My 1998 tdi Jetta fuel millage is gone way down

Hello my name is Josh my car is a bone stock 1998 jetta tdi/w 5 speed. It is my daily driver I have put 30,000 plus miles on the car I have been doing the regular maintenance a watter pump, fixed a boost leak some injector return lines,ect ,ect now I filled up my tank ran some errands and I couldn't believe how fast my car is going thru fuel. I thought I broke a fuel return line or had a bad leak some where. I checked for leaks the injection pump is dry and all my fuel lines are good. Now I'm at a loss the car runs good does not smoke so I didn't think it was an injector... I'm not sure what it could be. I thought there was a write up on this forum about what to check on your A3 if getting poor mpg but I can't seem to find it. Any help will be greatly appreciated... I know something is way off but it's running strong not smoking just burning fuel twice as fast as normal...

do you have a vagcom cable and VCDS? you need to scan and see what various values like timing, IQ, boost logs, and so forth. this is by far the best way as its fast, easy and tells allot about the car with almost no work at all. Start here.

When you say "I couldn't believe how fast my car is going thru fuel." Whats the MPG?

I don't normally calculate my fuel mileage BUT when I put 30 bucks worth in my tank I can normally drive for 3/4weeks. I put 30 bucks in like I normally do and I ran some errands and the car burned up a 1/4 tank just like that I had just got home when I noticed it said it killed a 1/4 tank wile running errands. Normally with the most driving I do all day my fuel gage would move just the width of the needle.
On road trips my car gets 50 mpg in town I'm around 33 mpg
But I can tell something is off with my fuel consumption.

Is this the first tank this happened? Maybe something is wrong with the gauge or sender. Wait til the next tank or two before you panic. If it's not leaking or smoking, your mpg is probably still the same.

Get some solid mpg info, total miles and amount of fuel consumed vs 3-4 weeks. Amount of time doesn't really tell us that much. It could be a problem but without having some numbers to look at it's hard to say.

Further, the gauge isn't all that reliable anyway. I've found that my mk3 liked to have fuel disappear faster around the middle of the tank vs the top or bottom, it's just the nature of the fuel level senders in these.

Steve

Yeah I'm going to start calculating my fuel mileage. BUT honest know my car something seems off with it. It seem a bit sluggish. I'm hoping my intake is not clogged from the egr system. I drove to Novato today that's a trip I do all the time. That trip my fuel gauge would normally move literally less than 1/8 of a tank about the width of the needle on the fuel gauge is all I would move. And today my car burned 1/4 tank on a 2 hour round trip all highway.

I was hoping some one on here could point me in the direction of a thread I saw on here years ago it was a list of things to check if your fuel milage is down/ basic maintenance stuff really

turbodieseldyke said:

Is this the first tank this happened? Maybe something is wrong with the gauge or sender. Wait til the next tank or two before you panic. If it's not leaking or smoking, your mpg is probably still the same.

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Yes this is the first tank this has happened to. if the third injector went bad and made the car run rich would it be enough of a difference to make the car smoke?

I don't think it's the fuel gage or the sender on account that it is reading normally it not going too high or too it's staying with the fuel leve. It not dropping off anything else

Year back, i used to fill up at a local station that has a truck pump, you will get $0.45 each gallon discount if you buy at least 25 gallons of diesel at the truck pump. I already had 5x 5 gallon fuel containers. So naturally i took advantage. I would fill up each container with exactly 5 gallons then would fill my car up to the top last. mid fill the pump started pumping air and no fuel. i didnt notice until i started the car to write down the mileage. saw the tank was 1/2 empty but the pump said i ran a full amount. Pump ran dry on me. lol
Its not too common but it does happen to some people where the pump screwed up and pumps air instead. since your not paying attention to mileage, maybe something like this happened to you as well but only now are seeing a decrease.
Most tanks when filled to the op dont start moving the needle until a few gallons are used up.
MAYBE you thought you put 14 gallons in but only actually filled up with 10~ but the pump still said 14. See what im getting at.

Anyways, probably not the issue but still you need to go though at least 2 tanks and get some data before you start ordering parts.