Nozzles, Timing, and other possible issues causing "poor" mileage?

Hi, I recently bought an "03 TDI Jetta (sedan) manual, and did quite a bit of work to it prior to even driving it. It has 223,000 miles on it. I replaced the timing belt, water pump, tensioner, etc. and timed with VCDS.

First off, I have always wanted a TDI and it makes sense because I commute 70 miles round trip 5 days a week plus other longer trips. I also have owned to other 2001 gassers. Anyway, my whole purpose for getting this car is to get good mileage (>45).

Things I have done to it

1. timing belt change
2. ventectomy
3. oil change with filter
4. cleaned EGR and intake manifold
5. and many other things that do not pertain to mileage

So, back to the timing, I have read many conflicting opinions about where it is best to set the injection timing to get best mileage. Some say it doesnt matter as long as it is in the range given on the graph because the computer can adjust it to where it needs to when its within those limits. Others say that they put it as advanced, within the limits, as possible, because thats best for mileage, while still others claim that (like the first opinion) it doesnt matter where the timing is at, but you should make sure that the start of injection parameters can be met. Right now I have mine set at about the midpoint. However, after several fillups, I am consistently getting 37-38. I am wondering if where I have this set could make an impact on my mileage. I should add that the engine is running great and has no modifications.

Additionally, I believe that the injector nozzles are original. I ran a can of diesel purge directly through the nozzles to see if cleaning them would help, but it hasnt. I have been considering getting the Bosio DLC520s, for increased mileage anyway. Could it be possible that the original nozzles are worn enough to decrease mileage.

Also, the previous owner said that the fuel filter had been changed in the past year, so I havent chagned mine yet, but I just bought one and plan to change it soon, so that won't be a factor.

I have confirmed that the brakes are not dragging.
If you have any suggestions are response to my questions, any help would be appreciated. Thanks.

How fast are you driving and what are traffic and other situations like? Performance and starting ok? Tires and tire pressure?
I always ran the static timing advanced and then adapted in some more, but the last few years post last TB change, I left the static in the middle. Averaging 52-55 almost every tank in non-freezing temps.
Some people will never get good mileage regardless of the vehicle setup. Others will get great mileage out of the same vehicle.
What 2001 gas VW and what average mileage did you get with that?

im driving part 75 mph highway(50%), 50% city. It starts up great every time and has good performance. It has low profile aluminum rims on it, with 50psi in every tire. I also have been trying to drive fairly easy on it. I have a 2001 vw jetta 1.8t and got around 28 average with it city/highway.
So are you saying that some cars just get better mileage than others...aka I might have a lemon?

I misread your post, I do not think my low mileage is due to my driving style, currently I am driving nice and easy (more than usual) trying to get good mileage. I have heard a lot of people say that they cannot get much less than 45 even if they tried.

Also, how much would a misaligned front decrease mileage? I might check that closer.

The wide low profile tires won't help. Must be a harsh ride with 50 psi, but if you can live with that, it helps some.
If you averaged 28 mpg with the 1.8 driving about the same routes and speeds I would expect the TDI to be better than what you are currently getting, but doubt you will achieve 45ish mpg driving 50% 75 mph and 50% "city".
I recommend a ScanGauge. It helps show relative real time current, daily and tank averages in addition to several data references that are helpful. Plus you can clear codes on the fly.

I have dash command on my Android with an elm obd adapter which does exactly that and have been using it daily to watch my instantaneous and average.

n_spot said:

If you have any suggestions are response to my questions, any help would be appreciated. Thanks.

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What size are these low profile tires and rims? Have you checked your odometer accuracy with GPS? 37-38mpg seems pretty low for a 5spd ALH car to me.

Who changed the timing belt? Is the base timing correct?
How is the coolant temp? (The actual temp, not the gauge on the dash).
Are you running A/C?

I haven't studied the topic in a while, but I thought the general consensus on here for best MPG was that the timing should be advanced to the top of the graph, and/or adapted with extra advance.

I installed a set of the DLC520 nozzles in my 03 Golf and saw no improvement in MPG. I don't regret buying them really...they did give the car a bit more oomph, which was nice, but I didn't get the MPG improvement I was after.
I know they are advertised as improving fuel efficiency by 4-6 MPG, but I don't know where the scale starts. If you're only getting 37-38mpg, you may see a 4-6mpg improvement...I'm not sure. I was already getting 50mpg, so I didn't see those increases.

My ALH 5spd Beetle has been consistently getting 49-50mpg, and my '03 Golf was hitting 50-51 with 15" tires. When I swapped a set of 17's on my Golf, the MPG dropped to 48. That's mostly all hwy, and usually at 65mph+/-. I've been running the Beetle a little faster lately...just over 70mph indicated, so likely in the high 60's somewhere...67-68.

I would think a 5spd ALH Jetta should be in the 40's for MPG at least, if not 50. That's with 15" rubber at the speed limit. If you add more speed, A/C, larger tires, etc...every one of those will decrease your MPG in increments.

I have been running 225/65 R17 tires, and I did the timing belt, but I have done 2 others in the past no problem and I checked everything many times. For the mileage I have been describing it has included about 70% AC and the static timing was dead on the center line (i.e. not advanced or retarded). My actual coolant temp runs about 200*F. Yesterday, I increased the timing to about 3/4 the way up to the top line to see if I get any improvements. By the middle of this week I will have new stock tires (firestone champion fuel fighters) back on with a front end alignment. After all these factors taken into account and driving with much less use of AC, we will see how the mileage changes. Thanks for all the continued input!

Just one possible factor... the tires you're currently running offset your actual speed by 14% as compared to stock 17s... which also affects your mileage calculations the same way. Have you adjusted your math accordingly?

Factory 17s are 225/45R17... plug that and your current 225/65R17 in here:

https://tiresize.com/speedometer-calibration/

and you'll see what I am referring to.

n_spot said:

It has low profile aluminum rims on it, with 50psi in every tire. I also have been trying to drive fairly easy on it.

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A sure way to end up in the ditch.


Manufacturers spend years researching what tyre pressures to use on a car.


At those pressures, you will reduce your tyre's footprint on the road surface and the result in the wet... well, lets just say its not favorable.

FF


Best advice? Take 10 psi out on all four as soon as you get the chance.

n_spot said:

im driving part 75 mph highway(50%), 50% city.

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I suspect that's the issue. Mileage falls off pretty fast when you get to high speeds. Most report optimal mileage around 60mph +/- a bit. And everyone knows that city driving kills mileage.
I used to have an 80-mile round trip commute and could get ~ 55mpg easily on the commute, by going ~60mph. But the ~10% city driving I also had dropped my average mileage to upper 40s.
Now that my commute is shorter and I do ~50% city driving, average mileage is around 40mph.
Those who say they couldn't get less than 50mpg if they tried are exaggerating.

Sorry guys, my tires are 225/45/R17s, not 225/65s, my mistake.

Does the IQ value significantly effect mileage? I currently have mine adapted to about 3.5 mg/stroke. Would a higher value (less fuel) make a significant difference? What do you guys have yours set at? Thanks.

n_spot said:

Does the IQ value significantly effect mileage? I currently have mine adapted to about 3.5 mg/stroke. Would a higher value (less fuel) make a significant difference? What do you guys have yours set at? Thanks.

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I have mine set at 3.2 in both cars. I've tested various IQ settings on my '03 Golf and never did see a noticeable difference in MPG. I tried it as high as 6.0 or 6.2 and didn't see any changes. I think there are some people on here that did see improvements with adjustments, but I did not.