22 MPG??

[Hayze]

Well, there's a culprit. Having the down pipe missing or loose shouldn't hurt fuel economy, but with the intake you have... It's just gonna suck all that hot exhaust right back in... And since it's inert gasses.... It won't combust well.

You can call it a poor mans EGR mod, i mean EGR's do the same thing only without an air filter and a maf sensor.

 

[Hayze]

So as the title states, i’m averaging 22MPG in my 2004. I have an EGR delete, CAI, straight pipe, and an upgraded turbo (VNT17) without a tune, but when I first got it I was averaging 50MPG reliably.
(Sorry in advance for the long post)

I first noticed this change after my dogbone motor mount broke in half, replaced it (without driving it more than 2 miles very gingerly), and now i have a bit of white smoke on startup from under the hood and also out the exhaust. I did an oil change and added Liqui-Moly motor oil saver, but this didn’t really change anything. It runs incredibly smooth other than on a startup, when it studders and smokes for less than 30 seconds and then runs fine. On top of all this, occasionally my veins will stick on a cold start, but if i turn it off and back on while driving it immediately fixes the issue (this has been happening since i bought it). I’m kinda stumped as I can’t really tell where to start here since I was getting fine mileage before the dogbone, but not after, even though I looked around to try to make sure nothing else was broken. If anyone has any suggestions on how to tackle this please let me know, but i don’t want to just throw parts at it without reasonable explanation. Thanks in advance!

Its also possible you have leaking injectors.
If your injectors are leaking you can have poor fuel mileage.
to verify this look at the top of your engine around the connectors for injectors.
If it looks like its wet around the injectors all the time then they are leaking past the seals and those seals have to be replaced.
Possibly injectors as well.

never add additives to engine oil, specially moly. Moly is well known for killing diesel engines. including semi trucks.
Only time i would trust an additive in engine oil would be a small cup of lucas thats it.

cars around the year of 2004 have had issues with vnt actuators.
But likely your low mileage is going to be 1 of 2 things.

- Boost leak in your charge pipes or intercooler,
- leaking injectors

What i would do is inspect all my charge pipes and boost hoses for any cracks, breaks, leaks, etc.
You can also have oil resting on the lower level of your intercooler and the boosted air is trying to work its way past the resting oil in your charged air from the turbo.

Hopefully this information will give you some insight and help. Diesel cars are higher maintenance than gas cars trust me. Its mainly because the technology difference between the 2 to make them operate.

 

[Nero Morg]

Diesels operate under heat, its compression, hot air actually helps with compression. There is no combustion thats for gas.
Not to mention the radiator in these cars are also intercoolers. As long as your turbo is not injesting 900 degree heat the intercooler will keep the current temps the intercooler is at regardless of what intake you have on the car.

You obviously didn't read or didn't comprehend what I was saying.

With a sizeable exhaust leak in the engine bay and a CAI, the engine will injest INERT gasses (gasses that do not combust) which will affect fuel economy. It's essentially like having the EGR stuck partially open all the time. Also injecting hot air will affect it, by throwing off the fuel tables, making the ECM see the intake air is hot due to said exhaust gasses being injested.

Then you mention the radiator is the intercooler? What?? No they aren't! Radiator radiates heat from the coolant. Intercooler cools intake charge air. The intercooler can also get heat soaked, it only has a certain amount of capacity that it can cool.

Then you bring up maf and regens, totally two different animals there, completely different ECM's. These cars are giant turds with the maf disconnected (excluding maf delete tunes)

You are correct about leaking injectors and boost leaks, but I take the time to type all this up to prevent the spread of misinformation.

 

[AndyBees]

Hot air is less dense than cold air ... thus, the amazing things a good Inter Cooler will do for any Turbo Charged Internal Combustion Engine.
The Original Poster's car is an 04 which "had" an excellent OE Cold Air Filter System.

 

[Hayze]

Then you mention the radiator is the intercooler? What?? No they aren't! Radiator radiates heat from the coolant. Intercooler cools intake charge air.

I fast typed that part by mistake,
They would be stacked together,
going to edit that comment and fix that part.

 

[Nero Morg]

Newer cars they are stacked, some have a water cooled intercooler, but these cars have a side mount.

 

[AndyBees]

My Dodge and Tiguan, have them stacked with the AC condenser out front and the Dodge has a transmission cooler sandwiched in there somewhere. In fact, I had to change the fluid pipe on it today (cracked flare).

 

[oilhammer]

That picture is a HOT air intake, not the factory thermostat-controlled cold air intake. I'm always at a loss as to why this is so hard to understand. The air under the hood is HOT, as all of it has passed through the A/C condenser, intercooler, and radiator. All of the heat exchanged is now the hot air that is being drawn into the engine, instead of the channeled in air from in front of the car.

 

[IndigoBlueWagon]

The OP seems to have taken a break from this thread, which might be a good thing as there's some incorrect and not helpful info here (not from you, Brian ).

This car is using approx. twice as much fuel as it's supposed to. A crappy CAI or dirty injectors aren't going to have that impact. Something else is seriously wrong, if the fuel consumption numbers are accurate.

 

[matttdi]

The OP seems to have taken a break from this thread, which might be a good thing as there's some incorrect and not helpful info here (not from you, Brian ).

This car is using approx. twice as much fuel as it's supposed to. A crappy CAI or dirty injectors aren't going to have that impact. Something else is seriously wrong, if the fuel consumption numbers are accurate.

thank you lol. i fixed the exhaust and haven’t driven enough to tell if that is the only thing that’s going to fix it. this thread took a spiral downhill fast

 

[matttdi]

I’m also starting to think maybe it’s directly fuel related. When starting the car it takes a few cranks, then runs rough like mentioned before. Since the previous owner straight piped the car, I can see all the glorious (white) smoke that comes billowing out after. Could this be lift pump or tandem pump or injectors related? I know a few people said leaky injectors. Thanks in advance.

 

[AndyBees]

White Smoke generally equals too advanced timing or not enough air ....... and, can be both, depending on the circumstances.

So, as suggested, the Torison Value needs to be checked! ......... scan for DTC's would be a good start too!

How many miles on this car?

The seasoned/experienced TDI enthusiast here are close to purist. They definitely frown on Cold Air Intakes ......... as you have come to see! The OE air-box and filter are as good as they come when you think Cold Air and Filtering!

 

[matttdi]

White Smoke generally equals too advanced timing or not enough air ....... and, can be both, depending on the circumstances.

So, as suggested, the Torison Value needs to be checked! ......... scan for DTC's would be a good start too!

How many miles on this car?

The seasoned/experienced TDI enthusiast here are close to purist. They definitely frown on Cold Air Intakes ......... as you have come to see! The OE air-box and filter are as good as they come when you think Cold Air and Filtering!

Just clicked over 205k this morning. Sounds to me like it might be more cost efficient to pass this car off to someone else rather than throwing more time and money at it.. was supposed to be my reliable daily driver but it’s more expensive on fuel than my corvette at this point

 

[JB05]

Might be a good idea to check the tandem pump. Any external leaks would be obvious, but not certain as to how to check for internal leaks.
Maybe disconnects the vacuum hose to see if oil as seeped in.

 

[Nero Morg]

Usually running rough and white smoke at start, but smooths out, usually means air intrusion that bleeds in overnight.

 

[oilhammer]

White smoke, assuming it is diesel-smelling, is from bad combustion. Some of this is normal (it even says this in the manual, if anyone bothers to read it). But it is usually limited to a small "start up puff", and worse in cold weather. All of my TDIs do it, to some extent. Usually it is not enough to notice from the driver's seat, although the BHW does it enough below 30 F that you almost always notice it. It always has, since it was brand new.

But if you have large constant plumes, accompanied with misfires, then you have something else going on (keep in mind, a quarter million mile car after sitting outside overnight at 0F may do this no matter what).

If there is air (loss of prime) getting into the fuel system somehow, you can have this same sort of condition. Because the injection system cannot properly atomize the fuel if it is trying to compress a gas (air) at the same time as trying to squirt a liquid (diesel) under high pressure.

Loss of prime is usually easy enough to rule out. Because once the engine is running, and it has pushed the air out, it will typically hold that prime for at least a little while. So if as soon as it starts to run normally, and most of its start up smoke and fits are done (maybe ~15 seconds?), shut the engine back off and wait 10 minutes. Start it again. If it starts right up, and doesn't exhibit the same symptoms, it probably is a loss of fuel prime from sitting.

Keep in mind, on the PD, loss of fuel prime can actually happen internally in the engine... one or more of the injector seals could be weeping internally, allowing a loss of fuel prime in the fuel galley in the head itself (it doesn't take much volume... a tiny bit is all) and it leaks into the engine and mixes with the oil. If it is a small enough amount, you really won't ever know it, as it won't dilute the oil *that* much although it may contribute to some faster oil consumption.

 

[matttdi]

White smoke, assuming it is diesel-smelling, is from bad combustion. Some of this is normal (it even says this in the manual, if anyone bothers to read it). But it is usually limited to a small "start up puff", and worse in cold weather. All of my TDIs do it, to some extent. Usually it is not enough to notice from the driver's seat, although the BHW does it enough below 30 F that you almost always notice it. It always has, since it was brand new.

But if you have large constant plumes, accompanied with misfires, then you have something else going on (keep in mind, a quarter million mile car after sitting outside overnight at 0F may do this no matter what).

If there is air (loss of prime) getting into the fuel system somehow, you can have this same sort of condition. Because the injection system cannot properly atomize the fuel if it is trying to compress a gas (air) at the same time as trying to squirt a liquid (diesel) under high pressure.

Loss of prime is usually easy enough to rule out. Because once the engine is running, and it has pushed the air out, it will typically hold that prime for at least a little while. So if as soon as it starts to run normally, and most of its start up smoke and fits are done (maybe ~15 seconds?), shut the engine back off and wait 10 minutes. Start it again. If it starts right up, and doesn't exhibit the same symptoms, it probably is a loss of fuel prime from sitting.

Keep in mind, on the PD, loss of fuel prime can actually happen internally in the engine... one or more of the injector seals could be weeping internally, allowing a loss of fuel prime in the fuel galley in the head itself (it doesn't take much volume... a tiny bit is all) and it leaks into the engine and mixes with the oil. If it is a small enough amount, you really won't ever know it, as it won't dilute the oil *that* much although it may contribute to some faster oil consumption.

I have this exact problem. When cold it’s a plume of white diesel smelling smoke, but i can get it warmed up and it’ll run fine and shut it off for 10 minutes after driving and it doesn’t do it again. Sounds like i’m getting air, but any sure fire way to diagnose where? I have been cycling the key 5-10 times every morning to stop it from having this issue, and it has fixed it 90%, but i’d rather not have to do that every morning to avoid the misfires and plume of smoke. Any suggestions?

 

[mittzlepick]

Mine smokes on startup yet 40 43 mpg. If things were leaking fuel externally you would have seen a 20 mpg drop in the driveway

 

[ssullivan]

Ask your tuner to give you more Start IQ for cold starts.

 

[ssullivan]

Back to the 22mpg, there were a bunch of things to check in this thread that can cause low mpg,

simple one is dragging parking brake.

 

[Gothmolly]

My 02 was leaking fuel from the low-pressure return lines. Sure-fire way to lose mpg.