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TDI Fuel Economy Discussions about increasing the fuel economy of your TDI engine. Non TDI related postings will be moved or removed.

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Old September 24th, 2018, 19:49   #1
joecitizennn
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Default Inconsistent mileage with a PD

I have an ALH and a BEW jetta. The ALH gets 44 to 45 mpg under almost all circumstances regardless of how it is driven. The PD is a wierd animal by comparison, it gets a broad range of mileage and a broad range of performance. For example, on a recent 250 mile trip via interstate, i got 58 mpg. Two weeks later i took the exact same trip and got 35mpg. My tank vent is removed and i always bump my tank off three or four times when filling to make sure it is full. Point is... always get consistent mpg with the ALH, but never with the BEW.

Then there is the other thing, sometimes this car seems to have the same power as the ALH on WOT, but often it seems to have nearly double! When it is acting peppy, it will roll a black cloud of smoke that fills the roadway and it runs like a raped ape. (very fast).

This 2005 TDI PD BEW has a new lift pump, new tandem pump, all new fluids and filters and seems to be in very good mechanical shape... but i can't seem ti figure out its random performance. Any ideas?

Edit: both cars are 5 speeds and my general driving style is to hypermile, strategic coasting and conservative throttle use.

Last edited by joecitizennn; September 24th, 2018 at 19:55.
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Old September 25th, 2018, 07:10   #2
SilverGhost
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More details on PD - has the cam been replaced? Do you ever do the "Italian tune up"? How many miles on the odo? Have checked for stored DTCs in ECM? What is the cylinder balance (MVB 23).

Jason
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Old September 25th, 2018, 11:12   #3
joecitizennn
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Italian tuneup- yes
Intake manifold recently cleaned.
No stored codes.
180k on the clock
Cam lobes all inspected and show little to no wear, they have the same amount of edge chamfer all the way around the lobe.

What do you mean by cylinder balance? I do not have vag com BTW.
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Old September 25th, 2018, 11:43   #4
andreigbs
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Edit: skipped past "new lift pump" which would have been my question.

Could an intermittent MAF signal produce random power?

You'd need VCDS to really check.
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Old September 25th, 2018, 12:09   #5
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Don't know if I have the term 100% correct, but you can read the amount ECM is adjusting the injector rates. I think the main purpose is "smooth running control" which is a nice way to say make it run smooth as a gas engine so more people don't complain about how rattly and shaky it is.

But the values are useful in finding problems. Hopefully one of the more advanced tinkerers will chime in soon. I'm a little rusty on diag with these numbers.

Sounds like something is sticking or changing drastically intermittently. The cleaning the intake statement has me worried. Did you clean the EGR valve? Between my own experience and that of tech line, cleaning that valve can cause sporadic issues. Or sometimes even total failure of the valve.

The random extra power along with loads of smoke make me think two things - either more fuel or less air. Smoke could be either, but the power makes me think extra fuel. You may have a fuel injector issue.

Jason
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Old September 25th, 2018, 12:27   #6
joecitizennn
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Well, when i first noticed wierd issues i checked the cam lobes which required egr removal. It and the intake had some accumulated soot lumps so i cleaned the intake. I removed the soot from the egr but did not use solvents or take it apart.

Cleaning the intake did not change the inconsistent mpg but i did get more power. I have not had this car long and i am wondering if someone chipped it or messed with the computer at some point.

Last edited by joecitizennn; September 25th, 2018 at 12:33.
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Old September 25th, 2018, 13:01   #7
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One other thing: the intake has those little flaps and a motor that opens up the airflow for WOT, and I've read where that motor doesn't work so the flaps stay shut restricting air.

Maybe that intake manifold flap thingy is only working sporadically.
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Old September 26th, 2018, 08:52   #8
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Quote:
Originally Posted by andreigbs View Post
One other thing: the intake has those little flaps and a motor that opens up the airflow for WOT, and I've read where that motor doesn't work so the flaps stay shut restricting air.

Maybe that intake manifold flap thingy is only working sporadically.

yes, there is an intake manifold switching valve that might be faulty. You could try taking a vacuum gauge reading at idle.
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Old September 26th, 2018, 11:06   #9
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Quote:
Originally Posted by andreigbs View Post
One other thing: the intake has those little flaps and a motor that opens up the airflow for WOT, and I've read where that motor doesn't work so the flaps stay shut restricting air.

Maybe that intake manifold flap thingy is only working sporadically.

If the flap stayed shut, it wouldn't run.

Check/replace thermostat-OE only, aftermarket are garbage, and change the green coolant sensor on the drivers side of the head.

You'll need VCDS but check torsion value as well.
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Old September 26th, 2018, 11:33   #10
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WAIT!

MkIV PD, I don't think it has the tumble flaps, but could be wrong. There is a change over flap but I think that is part of the EGR cooler and not the intake. Later CR TDI does have tumble flaps.

The other flap is the ASV or throttle body thing that will kill the engine and stop it from running if stuck shut.

I would think a crappy thermostat would be consistently bad, not vary between good and bad.

Another question I thought of - does the smoke cloud stay consistently thick, or does is slowly clear out if you accelerate hard a few times? Just wondering if the soot is building up from running mediocre, then getting blown out when it runs great.

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Old September 26th, 2018, 13:02   #11
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Quote:
Originally Posted by SilverGhost View Post

I would think a crappy thermostat would be consistently bad, not vary between good and bad.
Yeah, thermostats become irregular, you can't sometimes see the swing by the gauge, but it can and does affect MPG.
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2003 GSW, 2.0L ALH, Stage 2 Colt Cam, 1756 turbo, auto, silver, 380k-Wife's.
2004 GSW TDI, blue, 5 speed-DD-Malone stage 2, no kitty, aeroturbine muffler, PD150's.
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Old September 26th, 2018, 13:04   #12
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The other flaps are simply for making it a 2 stage intake, they are closed at idle and low rpm for more torque, opened at higher rpm. I simply unplugged the vacuum line, didn't notice any difference in power or mpg. There fail safe is open and they need vacuum to close.
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1984 6.2 Diesel Get A Way van, remote turbo setup designed/installed by me, burning anything that burns.
2003 GSW, 2.0L ALH, Stage 2 Colt Cam, 1756 turbo, auto, silver, 380k-Wife's.
2004 GSW TDI, blue, 5 speed-DD-Malone stage 2, no kitty, aeroturbine muffler, PD150's.
2003 JSW 1.8T, silver-parting out. 2006 JSW, TDI 5 speed, blue.
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Old September 26th, 2018, 14:04   #13
hajes
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looks like MAF, Lambda issue and some eExpert engine calibration

I had faulty MAF with readings -10%...of course you won't see that as OBD error.

I have PD too (VW 2.0 TDi - BMM)...always consistent with fuel...only power was different with faulty MAF
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Old September 27th, 2018, 20:46   #14
joecitizennn
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Quote:
Originally Posted by SilverGhost View Post
Another question I thought of - does the smoke cloud stay consistently thick, or does is slowly clear out if you accelerate hard a few times? Just wondering if the soot is building up from running mediocre, then getting blown out when it runs great.

Jason

It smokes when you hit the throttle and will do it every time while the car is running. The next day it may act differently. And when it smokes... it can really get with it... like at a truck pull.

I did change my engine temp sender, but i have never changed the thermostat, the temp always seems to be the same.

I cleaned the element in my maf yesterday with alchahol and took a 145 mile trip and the needle has yet to break 1/8 tank, but i won't know untill my next fill. I'm not getting my hopes up, because it has gotten good mileage before.
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Old September 28th, 2018, 12:25   #15
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Well, I'm just going to reiterate what drivbiwire has said about cleaning MAF by saying DON'T. You may get lucky and it works for while. But if it is the MAF, then I would consider replacing it.

Jason
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