a great help to mileage (but a fully-functioning EGR System is!), but to lengthen the service interval it otherwise requires, which allows you to spend your precious available time on less repetitive and more productive pursuits, such as;

- the cylinder-head to intake-manifold gasket needs to be used as a template to re-draw the intake-ports in the heads, and that extra material needs to be removed from the head, to allow the injector spray a clean shot at the back of the intake-valve.

There are other preventative-maintenance reasons to have the Intake-manifold off but the above "match to the gasket" one is to improve fuel delivery, and improved mileage is one result of that.

link to Intake-manifold removal tips:

https://www.audiworld.com/forums/sho...ight=EGR+cable

If your not tired of reading you can find more here:

https://www.audiworld.com/forums/sho...hlight=tour+II