2006 TDI: 36 to 30 MPG. Why?

[2006YellowTDIBug]

Car: 2006 Beetle TDI, 105000 miles, auto transmission.

When we bought the car, we got 36-38 MPG around town (normal driving). For the last three tanks, we got 30 MPG. While we had teh timing belt replaced at 100,000 miles, the MPG was the same after that.

What to do and check?

Thanks.

[h_2_o]

is it throwing any codes and have you changed the fuel filter in it?

[Blugg]

Have you checked and changed the Fuel Sensor ?



A part that goes quite frequently on the 1.9TDi's

Cheap as chips from the VW Dealers and always in stock due to failing a lot on the Rabbit's too.

[2006YellowTDIBug]

Thanks for the replies. I am slow responding since I thought I would get an email when someone responded (I didnt' get any).

I replaced the CTS (coolant temperature sensor) shortly before mileage tanked because I did get that faulty code. After replacing it (thanks to the help from here, BTW), the code went away.

Once, and only once, I got a glow plug light on (my wife saw it) but it did not stay in and has not recurred. Currently there are no codes or warning lights.

Could it have been a bad tank of diesel at the local station?

[2006YellowTDIBug]

Thanks .... that looks like the CTS I replaced. I have not done a fuel filter. I will look into it.

Originally Posted by Blugg

Have you checked and changed the Fuel Sensor ?



A part that goes quite frequently on the 1.9TDi's

Cheap as chips from the VW Dealers and always in stock due to failing a lot on the Rabbit's too.

[2006YellowTDIBug]

I will look into changing it. I have not done so. Which means that at 105000 miles I am WAY overdue (we owned it since 80000)

[wraithkl626]

I know this maybe waaaay of base, but do you know what shape that transmission is in? I don`t own a tdi or an automatic VW, but my automatic Mazda 626 just went out and before it did the mpg dropped off pretty quickly and it was not slipping or shifting any different prior. The trans pump has gotten very weak and it now slips with a lot of whinning, extra heat,and lower mpg. Time for a mtx swap.

[2006YellowTDIBug]

Originally Posted by wraithkl626

I know this maybe waaaay of base, but do you know what shape that transmission is in? I don`t own a tdi or an automatic VW, but my automatic Mazda 626 just went out and before it did the mpg dropped off pretty quickly and it was not slipping or shifting any different prior. The trans pump has gotten very weak and it now slips with a lot of whinning, extra heat,and lower mpg. Time for a mtx swap.

Thanks. Tranmission is acting fine. I will likely take it in to a non-VW TDI mechanic to look at it.

[Kingcodez]

I don't know much about your engine, but did you check to see if there's blockage in the EGR? In my car (ALH) if you leave the EGR cooler in it will accumulate crud over time and restrict the intake system, like cholesterol lol.

[N41EF]

The EGR shouldn't be that bad on a PD that has only seen ULSD. Have you noticed a decrease in power? On our ALH bug we noticed that fuel milage dropped and power went down, to where the cruise couldn't hold speed on a large hill. Using vagcomm found that the MAF had a spead between actual and requested air flow. A new MAF made things much better.

Just because the check engine light isn't on doesn't mean something isn't throwing a code. Do you know anyone close with a vagcom? Where are you located,

As a rule, people who've never worked on a VW diesel aren't going to have much of a clue, and will throw parts at it chasing it. Replacing the fuel filter if you haven't done it since you've owned it is a good idea. Adding a fuel cleaner like power service or one of the lube moly cleaners available at NAPA. Cleaning the injectors with diesel purge would be another good idea.

You PD engine uses a wierd "torsion Value" to set the cam timing to the crank, if you search for that term on TDICLUB you'll find a post that Frank06 did that explains it. Ifthe car seems to run right and is down on power , has a wierd idle, or bad fuel economy, it's something to check.

[boertje]

It is not uncommon for the PD such as the BEW and BRM engine to loose it's cam with that kind of mileage on the car. Franko6 has a whole write up on this on tdiclub. Also indeed, your torsion value could be off. Mine was set to 3 so I reduced it to 1 and mileage improved. I also have an 06 bug with DSG trans.

[kcfoxie]

If it's the camshaft you'd have a missing at idle, it's be VERY noticeable by now.

I'm betting you have a plugged up fuel filter. When was the last time you replaced it? if you can't answer that, replace it and I bet your mileage comes back.

Based on the mileage you list i'm guessing you've got an automatic. I get well over 40 in town in my manual (that used to be an automatic, and got 34).

[Rubee2006Tdi]

One other thing to be aware of is the DSG autobox that comes on the Tdi's in 06. That tranny is great but MUST be serviced at 40K intervals. and is NOT cheap. But I am told the new transmission costs about 6 grand so 300-400 to service sounds cheap. :-)

For certain check and make sure the service has been done. It should have been done twice already and be nearly ready for it again. Good luck.

[boertje]

Originally Posted by kcfoxie

If it's the camshaft you'd have a missing at idle, it's be VERY noticeable by now.

I'm betting you have a plugged up fuel filter. When was the last time you replaced it? if you can't answer that, replace it and I bet your mileage comes back.

Based on the mileage you list i'm guessing you've got an automatic. I get well over 40 in town in my manual (that used to be an automatic, and got 34).

No, it will not neccessarily miss at idle as the cam might have worn evenly on all lobes. Experienced this first hand. Check the cam lobes...all of them. Check cam followers too. Do check fuel filter as well.
U have an ALH, different animal from the BEW. There is virtually no mileage penalty with the DSG transmission as apposed to the 01M. 1 mile perhaps but that is it.
I have done a few auto to manual swaps on the ALH and a few 5 to 6 speed swaps in bugs.

[Smileybug]

Foxie used to have an '06 Jetta TDI. He knows all about the BEWs and the like

[kcfoxie]

Well it was a BRM... but the BEW is essentially the same.

And, no, from what TDI Clubs reports a PD engine (BEW or BRM, anything later than MY04 is PD-BEW in the Mk4 chasis - New Beetle/Golf/Jetta [to 05.5]).

It always starts with Exhaust #3 and spreads from there. You can check up on TDI Club about that, if you like, it's far more common on the BRM motor but it first cropped up on the BEW in the 04 model year.

This car, boertje, is a 2006 thus it's a PD and not an ALH. ALH's went out of production in 2003.

The DSG is worlds better than the 01m, and it should be seeing high 30s low 40s.

[Smileybug]

Hey, I said BEWs *and the like* Diesel nerd!

[boertje]

Originally Posted by kcfoxie

Well it was a BRM... but the BEW is essentially the same.

And, no, from what TDI Clubs reports a PD engine (BEW or BRM, anything later than MY04 is PD-BEW in the Mk4 chasis - New Beetle/Golf/Jetta [to 05.5]).

It always starts with Exhaust #3 and spreads from there. You can check up on TDI Club about that, if you like, it's far more common on the BRM motor but it first cropped up on the BEW in the 04 model year.

This car, boertje, is a 2006 thus it's a PD and not an ALH. ALH's went out of production in 2003.

The DSG is worlds better than the 01m, and it should be seeing high 30s low 40s.

Hey kcfoxie
Your previous post lists a 2003 bug so I assumed you were coming from an ALH position. BTW, did you go 5 or 6 speed on your swap? Didnt know you had an 06. I have an 06 bug with DSG too and yeah, I know it's a PD and I know too that the ALH went out in 03. The 06 I have is a nice, nice car. Just bought it last July with only 6300 miles on the clock. It was just a baby and now I have it broke in for the most part. First thing i did was to inspect the cam since this car never saw a freeway in its 5 year proir to me owning it. I did know that the BRM was more susceptible on the cam issue. Seems that franko6 has a cam bearing mod that might just save the cam on both the BRM and BEW. Have you looked into that? Looks intriguing.
The 01M trans is indeed a mileage penalty piece of junk. I still have one bug left with the 01M. It's an 03 GL. I'd swap in a six speed if only my daughter could run a stick. So far I have converted my jetta and golf from 01m to the 6 speed and it has just made the cars a pleasure to drive. The best part was the mileage increase 42 mpg before and 50 after. Just converted my latest bug from 5 to 6 speed. 2375 rpm at 80
...now if only I could get better mileage out of my BEW. I average about 43-44 on the freeway which is about 4 mpg better then when I first got the car.

With that said, has the OP checked actual engine temp after warm up? How about EGR function and whether the flap that regulates intake is opening all the way? Malone was investigating this issue on the BEW as to economy that under some instances, that flap would not open all the way nor stay open as it should causing a lower efficiency. This he told me just recently and was also trying to find a way to monitor this with vag-com. Also what of timing as in torsion value? Would be worth to have someone check this. How about power on this car? Is it still normal? If not, turbo? Does the BEW use a snow screen as the ALH did? How about air filter?
I know some of these things are obvious, but this would be my road map.

[cep]

I have had many diesels and many clogged fuel filters. Every one manifested itself in the same fashion--a loss of power, not mileage. In fact, mileage will go up because a restricted filter is the same as putting an egg under the accelerator.

I would suspect winter fuel.

[boertje]

Originally Posted by cep

I have had many diesels and many clogged fuel filters. Every one manifested itself in the same fashion--a loss of power, not mileage. In fact, mileage will go up because a restricted filter is the same as putting an egg under the accelerator.

I would suspect winter fuel.

That's what I thought too but the original post was September.