(New to me) 2004 TDI Low MPG Issues

I recently picked up a 2004 TDI (BEW PD engine) and was a little hestitant as I've never owned a diesel before, but have always owned VW and knew these cars were pretty highly coveted so decided to give it a try.

I drove the car approx. 300 highway miles from where I purchased, and was exceedingly happy to find that even with the 5AT it made 48MPG the trip home. However, since then, I've been unable to recreate these miles; of course, I haven't done as much pure highway driving, but I've driven a combination of city / highway streets since.

It seems when I'm about town and take the local highway, I average about 33-35, which I suppose isn't terrible- the kicker is when I do my surface driving 'commute' to work and back, which only involves about 10 miles a day. Where I live the speed limit is low (15-25) and there a lot of stops, so I imagined the MPG would decrease, but its slowly been going down every fillup- the last fillup yesterday I found it only averaged 24, which just feels really low, speed / stops / short driving and all...

Anyone who can let me know if this is par for the course with the type of driving I'm doing, or if there's some things I can check? I do have a vag-com scanner and was planning to try to find a possible boost least today- I may need a doggie collar, but I'm unsure where in the MVB to find the boost pressures. Any other common critical areas that may be causing this for me?

My '04 Jetta I picked up this spring had about 250k on it, also an auto. After the first couple tanks, I was getting about 36mpg mixed city and highway driving to work and back ~10 miles each way. I ended up getting the doggie collar off Ebay and running some gray Power Service cleaner through the fuel system. I'm now getting 41mpg. I believe the boost leak was the major culprit!

With my '04 Jetta wagon I average ~37 with lots of in-town shorter trips.

On full out highway days I average 39-40. I haven't had a long enough trip to test it out with a Malone stage 1 tune with dynamic EGR. I suspect it will do better.

I have checked for boost leaks (found none), had the injectors refurb'd by DBW, and recently replaced my tandem pump. One of the first things I did when I got the car (about a year ago) was a home brew doggie collar.

I just scored and cleaned up an intake manifold, so I can change it out without having to clean it at the same time. The one I pulled had ~250k on it, it was not plugged, but it was full of nasty oily soot. I will be interested to see what if any difference it may make. Not sure when I will put it in though.

I pulled off the intake hose a little bit ago as I was checking the timing belt, and I did notice it doesn't seem to fully seal now (and pulls back a liiiittle bit under load) but didn't think it would cause this drastic of an issue- I'm appalled how much less I'm getting than you guys and the folks on reddit.

I did notice the intake hose had quite a bit of oil in it- none pooling really, but it seemed slick and was wet to the touch- so of course I've worried about a turbo going bad and all that, but since my last oil change ~2k miles, it hasn't burned or lost any oil on the dipstick.. so I'm not 100% sure its a major thing.

A little bit of oil in the intake system is fairly normal, if you're not burning much I wouldn't worry.

30-35 MPG city is normal for an automatic, if all you're doing is short drives where the car barely gets up to operating temperature and is in stop and go traffic, 25 isn't unbelievable. You can easily check how well your turbo is boosting by using the following guide malonetuning.com/assets/files/vagcom_logging_guide.pdf basically you're looking for the requested vs actual boost values to follow each other closely, and for the N75 % to compensate when needed. 0 % = fully open, 100% = closed.

Unmetered air leaking in could cause over-boosting (like at the intake pipe), anything leaking pre MAF or pre MAP will be measured, compensated for, and noticeable through logging. The clip on intake hose to manifold connection should have a little bit of slack. If it's bad, the car might smoke due to a lack of air.

Your EGR/intake might also carbon up a bit with a lot of city driving, I'd make sure to see some highway use/semi hard driving or look into running it dynamically.

In my 04, I am getting between 35-37 around town but it will push 50 mpg on the highway if I stay out of the go pedal.

Seems I'm having another issue then. I'll probably pick up a doggie collar as they're cheap and saves me having to worry about that, and check the boost after I install. Aside from that and potentially dragging brakes, any other particular problem areas I should check out first?

I've had an 05 PD 5 speed wagon with 220K and currently driving an 04 5 speed PD wagon with 370K and they averaged 41 mpg city/hwy. My auto ALH wagon gets 40 mpg, lol. Regardless, still not complaining.

mjydrafter said:

With my '04 Jetta wagon I average ~37 with lots of in-town shorter trips.

On full out highway days I average 39-40. I haven't had a long enough trip to test it out with a Malone stage 1 tune with dynamic EGR. I suspect it will do better.

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I am very close to getting a Malone Stage 1 & Dynamic EGR tune on my 06 PD Golf, so I would be very interested to hear your results! THanks in advance.

-Vince

Schaefer.vince said:

I am very close to getting a Malone Stage 1 & Dynamic EGR tune on my 06 PD Golf, so I would be very interested to hear your results! THanks in advance.
-Vince

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I have the EGR turned off, stage 1 by Celtic, no kitty and Aeroturbine muffler and got 41 on a recent trip fully loaded with passengers and gear, through some very steep mountains and 30+ deg C temp.

My bone stock 05 PD wagon got 41 but it only had 220K, this car has 370K. My old 05 had tons of power bone stock.

turbovan+tdi said:

I have the EGR turned off, stage 1 by Celtic, no kitty and Aeroturbine muffler and got 41 on a recent trip fully loaded with passengers and gear, through some very steep mountains and 30+ deg C temp.
My bone stock 05 PD wagon got 41 but it only had 220K, this car has 370K. My old 05 had tons of power bone stock.

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Good to know, thank you! Is that with an auto or manual? I am fairly sure I don't want to delete the EGR entirely, as Maine's winters can make the warm up take long enough already. Putting in a frostheater this fall, in an effort to reach operating temp that much quicker.

I recently applied a Malone Stage 1.5 tune with Dynamic Idle/EGR on my BEW powered Jetta...

I think I am now on my 4th tankful since the uprade and have noticed no significant change in fuel economy.

+1 on engine not getting up to temp.

When I noticed my thermostat was only keeping the temp at 170 I was getting 39-40 mixed/ 45 Hwy. After replacement and holding 190 I would get 40-42 mixed and on a road trip the Las Vegas I was averaging 47. This was while driving 5-10 mph faster than I would during a "local" road trip.

Check you temp with your scanner (dashboard temp is just an idiot light with a needle). My guess is you are spending most of you commute under operating temp. And stretch her legs once in a while. Try to make Ely in 3 hours, that ought to clean some of the garbage out of the engine.

Schaefer.vince said:

Good to know, thank you! Is that with an auto or manual? I am fairly sure I don't want to delete the EGR entirely, as Maine's winters can make the warm up take long enough already. Putting in a frostheater this fall, in an effort to reach operating temp that much quicker.

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Both were 5 speeds.

EGR is still there just turned off. I have read by many that on the PD, EGR doesn't effect engine warm.

turbovan+tdi said:

Both were 5 speeds.
EGR is still there just turned off. I have read by many that on the PD, EGR doesn't effect engine warm.

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The 04 with a delete, seems to warm up faster than my ALH's, at least on the dash gauge.

fruitcakesa said:

The 04 with a delete, seems to warm up faster than my ALH's, at least on the dash gauge.

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Interesting,