2.5 v6 tdi very poor mpg?

[phil18_1]

hi, just brought a 2.5 v6 tdi passat (tiptronic), i have changed all filters in the last few days as it needed servicing. i know it is a v6 but im only getting 18 - 20 mile per gallon is this right? as ive read that it should do 30 - 35.

thanks phil

[snapdragon]

No that's really bad, I have the same car and the worst I get is 25mpg in traffic jams, and I thought that was bad. If I drive in urban areas when it's quiet and drive sensibly, I get 32mpg. I have had lots of problems with the car though, so based on that...

Here are some tests for you to do.


Take the plastic cover off the top of the engine (4 x 10mm nuts)
Open the drivers window as you need to start the engine and quickly look at something on the engine.


Look at the silver metal 'cup' on top of the turbo (yours will probably have a metal shield over the turbo) and look below it, there is a black rod that controls the vanes of the turbo, start the engine and this rod should take about 2 seconds to rise about an inch and stay there.

Next follow the pipe you can see on this 'cup' to your N75 valve which is mounted on the bulkhead near the fuel filter (just on the left out of shot) I think the pipe is the middle one of three on the valve. Pull it off and then suck it with your mouth and watch the rod you watched before, you should be able to make it move, and you shouldn't be able to suck air through (it should hold a vacuum) also try blowing, the pressure should build up but not leak out. If this is all OK, then this cup doesn't have a burst diaphragm.


Next look at the air pipes which connect to the bulkhead, roughly in the centre above. There is a one-way valve which is half-white and half black. Remember which way this goes and pull it off and suck and blow through it. Air should only go one way.

Next look at the silver 'cup' on top of the EGR valve, this is the one roughly in the middle of the picture above, with the engine running, pull the vacuum pipe off, you should hear a metallic ping as the valve snaps shut. Now that you know it is shut (assuming you heard the ping) put a bolt or some other bloackage in the vacuum pipe and tie it down, leave it unplugged, and try the car with the EGR valve disabled.

Hopefully you will find something wrong!
Good luck!

[phil18_1]

No that's really bad, I have the same car and the worst I get is 25mpg in traffic jams, and I thought that was bad. If I drive in urban areas when it's quiet and drive sensibly, I get 32mpg. I have had lots of problems with the car though, so based on that...

Here are some tests for you to do.


Take the plastic cover off the top of the engine (4 x 10mm nuts)
Open the drivers window as you need to start the engine and quickly look at something on the engine.


Look at the silver metal 'cup' on top of the turbo and look below it, there is a black rod that controls the vanes of the turbo, start the engine and this rod should take about 2 seconds to rise about an inch and stay there.

Next follow the pipe you can see on this 'cup' to your N75 valve which is mounted on the bulkhead near the fuel filter (just on the left out of shot) I think the pipe is the middle one of three on the valve. Pull it off and then suck it with your mouth and watch the rod you watched before, you should be able to make it move, and you shouldn't be able to suck air through (it should hold a vacuum) also try blowing, the pressure should build up but not leak out. If this is all OK, then this cup doesn't have a burst diaphragm.


Next look at the air pipes which connect to the bulkhead, roughly in the centre above. There is a one-way valve which is half-white and half black. Remember which way this goes and pull it off and suck and blow through it. Air should only go one way.

Next look at the silver 'cup' on top of the EGR valve, this is the one roughly in the middle of the picture above, with the engine running, pull the vacuum pipe off, you should hear a metallic ping as the valve snaps shut. Now that you know it is shut (assuming you heard the ping) put a bolt or some other bloackage in the vacuum pipe and tie it down, leave it unplugged, and try the car with the EGR valve disabled.

Hopefully you will find something wrong!
Good luck!

hi could you point me in the right direction where the rod is on the pic, carnt see it. i have tested where the pipe comes off the n75 valve i carnt suck or blow no air come though or goes in but carnt see the rod again. the black and white valve i can only blow nothing come though when i suck. going to test the egr l8a

thanks phil

[snapdragon]

Look at the second pic, and shine a small torch under the silver cup on the turbo, near the oil filter. The silver cup has a diaphragm in it which when vacuum is applied with pull up a rod coming out the bottom of the cup. This then pulls the lever coming out of the turbo housing. Inside the turbo, this lever is moving a large ring which is engaged with around 12 static vanes which drirect the exhaust flow at different angles of attack towards the impeller.

Also, it is the blue painted part here....

even better!

[phil18_1]

Look at the second pic, and shine a small torch under the silver cup on the turbo, near the oil filter. The silver cup has a diaphragm in it which when vacuum is applied with pull up a rod coming out the bottom of the cup. This then pulls the lever coming out of the turbo housing. Inside the turbo, this lever is moving a large ring which is engaged with around 12 static vanes which drirect the exhaust flow at different angles of attack towards the impeller.

Also, it is the blue painted part here....

even better!

thanks for replying fast, yea found it , when i start it it does not move it stays like how it is in your pic.

is this the prob how do i solve it

thanks phil

[snapdragon]

Mine moves up now but didn't used to when I had problems.
If you take the middle pipe off the N75 and suck as though you are trying to suck icecream up a straw, does the actuator rod move then. It is hard work, but you should be able to suck it up all the way, and no air should be sucking into the cup, as it should be airtight. Also make sure you can't blow.

If that is OK, the actuator should be OK, but if you want to remove it, it's not that hard, there are 2 x 10mm nuts holding it onto the braket, they can be undone with a ring spanner (best to put some kitchen towel down to catch them if you drop them) and then you need to pull a circlip off at the bottom of the rod with needle-nosed pliars, be very careful and put cloths under, as if you drop this, you can't get new ones.
Once off, you can test it moves OK, and test the lever on the turbo itsself, it should be effortless to move, almost as though disconnected inside. Sometimes the mechanism jams or gets sooted up and the lever is sticky and binds.

If you don't feel like removing the actuator, then you could replace the N75 valve on the bulkhead, they are about £33. Whatever it is, it sounds most likely to be a vacuum problem, or possibly the turbo, maybe the MAF sensor (airflow meter) but I would still expect the actuator to move, is it possible for you to watch this again while someone else starts the car, blips the throttle a few times and switches off.

To go any further, you really need to check the vacuum system and hoses for leaks using a mightyvac (hand-held vacuum pump with guage) and VAG COM software to tell the ECU to actuate the N75 valve for testing, and also check the injection timing is within specs.

[phil18_1]

Mine moves up now but didn't used to when I had problems.
If you take the middle pipe off the N75 and suck as though you are trying to suck icecream up a straw, does the actuator rod move then. It is hard work, but you should be able to suck it up all the way, and no air should be sucking into the cup, as it should be airtight. Also make sure you can't blow.

If that is OK, the actuator should be OK, but if you want to remove it, it's not that hard, there are 2 x 10mm nuts holding it onto the braket, they can be undone with a ring spanner (best to put some kitchen towel down to catch them if you drop them) and then you need to pull a circlip off at the bottom of the rod with needle-nosed pliars, be very careful and put cloths under, as if you drop this, you can't get new ones.
Once off, you can test it moves OK, and test the lever on the turbo itsself, it should be effortless to move, almost as though disconnected inside. Sometimes the mechanism jams or gets sooted up and the lever is sticky and binds.

If you don't feel like removing the actuator, then you could replace the N75 valve on the bulkhead, they are about £33. Whatever it is, it sounds most likely to be a vacuum problem, or possibly the turbo, maybe the MAF sensor (airflow meter) but I would still expect the actuator to move, is it possible for you to watch this again while someone else starts the car, blips the throttle a few times and switches off.

To go any further, you really need to check the vacuum system and hoses for leaks using a mightyvac (hand-held vacuum pump with guage) and VAG COM software to tell the ECU to actuate the N75 valve for testing, and also check the injection timing is within specs.

The lever of the actuator was jammed so i took the actuator off i had to really pull n push the lever to free it once the lever was free to move, i put it back together. now i can see the lever move up n down when i start the car and rev the engine it move up n down continuous as it should. so im going to see what happens with the mpg over the next few days i got a long motoway journey to do tomorrow night so ill let you now what happens.

again thanks for quick replys i will let you no soon thanks Phil