Can you help troubleshoot low mileage (ALH 2003 Jetta)

I recently purchased a 2003 Jetta TDI at 225k miles (5spd manual). The engine seemed to be in great shape at purchase (no smoke, no funny noises, good power), and the service records were good. I got this car so that I could run something on B100, which I've been doing for ~ 400 miles.

In my last few tanks, I've been tracking fuel economy by taking number of miles driven over the amount pumped into the tank until the pump stops on its own (not worrying about foam or venting). I've gotten 31 and 32 mpg for the last two partial tanks, mainly city driving. This mileage includes pre/post EGR/intake manifold cleaning (it was about 60% occluded - I noticed much better power, but it seems mileage didn't change much). Tires were at 35PSI.

I understand that B100 + city driving will result in lower fuel economy, but it still seems too low for me - I get pretty good mileage on other vehicles and have experience with how to drive turbocharged engines. I picked up VCDS, and the IQ/timing are within spec at idle. The timing is slightly advanced, and the IQ is around 4-5 mg/str, with fairly equal numbers across the different injectors. The turbo doesn't seem to be acting strangely, but I don't really have a good baseline for what it should be like. I tested the MAF by unplugging it, but the car drove like crap after I did that. I'm waiting until I hit 1000 miles on B100 to change the fuel filter.

I decided to do some of the VCDS tests given at: https://sites.google.com/site/1810martin/vcds-and-pd-tdi-engine-health-check, which is to check the injection quantity, boost, and air flow at the MAF.

Under load (3rd gear, moving from 1500-4000 RPM over ~ 17 seconds without flooring it), all of these figures seem low to me, compared with the reference values given at the site. I'm not clear whether these values are within spec, or whether they are related to my fuel economy issues.
(click on images for full size)
Injection quantity:

Boost pressure:

Air mass (I think the "Actual" mass drops off at the end because I wasn't really pushing it at the upper RPMs):

Should I be looking further into why values in all of these plots seem low, or did I bungle the test? Are these related to the low fuel economy?


I should also add that my thermostat reaches 188F, and both of these mileage estimates are from right after I had alignment done (new suspension). I haven't tested for a stuck parking brake, but the car rolls in neutral on even a very slight incline, and I can push it on flat ground with one foot hanging out the door. All original trim pieces are intact. The weight of the car generally includes me, a baby + carseat + stroller, and a 50 pound pooch.

Have you inspected engine for fuel leaks? The return line between your injectors, injection pump, or fuel lines? any fuel leaks will lower your fuel economy.

Run higher tire pressure too, if that's an option with your tires. Light duty tires are safe to run 90%+ their stamped pressures on the sidewall. Most hyper miles run max pressure. Rolling resistance equals energy.

I just started running my tires at 40 PSI (90% max), so I can update after my next fill-up. I would have expected 35 PSI to be adequate for getting at least upper 30s in MPG, but maybe not?

Have you inspected engine for fuel leaks? The return line between your injectors, injection pump, or fuel lines? any fuel leaks will lower your fuel economy.

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Good call - I have the engine cover off for the summer and have been pretty intimate with the engine compartment lately, so I'm pretty sure I would have noticed anything visible after opening the hood. I'll add that to my list of things to double check.

I would definitely look into making sure you dont have any brakes dragging.

There is a sticky for that, go through it.

http://forums.tdiclub.com/showthread.php?t=342274

You should be in the mid to upper 40's unless your sitting in traffic for hours.

Tdijarhead said:

There is a sticky for that, go through it.

http://forums.tdiclub.com/showthread.php?t=342274

You should be in the mid to upper 40's unless your sitting in traffic for hours.

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Thanks - I have seen that thread and gone through the list, which is why I opened this thread.

I upped my economy to 33mpg with tire pressure increased to 90% max. I also decided to replace my fuel filter early to see if that would help, and I got a gallon and a half at 34.5 mpg, but that was based on one highway trip, so I'm not sure it really helped.

As far as the other items on that list: the car was recently aligned because I replaced the front shocks; I've checked the timing on VCDS, and I'm slightly advanced but in spec; I tried an MAF cleaning + testing MAF by temporary delete, and it seems my MAF is in working order; I cleaned my EGR and intake manifold; my parking brake does not appear to be stuck (no excess brake dust on either rear wheel, easy to push car on level ground); I'm not having any discernible bad turbo symptoms; I'm also a relatively conservative driver and keep my foot off the brake as much as possible.

My next idea is to replace all vacuum lines, since some of them seem a bit worn. I've also had some recent glow plug failures (which might point to injectors???), but I think I can chalk that up to trying to save too much money on them. I've got some better ones in shipment from KermaTDI.

I'm really at a loss, otherwise, and hoping that some of the VCDS logs I posted would point to something I can't see, or maybe someone could point me to other things to try. Other than the low economy, the car drives really, really well. The economy seems so low, I feel I must be missing one big thing rather than a bunch of small things that I've already tried.

I agree your mileage is low. You seem to have tried a bunch of things. Let me reiterate what was said above, make darn sure your brakes are not dragging. I had a dragging problem and I didn't realize it because the car rolled easily. Having got that out of the way.

Where exactly is your IQ set and what is the number that your timing is set on the graph?

Vacuum lines are a good idea. Glow plugs won't make any difference except for starting, and even then only when the temps drop.

I put the rear up on jackstands, and it does look like one (if not both) wheels have some drag. I have symptoms of a warped rotor (shaking during braking at speed), and one of the wheels has a spot where it comes to a stop while trying to spin it. I guess I'll replace the pads and rotors while checking out the calipers. My "this month" job just turned into my "today" job.

I'll update with the VCDS figures and new fuel economy once I get that done. Fingers crossed!

EDIT: oops... not today. Need to order some grease.

Just to update this for future reference:

After my last fill-up, I inspected my brakes. The pads don't appear to be wearing excessively or unevenly. The parking brake does not show any signs of sticking. When I had the wheels on and the rear jacked up, I tested the brake drag by trying to manually spin the wheels with a good, hard push. I got 2-3 revolutions per hard push on rear side driver wheel and about 1 revolution per push on the passenger side. The fronts got about 1 rev each, but I'm not sure if the fronts are supposed to be a bit different. I've still got some miles in the pads, so I'll just change them on schedule and change the rotors when I do - the rear rotors both are uneven and the fronts are pretty worn. I checked the caliper slide pins, and they all seemed a little sticky - slide pin boots looked good. The caliper piston boots appeared dry, but still intact. Getting the caliper pistons to retract took a bit of effort with a caliper tool.

After futzing around, I did a complete flush and pressure bleed of my brake lines. The old fluid was green and fairly dark with a few little flakes of rust. I also greased all of the slide pins with Permatex purple brake parts lube. They seemed to move more freely after that. The feel at the brake pedal improved a bit after the flush, but it wasn't noticeably bad to begin with.

At my last partial fillup, I recorded 31 mpg, so the flush + caliper pin lube did not appear to solve the problem.

Given the difficulty I had in getting the pistons to retract, my next thought is to replace the boots + seals with the idparts seal kits. My next thought after that is to replace the brake lines going into the calipers, but I don't want to that without ruling out the piston seals. Any other thoughts are appreciated.

EDIT:
I forgot to put my IQ/timing results up. So, before I started this post originally, I had used the hammer mod to get IQ to 5.0 mg/str. I re-checked it just now, and, at idle and with engine warmed up (coolant temp = 91C), I measured an IQ of 2.4 mg/str!

Timing was: 0.4 BTDC specified, 2.0 BTDC actual, which is advanced but within spec.

Obviously, IQ was too low (too high?), which should impact fuel economy. I got it back above 3 mg/str with VCDS adaptation, but I guess I'm getting the hammer out again this weekend. The only thing I can think is that I may have had the A/C on when doing it last time (my dog likes to sit in the car while I work on it - didn't want to cook him!).

When you check and adjust the IQ or timing make sure the engine is warm. 190 is the operating temperature. It does sound like your brakes may have had a little drag, it sounds like you have solved that by taking care of the pins. Did you try turning the tires after addressing the slider pins?

IQ set between 4.5-5 is generally regarded as good for fuel mileage. Lower, 1-3 for more power.

Where is your timing on the graph?
http://www.ross-tech.com/vag-scope/TDIGraph.html

Tdijarhead said:

Did you try turning the tires after addressing the slider pins?

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Nope - ran out of time to do that. I'll do it next time I've got the wheels up.

Tdijarhead said:

Where is your timing on the graph?
http://www.ross-tech.com/vag-scope/TDIGraph.html

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Here's my version of the graph. Timing at 63. Sorry - I didn't realize that had a different axis from the value reported in degrees.



EDIT:
I think I selected the wrong engine on the graph, but the graph on your link has the correct one. On that graph, the timing would still be within spec, but advanced.

I just went out to the garage to check how freely I could spin my wheels (backed in, set parking brake and then released). I jacked up one at a time (so a little different from the first time I checked, with rear/front up on my 2 jackstands). Rear left = 1 spin with a fairly good push (not enough to rap my knuckles on the fender); rear right = 2.5 spins. Both fronts got about 1 spin each in neutral.

Qualitatively, the wheels felt freer than the last time I did this, but I'm guessing they still don't spin as freely as they could.

One thing I have seen is that if all the wheels have dragging pads, that you should suspect a problem with the master cylinder. I've also heard that it's a pretty rare problem. Given the condition of the caliper boots, I think I'll stick with my plan to lube and replace the seals on the caliper before suspecting other things.

I very much appreciate all of the help tracking down my fuel economy issues!

For comparison, I put our mk6 Golf on the jack to test the wheel spin. For the fronts, in neutral, I was getting about 2 revolutions per solid push by hand. In the rear, I stopped counting after 4 revolutions, and it kept going for maybe 10 revolutions or so. I could also hear the pads rub on high spots on the rotor in the rear, but it was still MUCH freer than the mk4 Jetta wheels. I'm not getting any wheel bearing noise, so I still suspect the brakes. Is there anything else that would affect how freely the wheels spin (especially rears) that isn't brake or bearing related?

When I had the calipers off for inspection, I was able to spin the hubs pretty easily by hand, so I'm still fairly sure it's the brakes dragging.

EDIT: for more details, I set the IQ to 5.8 mg/str with the hammer mod (after resetting the adaptation value to the default), this time being sure to have the A/C off. With the A/C on, it jumps to about 10.0 mg/str. For fun, I did 2 0-60 tests with VCDS and got a best time of 11.3 +/- 0.7 seconds. I'm not exactly a track driver, so I suspect this could be improved. I didn't notice a qualitative drop in power after adjusting the IQ, but the engine quieted down a good bit. At this point, I'm just looking for excuses to drive so that I can re-check the fuel economy.

After you address the brake issues my next step would be to get the IP timing closest to the "dead-on" timing spec as you can which is 46 degrees. You are nearly 20 degrees advanced right now.

Update: just put in 70 miles at 41.9 MPG at the new IQ value, which is my first 40+ partial fill-up. I used regular D2, so the tank is probably between B80 and B90. I also went through this thread: http://forums.tdiclub.com/showthread.php?t=123503.

There were a couple of things I tried from that thread that I hadn't heard elsewhere. Namely, driving with a 'heavy foot' it until you get to cruising speed and then getting into highest gear possible where you are 1350+ RPM. I would have expected speeds that low to lug the engine, but the car seems fine over flat ground at 1400 RPM. The other thing was to stop doing any engine braking at all (i.e. I'm coasting in gear down to about 1000 RPM before hitting the clutch, but not downshifting with heel-to-toe driving to slow down).

casey823 said:

After you address the brake issues my next step would be to get the IP timing closest to the "dead-on" timing spec as you can which is 46 degrees. You are nearly 20 degrees advanced right now.

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Interesting. The majority of the advice I've seen is to have the timing advanced, but in spec. I'm guessing that must be for ideal power, though. I'm due for a new TB in the next month or so, so I'll give dead-on timing a shot. Thanks!

I just solved my issue after Tbelt replacement. Mileage back to 55 on a tank. I had what I think was a stuck VNT accuator. My post is under 2003 Jetta poor mileage on MK4 forum.

It was stuck. Just one of those things. Good luck

Couleetdi said:

I just solved my issue after Tbelt replacement. Mileage back to 55 on a tank. I had what I think was a stuck VNT accuator. My post is under 2003 Jetta poor mileage on MK4 forum.

It was stuck. Just one of those things. Good luck

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Thanks. I think I've ruled out the VNT actuator - I observed it during a VCDS test, and it seemed to be moving fine. I'll check out your post, though, and I'm glad you were able to fix your issue. I'm holding out hope for the timing belt change to do it. Installing new caliper seals + boots and cleaning up the calipers didn't seem to help with mileage - last partial tank was still in the 30s.

To rule out the quality of the B100 you're using why don't you let it go real empty and fill up with a good quality D2? Then run all of that out and check mpg?

FWIW:
When did you last change the air filter?
Have you ever cleaned the snow screen?
And maybe, even though the engine runs smooth, your compression is down. Could do a compression check to verify rings and valves are sealing well.

DanEboy said:

To rule out the quality of the B100 you're using why don't you let it go real empty and fill up with a good quality D2? Then run all of that out and check mpg?

FWIW:
When did you last change the air filter?
Have you ever cleaned the snow screen?
And maybe, even though the engine runs smooth, your compression is down. Could do a compression check to verify rings and valves are sealing well.

Click to expand...

I did start out with D2 in the tank and I didn't religiously track my mileage, but there wasn't much of a difference. I think my first tank with the car was in the 30s, mileage-wise. I didn't pay much attention because I was doing so much to the car as it was.

Last air filter change was with my last oil change, which started right before (or early on?) in this thread. Snow screen was cleaned at the same time (it wasn't actually that bad, but it was dirty).

I have not done a compression check! I need to figure out how to do that. Autozone doesn't seem to have the right tool (their compression tester is for gassers). I haven't been super motivated to do this because my impression was that if the MPG was down to compression issues, that I would see other problems (smoke, oil consumption). I don't see any other issues, however. I will move this up my list of priorities, though. I have an alignment coming up after replacing control arm bushings and outer tie rod ends, so I'll see if the shop can do a compression test at the same time. Thanks!