Can fuel tank vent valve cause random smoking? - N54Tech.com

phubar · **Can fuel tank vent valve cause random smoking? -** 03-30-2015, 09:06 PM

Hello all, for the past month I have been battling random puffs of smoke (yes I know probably turbos) from the tail ***** and from under the hood (from DCIs) while stopped, sometimes 30 seconds after startup, sometimes there will be a cloud while driving, some days it wont even do it at all, there isnt really a pattern to the smoke. The smoke is generally blue sometimes more pale than others. I understand there is a 99% chance its the turbos but have to make sure, while I hunt down everything I need to replace the turbos might as well rule out any other pcv/vacuum issues.

My valve cover gasket was leaking really bad so I replaced the whole valve cover (new kit comes with everything). It had no effect in the random smoke but it cured some other issues.

-Walnut blasting done, no effect.
-Vent hose replaced, no effect.
-Pulled ***** less *****, no oil.
-Typical oil film/residue on chargepipe/intercooler.
-BMS catch can made it horribly worst, like a coal powered car. Also vented to air, same result.
-RB PCV, no effect.
-Replaced vacuum lines, no vacuum leaks.
-INPA shows no codes whatsoever.

Car pulls strong and it has no issues other than the random smoke. In the last 5k miles only lost about 1/2 qt of oil, measured by recovering oil from oil change. I have not added any oil since last oil change and no one else touches my car.

While troubleshooting some more today, I noticed a continuous clicking I had never heard before and traced it down to the fuel tank vent valve http://www.ecstuning.com/ES2138069/ disconnected it and reconnected it, it only clicked once after that. This valve connects to the throttle body after the butterfly, according to the theory of operation, it should only open momentarily to apply slight vacuum to the fuel tank. I also noticed a few days ago my fuel tank cap doesn't lock tightly in place, it clicks as if its locked but its actually pretty loose and requires no effort to remove it. Now I realize both of this conditions should trigger a CEL but if the vent valve is randomly sticking and continuously cycling open, I see how it might "rob" the pcv system of the much needed vacuum to depressurize the motor and allow some oil to leak either through the valve stem seals or turbo seals.

I have already ordered the fuel cap since its inexpensive and the lanyard on mine is broke anyways.

Do you gurus think I might be on the right track here or am I a delusional lazy bum trying to avoid replacing the turbos lol

slanteyez · 03-31-2015, 11:37 AM

Sounds like turbos or headgasket. Blue smoke = Oil. Have you done a compression test and leak down test?

phubar · 03-31-2015, 11:56 AM

Thanks for the input but head gasket has different symptoms, coolant level remains the same since more than 15k miles ago. I've already covered all the basics and statistically in the forums turbos seals are usually the culprit when it comes to random smoke. I'm just exploring other possible maintenance items that might have influence on the seals leaking.
I cleaned the fuel tank vent valve yesterday and not a puff of smoke today not even a hint but it wouldn't be the first time it doesn't smoke for a couple of days.

BostonBeemah · 04-01-2015, 04:37 PM

Keep us updated if it comes back becuase I get that ticking sound as well on my car and have been having a lot of smoke lately with little oil consumption as well like you.

tofu · 04-01-2015, 05:16 PM

funny, i have a ticking and smoke that started after swapping out my HPFP. i forgot to reconnect that line and was too lazy to take everything apart to do it properly, so i did some finger contortions to try to get it connected again.

it also took FOREVER for me to get evap readiness when inspection time came.

thanks for the idea. maybe i didn't connect it properly.

phubar · 04-01-2015, 07:49 PM

Thank you guys the input. Just to clarify, the clicking sound is more of a piezoelectric whirring than a ticking, I mention this because between the valves, injectors and who knows what else, there are a lot of different "tickings" in my engine bay. If you are unsure, you can touch the vent valve and "feel" if its clicking or not. It's pretty obvious if it is. Also, whether it clicks or not, there is no easy way to tell if its stuck open or not.

I installed the new fuel filler cap today. Rubber gasket in the old cap is completely DRY and deformed.
Now there is a slight vacuum for a few seconds when opening the oil filler cap and also a slight change in the idle.

tofu · 04-01-2015, 08:09 PM

oh, the ticking i am describing is exactly this one

https://www.youtube.com/watch?v=ocuUhCuQXx8

it's clearly not injector/wastegate

phubar · 04-03-2015, 02:24 PM

Thats not the fuel vent clicking, the video says its the boost solenoid.

Update: my car doesn't smoke randomly anymore, however, it still smokes abundantly but ONLY in 1st gear and while coasting at 1K rpm, if I tap the gas pedal slightly it stops, if I slow down to where the RPMs drop below 1K the smoking stops also. Something specific happens at 1K rpms, now I just have to figure out what.

BostonBeemah · 04-03-2015, 02:32 PM

Quote:

Originally Posted by phubar

Thats not the fuel vent clicking, the video says its the boost solenoid.

Update: my car doesn't smoke randomly anymore, however, it still smokes abundantly but ONLY in 1st gear and while coasting at 1K rpm, if I tap the gas pedal slightly it stops, if I slow down to where the RPMs drop below 1K the smoking stops also. Something specific happens at 1K rpms, now I just have to figure out what.

I get the same noise as well. I belive that it is sticking valves or something like that. I think there's a bleeding procedure or something I've read where you hold the car at 3k for a couple minutes to make it go away. Have tried but nothing changed. My line next to the throttle body was on and I put it on and off a couple times to check. Car still smoking. I'm starting to think it's valve guide seals or turbos.

phubar · 04-03-2015, 02:50 PM

Do you notice any difference in idle or any wheezing when you open the oil cap? if not then you definitely have an issue with the PCV, my other n54 had a perfectly functioning PCV and there was a slight vacuum when opening the oil cap, when I got my current one, I noticed opening the oil cap didn't make a difference, after reading the forums I thought it was normal, now that almost every PCV component has been replaced, guess what? There is a slight vacuum when I first open the oil cap.
I'm not saying your engine has the same issue but definitely look into the PCV, unless your turbo seals or valve stem seals are too worn out, they shouldn't leak if the PCV is operating correctly.

BostonBeemah · 04-03-2015, 03:05 PM

Quote:

Originally Posted by phubar

Do you notice any difference in idle or any wheezing when you open the oil cap? if not then you definitely have an issue with the PCV, my other n54 had a perfectly functioning PCV and there was a slight vacuum when opening the oil cap, when I got my current one, I noticed opening the oil cap didn't make a difference, after reading the forums I thought it was normal, now that almost every PCV component has been replaced, guess what? There is a slight vacuum when I first open the oil cap.
I'm not saying your engine has the same issue but definitely look into the PCV, unless your turbo seals or valve stem seals are too worn out, they shouldn't leak if the PCV is operating correctly.

I think it's a combination of both. I had this issue and ended up blocking the pcv ports in the head and putting in the A&D fittings on the pcv to try and fix the issue with no luck. Same issue.

phubar · 08:36 PM

Update on my cars smoking issue for future reference: Installed aftermarket inlets, eliminated PCV heater and kept the flapper valve, replaced the original plastic tubing with 1" silicone hose. Im happy to report in over 1500 miles I have not seen any smoke whatsoever. My next step to completely obliterate any possible smoking or built-up crankcase pressure is to add a T to the fuel tank vent valve and run a line to the pcv check valve using the AD engineering fitting for a stronger vacuum at low load. I can't exactly explain why this works but my guess is as the piston rings wear out more pressure builds up in the bottom end.

PhilTrill · 01-03-2016, 10:39 AM

phubar, how many miles are on your vehicle?

FCobra94 · 01-04-2016, 09:45 AM

Quote:

Originally Posted by phubar

My next step to completely obliterate any possible smoking or built-up crankcase pressure is to add a T to the fuel tank vent valve and run a line to the pcv check valve using the AD engineering fitting for a stronger vacuum at low load. I can't exactly explain why this works but my guess is as the piston rings wear out more pressure builds up in the bottom end.

Nice! Glad you got it figured out. Interesting how your new setup (inlets) corrected the issue even though everything is still, pretty much, functionally the same..??

Yeah, the "T to PCV" is how RB is handling the low pressure side as well. One step past that, tapping the head would seal it up completely.

Your thoughts as to why the BMS CC can make symptoms horribly worse after install though? I've seen peeps mention that when faced with similar scenarios in a few past threads as well.