Inconsistent mileage with a PD

joecitizennn

Active member
Joined
Oct 26, 2014
Location
arizona
TDI
jetta
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.
 
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SilverGhost

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Mar 25, 2005
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Back in So Flo - St Lucie
TDI
'05 Golf - totaled :(, wife's '13 Beetle - buy back, TDIless
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
 

joecitizennn

Active member
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Oct 26, 2014
Location
arizona
TDI
jetta
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.
 

andreigbs

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Joined
Sep 27, 2004
Location
Walworth Co., Wisconsin
TDI
N/A
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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SilverGhost

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'05 Golf - totaled :(, wife's '13 Beetle - buy back, TDIless
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
 

joecitizennn

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Oct 26, 2014
Location
arizona
TDI
jetta
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.
 
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andreigbs

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Location
Walworth Co., Wisconsin
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N/A
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.
 

turbotorq

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Joined
Feb 1, 2013
Location
Kingston, ON
TDI
04 Jetta TDI
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.
 

turbovan+tdi

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Mar 23, 2014
Location
Abbotsford, BC.
TDI
2003 TDI 2.0L ALH, auto, silver wagon, lowered, Colt stage 2 cam, ported head,205 injectors, 1756 turbo, Malone 2.0, 3" exhaust, 18" BBS RC GLI rims. 2004 blue GSW TDI, 5 speed, lowered, GLI BBS wheels painted black, Malone stage 2, Aerotur
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.
 

SilverGhost

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Mar 25, 2005
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Back in So Flo - St Lucie
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'05 Golf - totaled :(, wife's '13 Beetle - buy back, TDIless
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.

Jason
 

turbovan+tdi

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Mar 23, 2014
Location
Abbotsford, BC.
TDI
2003 TDI 2.0L ALH, auto, silver wagon, lowered, Colt stage 2 cam, ported head,205 injectors, 1756 turbo, Malone 2.0, 3" exhaust, 18" BBS RC GLI rims. 2004 blue GSW TDI, 5 speed, lowered, GLI BBS wheels painted black, Malone stage 2, Aerotur
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.
 

turbovan+tdi

Top Post Dawg
Joined
Mar 23, 2014
Location
Abbotsford, BC.
TDI
2003 TDI 2.0L ALH, auto, silver wagon, lowered, Colt stage 2 cam, ported head,205 injectors, 1756 turbo, Malone 2.0, 3" exhaust, 18" BBS RC GLI rims. 2004 blue GSW TDI, 5 speed, lowered, GLI BBS wheels painted black, Malone stage 2, Aerotur
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.
 

hajes

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Jan 16, 2017
Location
Earth
TDI
Skoda "Hilda" Octavia HR I
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
 

joecitizennn

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Oct 26, 2014
Location
arizona
TDI
jetta
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.
 

SilverGhost

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Joined
Mar 25, 2005
Location
Back in So Flo - St Lucie
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'05 Golf - totaled :(, wife's '13 Beetle - buy back, TDIless
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
 

joecitizennn

Active member
Joined
Oct 26, 2014
Location
arizona
TDI
jetta
Well this last tank was 52mpg wich is good, but like i said it's inconsistent and tank before last was 35. I have noticed low temperature nailing after startup and i wonder if i need to clean my injectors. What is the best way to do this on a pd?
 

andreigbs

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Sep 27, 2004
Location
Walworth Co., Wisconsin
TDI
N/A
Lubro-Moly Diesel Purge. Run it straight from the can and have the return line in the can as well (closed loop).

There are a couple how-to's around here somewhere.
 

IndigoBlueWagon

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Aug 16, 2004
Location
South of Boston
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'97 Passat, '99.5 Golf, '02 Jetta Wagon, '15 GSW
First, the only sure-fire way to get a consistent fill on a MKIV is to take out the tank vent and always fill the tank until you see clear fuel in the filler neck. It can take a little time, especially at some stations where fuel foams a lot, but any other way you do it is going to allow inconsistent FE numbers.

Second, I'm betting your low power sometimes and lots of power other times is a worn/faulty turbo actuator or poor connections between the actuator and the car harness. Both are common on BEWs as they age. You're probably getting some overboost sometimes, and full actual boost (or less) at other times.

Finally, I rotary pump TDIs seem to deliver more consistent FE than later cars. My Wagon gets 46 MPG pretty much like clockwork in normal driving, summer or winter, A/C or no, traffic or not. It'll push to 50 or more on trips, but otherwise it's pretty much always the same. PDs and CRs don't seem to be like that.
 
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