05 passat fuel economy mystery

twfarms

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ml washington
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05 passat wagon 06 bug
I bought this 05 passat Wagon about 2 years ago and enjoy the car but from the day I bought it the fuel economy has been less than thought. The day I got it it got about 32 overall and it has steadily gone down over the 2 years to now 27ish. The previous owner (after I tracked him down since I bought from dealer) was surprised and said he got on the average all the time 36 from this car. 40 - 44 on freeway and 32ish in the city. I have NEVER seen anything over 34 even on a freeway trip for 4 hours each way. The car has always been a little I feel sluggish compared on the foot compared to the bug.

I have had this car into 5 different shops over the 2 years looking for it. They have checked everything from Maf, to fuel pump, to n75, to resistence of pump in tank, to boost leaks, fuel filters, air filters, snow screen and even the throttle position sensor. And the WHOLE time no codes except the n75 which has been replaced twice (once because of code) and another by me because of just trying something.

One mechanic said maybe the injectors are plugging but took it with a grain of salt because all the fuel "tests" came back within spec. (And he was quoting like 700 bucks an injector * 4) So didn't do anything with that idea.

SOOO fast forward to now: Fuel economy is around 26 - 27 after slowly declining over the 2 years.. All tests are normal and within spec. BUT on a cold morning startup after you have started it JUST FINE it sits there and idles just fine BUT you try to accelerate and it's barely moves UNTIL 10 to 20 seconds and then it just "comes back" and motor kicks in and off you go. Try to accelerate to hard to early for to long and it goes into limp mode (probably for lack of boost is my guess) and then restart it and usually works fine by that time and off you go..

OH and the whole time NO CHECK Engine LIghts.. no codes no nothing!! Only thing I can think of is something is telling the computer that the engine isn't ready or something????

I've been researching the Anti shutter valve and not even sure how to check that or even much about it. *SIGH* Would it not send a code if it was restricting airflow??

Any thoughts would be GREATly appreciated and fixing it would i'd be estatic!

Stumped in the Evergreen State..
 

Drivbiwire

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2013 Passat TDI, Newmar Ventana 8.3L ISC 3945, 2016 E250 BT, 2000 Jetta TDI
Assuming all other factors have been eliminated (Coolant temp sensor, fuel temp sensor, MAF, Correct Torsion value range)

As the injectors age the fuel flow (rate of delivery) drops (slows) and this gradually kills your fuel economy.

The solution is updating the nozzles and restoring the flow, this typically nets a 4-6 mpg bump using the DLC 800 compared to a new OEM injector.

The faster flow of the DLC 800 allows more efficient combustion by allowing more time for the fuel to burn. Another advantage is lower EGT's and less stress on the turbo.
 
Last edited:

twfarms

Active member
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ml washington
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05 passat wagon 06 bug
Interesting

I've thought of popping the injectors and looking at them but I know my expertise and tools aren't there. I'm not sure if they screw in or seat into a cup. And that area is to expensive to mess around with. And then that last shop said I was going to be into them for about 800 bucks per injector and i'm like umm mthat's a lot of fuel.

BUT running it through my brain over and over what this car is doing. Injectors wouldn't be the cause. If injectors are going down. Why does that car start JUST fine (1 or 2 cranks) and then idles fine but you press the throttle pedal and no response UNTIL (like clock work) 10 to 20 seconds (never counted exactly to be honest) and then the motor comes to live and off we go.. I've thought fuel leaks (nothing noticable) and if I had a fuel leak where's it going to?? back into the tank because nothing on the ground.

But a guy checked the resistence of the pump in the tank and said it was fine. (same guy who said injectors) He did replace I think the fuel pump on the engine. No help with power or lag or fuel economy.

Like I said i'm stumped.. Other than at the dealership I bought it from they put on a new timing belt and water pump when I bought it back when but all the shops have said it's probably not the problem because no codes and I guess the timing is ok from what they see..

lol Like I said i'm stumped other than if it has something to do with Temp sensor somewhere that is telling the car that it needs to warm up or something. But temp gauge works fine on console and yeah..

HELP!! lol
 

whitedog

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2004 Jetta that I fill by myself
About that temp sensor... There are two signals from that sensor. One goes tot he gauge, one goes to the ECU so the gauge may read correctly but the ECU can still think that it's cold.

So you had the timing belt put on just after you bought it. Read up on Torsion value here. They may not have set the cam correctly, but that doesn't account for the hesitation nor the slow descent in fuel economy. I would expect it to be low and stay low.
 

twfarms

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Location
ml washington
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05 passat wagon 06 bug
temp

I've wondered about them for a while and i've heard there are two but then someone said they both goto the ecu and the ecu sends the signal to the gauge on the dash. I think they said one was on the radiator (somewhere) and one was on the block (somewhere)

Anyone know about the valve/sensor bolted onto the intake manifold?? I'm thinking it might be the ASV and it might be stuck partly closed or not open all the way?? Someone has said something about an Aora or Aorta valve that acts like a choke system?? Is that and the ASV the same thing? I just can't help but think something is not letting proper boost get into that engine. either the computer telling it OR something physically BUT the boost pressure on the Vag com TEsts showed proper boosts. A little slow to go up and a little slow to come down but i've read here that is "normal" so i'm thinking it's got (if it's a boost) to be something not letting the boost in (or out)

But i'm open to anything
 

whitedog

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2004 Jetta that I fill by myself
The wiring diagram I just looked at shows pins 1 and 2 going to the instrument cluster and pins 3 and 4 going to the ECU, telling me that they are in the same sensor housing.

HERE is a link to information on the EGR and ASV.
 

twfarms

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ml washington
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05 passat wagon 06 bug
cam

my brother had a problem with a powerstroke. He switched out the cam sensor.. it would run bad and sound like a jake brake I guess.. no codes or anything since the sensor thought the cam was somewhere it wasn't..

Does this 05 passat have a cam sensor?? And chances it would be out?? My brother says to replace the MAF and see if that fixes it or the cam sensor. Right now i'm at the point of just throwing parts at it because it's not throwing a code and most of the mechs hook up to the computer and if that computer doesn't say which part to replace they are lost and just tell you it's because the right front tire is over inflated and therefore putting the sensor on the rear left out of balance so it just confuses the Ecu..:rolleyes:

I just don't know which parts.. I did unplug the MAF because he said to and it drove exactly the same on a 10 mile test drive. AND no CEL the whole time until I came home and thought about a test I read about here and put it above 4500 rpm and then it kicked the Cel on..

But Cel is another 130 bucks.. Whatcha guys think and why..

thanks
 

twfarms

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05 passat wagon 06 bug
Maf

But then I took it to the shop to have them reset it and they tested it with it plugged in (like a dummy I didn't tell them to test it unplugged) and he said it was reading just like it was suppose to within spec.
 

vwztips

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Recommend you replace the temp sensor as it is cheap (not so easy to get to though).
Next check torsion. If it is positive, I suggest going to 0.0 to -0.5
Next check your EGR valve duty cycle and pull it out and inspect too.
One last thing I can think is possibly the variable vane mechanism on the turbo is sticking, especially when cold. Could have a lot of carbon build up. You probably would not get a code if it sticks.
 

twfarms

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ml washington
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05 passat wagon 06 bug
thinking

I've pulled the Egr valve out and inspected.. it had some soot but nothing bad but I scrapped it and put it back in. I just went to the local shop (not a tdi specialist but he's got a vag com) and we checked the MAF, the temp sensor going to the computer, and even the fuel intake sensor (eventhough i'm not even sure why we need that or where it would be because it was HOT @ 80C or something so I figured it must be before the filter) And we checked the boost sensor to see if low or high boost.

The only thing that seems "common" is that the in most shops the n75 valve keeps throwing a code. It's been replaced TWICE though and there is nothing to it.. just vac in and vac out. I've checked the vacuum lines and can't find a leak. I've thought just replace and see BUT on this car I only see 3 vacuum lines.. Intake box to n75, n75 to turbo, n75 to fuel pump and i'm assuming vacuum pump with a T to go into the cabin. I've unplugged the vac tank after car has sat it "spat" at me so I think there's vacuum holding somewhere..

I haven't messed with the Variable Vane on the turbo because I just know truck diesels and they don't have that. Turbo OFF or ON!! And i'm not sure how that turbo Vane mechicsm works. Because turbo is run from exhaust and sucking in air. pure and simple.. what do the vanes do other than as a "safety" if you get overboost (ie wastegate or turbo blow off) so it doesn't blow up something??
 

vwztips

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Nice write up. The vane doesn't move much but could have carbon build up keeping it from moving freely. This could be why you think the N75 is bad as it would show the same symptoms
 

vwztips

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Nice write up. The vane doesn't move much but could have carbon build up keeping it from moving freely. This could be why you think the N75 is bad as it would show the same symptoms
 

twfarms

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ml washington
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05 passat wagon 06 bug
Rrr

my brain is working on this one..Thanks for that link.. Very informative. Also explains why those vacuums (kind of a stupid idea to put something so important relying on a 10 cents per foot vacuum line) are so important.. Also why that actuator is so important. think i'll try in the morning to try to manually activate that actuator and see if it moves of is frozen. Is there a "test" to run to see if those vanes are stuck?? And removing that turbo to clean it might be a pretty long job huh? And then clean it with???

What about the actuator though.. I've read it can go bad also or get stuck.. I see now about the tests they are talking about..Does that just screw in and out then?? I wonder about taking it off just to test it. But test is what I think the next test..

I wonder now (can any mech verify) if that is why on the last test the turbo was slower to come up to "optimal spec" and then again when foot off it didn't just "drop" rapidly and was slow to come off boost??

My head is a thinking now. I'm thinking it might be in that system anyway.. either the vac lines, actual actuator, or the vanes are sticky..

Think i'll start with the vacuum lines though and look into the actuator itself instead of tearing into the turbo just to find a broke vac line when putting it back togethor.. hehe
 

whitedog

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Location
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2004 Jetta that I fill by myself
Be methodical and test everything starting at the actuator. You should be able to move the lever by hand, though it will be stiff. You best friend is a Mityvac, hand vacuum pump. You can test the actuator to be sure that it moves at the right point, stops at the right point and moves smoothly. If all is good there, start working your way backward to the vacuum pump, moving the Mityvac to different hoses.

If you only use the Mityvac rarely, just get the cheap, plastic one, but if you want a more reliable tool, there is a more durable metal one.
 

twfarms

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ml washington
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05 passat wagon 06 bug
vac

probably pick one up in the morning and test that actuator.. I'll have to re-read what it's suppose to run at. I was reading about it's suppose to cycle full on and off with the key I think. I'll play around with it. i'm going to laugh if it's that 1 foot of hose from the valve to the actuator though..

ALL I know it's something.. My wal mart guarantee there ..

I "tested" the vacuum lines by just blowing in them on one end and putting my finger on the other and it plugged but obviously can't get my fat head to test that actuator line.

IS there a vacuum line that is better to use that is readily available? And what readily size would be best..

thanks again for all the help..
 

whitedog

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2004 Jetta that I fill by myself
There is some silicone hose that folks get from McMaster-Carr. There is a post by Paramedick that details the part numbers for the hoses.
 

oilhammer

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outside St Louis, MO
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There are just too many to list....
Did you ever check the torsion value?

What is the actual vs. requested boost?

What does the ECU see the fuel, coolant, intake air temps as?

Does the car black smoke when you take off?

Snowscreen full of crap?

Check valve on vacuum line to N75 good?
 

twfarms

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Location
ml washington
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05 passat wagon 06 bug
thanks for ?

torsion values no we didn't check that or I didn't see it if he did..

the Ecu saw the temps in C @ oh like 83 for the fuel and 90ish I think for the coolant temp and the intake air I didn't ask him about but that's a good one.

the snowscreen EVERYONE has looked @ .. lol and it's clean

And the car exhaust is great.. no black or any "smoke" white grey blue.. "except @ startup of course" And the car uses OHHH a quart of oil every 10,000..

As far as the boost it was a concern for him.. not that it was out of spec but it was slow to get into it and out of it.. meaning when he floored it.. it didn't just jump into it .. took a couple of seconds and when he just took his foot all the way off the pedal it took about the same amount of time for it to come down and he just said that was strange.

So after everyone's great comments i've decided to focus on that vane area.. I don't think i'm plugged I just think something is running right.. either the vacuum lines are plugged or broke OR that actuator isn't working properly..

I've got some help coming this morning to test that off and on test to see after sitting for a day if that actuator moves when you turn the key on.. If not I'll probably replace that actuator and all the vacuum lines..

Anybody know if that actuator screws in and out or if you can even remove it while turbo is still on the car??

thanks for everyone's thoughts and help.. I'd probably still be looking for that overinflated tire or changing fuel filters if I hadn't been gotten it.. (and yes that fuel filter is FINE.. lol )

IF anyone is in the moses lake area feel free to stop by!!:D
 

oilhammer

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outside St Louis, MO
TDI
There are just too many to list....
Did you ever check the torsion value?
What is the actual vs. requested boost?
What does the ECU see the fuel, coolant, intake air temps as?
Does the car black smoke when you take off? check
Snowscreen full of crap?check
Check valve on vacuum line to N75 good?
So you got a couple answered. Report back when you have the others.
 

whitedog

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Location
Bend, Oregon
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2004 Jetta that I fill by myself
Yes, you can move the actuator by hand while it is on the engine.

Hammer can give details on R$R since he has been shoulder deep into these things.
 

twfarms

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Location
ml washington
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05 passat wagon 06 bug
I've pretty much narrowed the search with everyone's help to the turbo actuator itself. I'm not sure without physically removing the turbo how you'd know if the vanes we stuck. At this point and time i'm pretty well out of my comfort level other than I think I could remove and replace the actuator BUT of course you can't buy it separate from VW.. Anybody know who sells a good quality replacement one? And how do you get them off the turbo.. are they screwed in or are what is the connection between the turbo vane system and that little vacuum can.. Thanks again
 

twfarms

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ml washington
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05 passat wagon 06 bug
oilhammer

I haven't been able to get back into the one guy in town who has a vw vag-com to have him recheck these numbers and get exact ones for you.

The one thing i'm curious about is you said a check valve on the vacuum line? I don't know of a actual check valve other than this little white and black round thing in the vacuum line up by the air box.. Is that a check valve you refer to??

And the actual versus the requested boost. The question I have for that is "where".. @ idle 1000 rpm.. what range?? when we went for the test drive was within spec all the time BUT it took a little bit of time couple of seconds to get there and a couple of seconds to from old spec.. took a couple of second to come down..

I do NOT want to put 900 bucks into putting a new turbo on just to replace that actuator to find out it wasn't the problem..

I can try to find out these numbers if he has time to get me back into the shop tomorrow to get the specific numbers you need..

thanks for the help
 

oilhammer

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outside St Louis, MO
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There are just too many to list....
Yes, the white/black thing is a one-way check valve. It allows vacuum to apply to the turbo side, but not bleed back off the other way. When these stick open all the time, they cause slow vacuum build in the system, and the reservoir can only hold so much.

By actual vs requested boost, I mean drive the car with the graph up and see how closely they match one another.
 

twfarms

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ml washington
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05 passat wagon 06 bug
update

Ok. I checked the vacuum lines with a mighty vac and talked to a guy at idparts.com about where the actuator might work. I found as best I could that all the lines held vacuum and the actuator worked. "only weird" thing was the guy said it should bottom out @ 15 and mine stopped moving more about 17. I t-ed into the actuator line and watched it with car running and it has about 23-24 of vacuum and when it runs that actuator it sends about 22 to the actuator and the lowest I saw was about 12 but then again I didn't ride around on the hood with my dad driving.

The actuator SEEMED to move freely with the mighty vac pumping and releasing vacuum. I checked vacuum to the n75 valve, I checked vacuum in all the lines, and started to doubt it was the turbo.

I then unplugged the maf connection and plugged it back in.. Thinking I'm going insane.

I even thought well maybe it's the fuel pump in the tank is plugged or going out or??? I researched how to "replace" that. but didn't do anything with it.

SOOOO then on Thursday I took a 2.5 hr trip with the car and it got 20 mpg down from 26 to 28.. and i'm like what the F. I didn't DO anything to the car and so I pulled into a rest area and re started the car AND tried to get into the vac lines to see if one was left off or not all the way on but couldn't because someone had taken out my phillips screw driver.. Anyway After the dinner and before I came home I borrowed one and pushed the lines on the n75 valve (they seemed tight) and then I unplugged the maf and plugged it back in. And I took off the vac line to the actuator and put it back on but it didn't seem anymore down or anything than before.. But the whole trip going to and coming back.. it ran the same.. turbo seemed to kick in but you could "hear" it running rougher and when stopped you could "smell" it.

I drove back home and got the 26 to 28.. sooo I'm just stumped other than just dropping a new Maf and a new turbo into it..

BUT then I called the shop that tested my car on the computer and he basically told me if I wanted to "re-test" the car it was going to be another charge so tonight i'm going to order the vag com from ross.. I mean that shop charged me 90 bucks for the other test of 15 - 20 minutes and so the 250 then i'll have the program.. for both cars..

So was it the Maf being plugged and unplugged (it tested within spec at the shops) or was it the turbo being "messed" with the vacuum back and forth and then it cleared itself or did I just leave a vacuum line loose on the actuator..

Oilhammer I checked the one way vacuum valve today and it seems to be working. And the car's actuator moves as soon as you turn the car on so I think it's holding vacuum.

I appreciate your help and i'll get you those test results when I get that cable in the mail.

Could it be the fuel pump in the tank not suppling enough fuel to the car? Maybe screen is plugged or something? one mechanic said he checked on the computer and said he ran an ohm test on it and it was fine. I just don't understand what sitting in a dealer parking lots after a timing belt change and driving it would slowly be taking away fuel economy and power with it and not show up anywhere..

thanks
 

whitedog

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Location
Bend, Oregon
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2004 Jetta that I fill by myself
Could it be the fuel pump in the tank not suppling enough fuel to the car? Maybe screen is plugged or something? one mechanic said he checked on the computer and said he ran an ohm test on it and it was fine.
He tested the pump motor but not the pump. To test the pump, it needs to pump a certain amount of fuel in a certain amount of time.
 

vwztips

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2005 Passat GLS Wagon TDI 5 spd manual w/BSM delete 2011 Tiguan TDI/DSG 2005 Audi A4 Avant 6MQ TDI 2011 BMW X5 35d
Once you check torsion value let us know.
 

twfarms

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ml washington
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05 passat wagon 06 bug
good point

That sir is a good point that I didn't think about the tank pump. The only reason I've thought about it is that it's making a slurpy noise sometimes when turning the key on but machinery and stange noises.. lol

And vwztips.. tomorrow first thing in the a.m. i'm ordering the cable from ross-tech and so i'll have those numbers this weekend (as long as I can figure out the computer program that is:rolleyes:)

tw
 

vwztips

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2005 Passat GLS Wagon TDI 5 spd manual w/BSM delete 2011 Tiguan TDI/DSG 2005 Audi A4 Avant 6MQ TDI 2011 BMW X5 35d
The noise form the tank is normal in some cars and non-existent in others, so don't worry about it.
 
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