Steady State Boost

I'm trying to track down a fuel mileage drop on my 2004 PD Wagon 5spd. When I first bought the car, I would reliably get 42-44mpg with my mixed 70mile commute, with my average speed at 60-65 for almost the entire trip. Now, I'm lucky to get 38. I've gone through the drivetrain, replacing bearings and brakes F&R.
After installing my boost gauge, I noticed that I typically run a steady 7-8psi at 60-65mph on flat roads. Recently however, I've noticed that pressure sometimes "hangs" around 12psi, with no real clear cause. Sometimes letting off the Cruise or throttle and getting back on it will return it to 7-8, other times it goes right back to 12.
So, for those that have guages, what do you typically see at steady cruise? Any thoughts on the weird boost activity? I was thinking it may be the actuator or the vanes are starting to get sticky (car has just under 80k). One of these days I'll pull the turbo and clean it (bought it w/50k and haven't done it yet).

Thanks!
-Lloyd

I just put a boost gauge on my 03 Golf last night, and cruising on flat ground I show no boost. When I come to a hill it will start to go up.
This was on back roads, I will check tonight on my way home from work
to see what it does on the highway.

DieselCG, please do a search on "snow screen cleaning". Then find out if you have the snow screen in place. If you do, IT'S MOST LIKELY CLOGGED! Cleaning it will restore proper air flow and decrease the amount of boost necessary for a given speed. Your MPGs will come back to normal.

That was my experience, and I'm sticking to it.

could also be a vacuum line leak, or a bad maf.

puter said:

could also be a vacuum line leak, or a bad maf.

Click to expand...

So everyone is saying that I shouldn't be boosting on flat roads at 50-60mph?

I don't have a snow screen, as there is not snorkle tube leading from the airbox down to the bumper. I think there may have been a minor collision before I bought it and it fell off or was damaged.

What is the best way to check for vacuum leaks? What about diagnosing the bad MAF? The only mod I've done to the car engine wise is the boost gauge and an EGR delete.


Thanks,
Lloyd

You will get some amount of boost whenever the engine is running. The more demand on the engine, the more boost.

I personally don't think it's worth troubleshooting vacuum leaks, takes longer than it takes to just replace all the lines...and the lines will only cost you ten bucks or so.

puter said:

You will get some amount of boost whenever the engine is running. The more demand on the engine, the more boost.

I personally don't think it's worth troubleshooting vacuum leaks, takes longer than it takes to just replace all the lines...and the lines will only cost you ten bucks or so.

Click to expand...

I absolutely agree with the vacuum lines. I'll poke around tonight and tomorrow and see if I can get them all swapped out.

Besides the second poster, does anyone else have a boost gauge? I'd like to know how many psi "off" I am with steady cruising. (running 8-10psi on level ground between 60-70mph).

Thanks!
-Lloyd

For a PD that doens't sound too far off when cruising, they run more boost than previous TDIs, that intake flapper thing and more EGR seems to be why.

I forced myself to putt around at 55 to watch the boost for you. 8-12psi depending on the grade.

gforce1108 said:

I forced myself to putt around at 55 to watch the boost for you. 8-12psi depending on the grade.

Click to expand...

Thanks! I really appreciate it. That makes me feel a lot better.

Yesterday I tore into things. I checked/corrected the cam to crank timing (it was off by just a hair). I then checked the VNT actuator on the KP39. It was starting to move at just under 2in/hg and closing at 18. I adjusted it to the middle of the factory spec at 4in/hg and 19in/hg respectively. Finally, I replaced the air filter which had about 10k on it.

Overall the car seems much more responsive now, though I think it has more to do with the cam/actuator adjustments. Boost is much more stable and doesn't have the spikes to 18-19 I was getting (factory tune). It's still too early to tell what the effects will be on economy. I'll post up after a I run a full tank and let everyone know.

Thanks for all the great help and advice!

-Lloyd

Changing the air filter with only 10K miles?

2004 TDI maintenance schedule:
http://www.vw.com/dealer/Maintenanc...TEMPLATENAME=maintenanceComplete&output=print

I've got a PD and at 50-60 mph on the highway (flat) I se between 3-5 psi. This is similar to the boost I had seen on my Mk 4 in the past. As soon as I let my foot off I see 0 boost then it goes right back up when I give it a little tip in. 8-12 psi at the same speed is higher that anything I've seen.

Bob_Fout said:

Changing the air filter with only 10K miles?

2004 TDI maintenance schedule:
http://www.vw.com/dealer/Maintenanc...TEMPLATENAME=maintenanceComplete&output=print

Click to expand...

Just trying to rule out everything. Besides, it was an autozone special and I had a spare MANN laying around.

If this is higher than normal boost, does anyone have any other ideas? The only thing I can think of is that there is some driveline drag I'm not considering. I've replaced brakes, rotors and bearings at all four corners. I've drained and replaced the manual tranny fluid with the latest VW spec.

ThoughtS?

I fixed a whole lot of little boost leaks by replacing all the orings from the turbo to the intake manifold. I used larger ones (napa 1108)for all but the smaller two near the turbo - those I bought new from VW.

I still show boost even when coasting in gear. Somewhere around 3-4psi coasting at 60mph.

gforce1108 said:

I fixed a whole lot of little boost leaks by replacing all the orings from the turbo to the intake manifold. I used larger ones (napa 1108)for all but the smaller two near the turbo - those I bought new from VW.

I still show boost even when coasting in gear. Somewhere around 3-4psi coasting at 60mph.

Click to expand...

I've replaced all but the two smaller ones you mentioned. Do you happen to have the part number for those?

Thanks!
-Lloyd

Pull that EGR valve and make sure it moves freely and closes tight.

LessIsMore said:

Pull that EGR valve and make sure it moves freely and closes tight.

Click to expand...

I've got the EGR blocked off at the turbo outlet and at the upper intake pipe. Should I still pull it?

Thanks!

DieselCG said:

I've got the EGR blocked off at the turbo outlet and at the upper intake pipe. Should I still pull it?

Thanks!

Click to expand...

Somehow I got the impression that we were talking about a stock BEW setup, and a hanging EGR is detrimental to MPG and performance in that case. But no, your EGR is now doing nothing but plug holes in the IM, which I'm sure you know perfectly well.

DieselCG said:

I've replaced all but the two smaller ones you mentioned. Do you happen to have the part number for those?

Thanks!
-Lloyd

Click to expand...

I don't think I have the number anymore. I took a trip into the dealer to find them. They have a weird description so don't be surprised by the listing the dealer might have.

DieselCG

I just found this thread. My 2004 Golf has boost numbers like your's, but no drop in mileage, still getting 42-46 MPG.

Did you ever find anything to correct?

DieselCG said:

Just trying to rule out everything. Besides, it was an autozone special and I had a spare MANN laying around.

If this is higher than normal boost, does anyone have any other ideas? The only thing I can think of is that there is some driveline drag I'm not considering. I've replaced brakes, rotors and bearings at all four corners. I've drained and replaced the manual tranny fluid with the latest VW spec.

ThoughtS?

Click to expand...

Just tried "CRC" "Mass Air Flow Sensor Cleaner" and car runs 2-3 PSI less at 65 MPH. So maybe, more cleaning or time for a new MAF. There are no codes.
http://www.crcindustries.com/files/19965_1.PDF

http://www.crcindustries.com/auto/content/prod_detail.aspx?PN=05110&S=N