Emissions failure caused by VFAQ 2g intake tube mod

[93'colttsi]

Well I had to get my 2G dsm through emissions (British Columbia, Canada) (IM240 drive cycle on awd dyno) Anyways, I put some new BPR6ES in there, (stock boost plugs) filled it with a fresh tank of husky 91 octane and took it for a rip on the highway. Car ran awesome, pulled hard for stock boost. Took it through emissions testing and ended up failing the IM240 on hydrocarbons (over twice the limit). CO and NOX were way below the average limits, but the HC was high. Inspected the driving trace and found that the HC's spiked way high on deceleration. (throttle closed after a cruise or acceleration). Sort of a weird failure. At the time of the HC spike on decel the o2 levels also went very high indicating a lean condition causing a lean misfire (cause of big HC spike). I have checked for vac leaks and boost leaks, which none were found. Luckily I am a emissions diagnostic technician, so I have a bit of a head start on diagnosing problems like these.

I was leaning toward a defective/sticking EGR valve causing a vac leak on throttle closure. Inspected the vac line routing and everything looks like it's hooked up properly. I got a few spare EGR valves laying around.... or I could always try to block off/disable the egr valve and re-test, NOX was very low, so I do have some room there. preferably I would like to retain all emission equipment.

REPAIR:
Well... luckily I had access to a gas analyzer and I could duplicate the high HC/CO problem on my dsm on decel. I blocked off the egr valve vac lines. Still hitting 3000+ PPM of HC on a throttle closure from 2500 RPM in neutral. Blocked off PCV. Same thing, then I figured maybe its the BOV, changed the 1g BOV with a spare I had laying around. Same thing again.

Well next thing I remembered is that I had installed a "shortend and cut" BOV recirc tube that fits into the rubber intake snorkel. The mod is posted on VFAQ in a few locations and says is a great way to get more power. What it doesn't say is that it will cause you to FAIL emissions.

What was happening is that due to the pipe not extending down inside the intake snorkel, and directing the BOV air down towards the turbo on throttle closure, the air would instead shoot out from everywhere inside the snorkel, and a lot of it was going right into the MAF sensor giving a false reading and it would dump fuel thinking its flowing way more air then it was every time you let off the gas. I rigged up a temporary "longer" hose with some big heater hose and had the BOV directed back at the turbo inside the intake snorkel. I didn't change anything else.

Well she passed no problem this time. WHY DIDNT ANYONE TELL ME!! ahhahaha At least its done emissions testing for good now (British Columbia ends emissions testing dec 31st, 2014)

My old aircare/emissions numbers (IM240 awd dyno test)
Hydrocarbons(HC) : 1.32 g/km FAIL ( 0.5 g/km limit)
Carbon Monoxide(CO) : 4.14 g/km PASS ( 9.32 g/km limit)
NOX : 0.24 g/km PASS ( 1.24 g/km limit)


New aircare/emissions numbers
Hydrocarbons(HC) : 0.22 g/km PASS
Carbon Monoxide(CO) : 0.51 g/km PASS
NOX : 0.26 g/km PASS

Obviously you can see that this would affect your gas mileage big time if your driving a lot of city. Of course at WOT you will get a bit of power by removing the tube, but then gas mileage isn't the issue.


Just a heads up to anyone using a 2G intake tube, or many aftermarket intakes (dejon?) with recirculating BOV may have the same issue with emissions. this could also happen to a MAF 1g with a aftermarket intake, but I have never had this problem with 1G cars/intake snorkel due to the different design where the BOV returns farther down the tube nearer to the turbo.

Some pics

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[Seamus]

Great detective work. This is a great driveabity/fuel economy info for people using an air flow meter, regardless of their areas emissions guidelines.

 

[T is for TURBO]

Sorry, but I'm not sure I buy this. Many people have had this mod for years and this is the first time I have ever hear of it causing someone to fail their emissions. Not to mention, your bov only opens under vacuum (unless it is leaking), this vacuum would pull any bypassed pressure back through the turbo and not out the MAF.

on decel the o2 levels also went very high indicating a lean condition causing a lean misfire (cause of big HC spike). equipment.

Also, our cars always go "lean" on decel. The ECU shuts the injectors off.

 

[93'colttsi]

Sorry, T is for Turbo. Let me clarify a bit better.

Not to mention, your bov only opens under vacuum (unless it is leaking), this vacuum would pull any bypassed pressure back through the turbo and not out the MAF.

1G BOV's are well known for being open at idle. Not sure if the stock plastic 2G BOV does this, as I have never ran one. After a high RPM cruise (in vaccum) followed by a throttle closure you have all that air rushing into the engine, and then all of a sudden the throttle plate closes pretty much creating two separate chambers. The intake manifold suddenly pulls into a hard vaccum (this is where the BOV vac line hooks up) and the air on the outside of the throttle plate pretty much hits a wall and being the BOV is open, the air only has one place to go, out the BOV and back into the intake pipe. I think you are thinking the air near the BOV is being pulled into a vacuum as well, but it is not.

Being that I have access to a 5 gas analyser I was able to duplicate the conditions where the High HC and CO conditions were happening. I installed the longer tube back into the 2g intake (directs BOV air back at turbo) and the HC and CO levels DROPPED HUGE on throttle closures. Im talking like going from reading 3500 + ppm to around 100-200 PPM. Just to be sure I re-installed the "modified, shortend" recirc tube back into the 2G intake (without changing ANYTHING else). Well what do you know? back to spitting out 3500+ PPM on higher RPM (3000-4000RPM) in vacuum throttle closure. I did this two more times just to make sure 100% that it was indeed the internal recirc pipe inside the intake causing this.

Now, if your running SD, this would not be a issue as SD has nothing to do with airflow readings and everything to do with pressure and air temp.



And yes, the ECU is designed to shut off the injectors on a decel 0% throttle while the car is moving. when the car is idling obviously this can not happen otherwise the engine would stall, and the ECU could totally add fuel when it sees elevated MAF signal. now im no expert on how exactly the ECU calculates when and how exactly it decides to shut off the injectors, but it has to do with VSS readings and TPS readings for the most part im sure. Now from what I have found there must be also the MAF reading put into that. To confirm this I could have used a scope on the injectors, as well of the MAF and moniter the HZ and duty cycle. but from the testing I did, the failure was DEFINALTY cause due to the BOV air going back through the MAF.

Now obviously every car is different, and my car may have something special that causes this issue only on my car, but I seriously doubt that. Im sure also that with aftermarket engine managment you could tune around the problem as well playing with VE tables and the such. It could be also due to how exactly I cut my pipe down. If you look at my picture it almost directs the air back at the MAF from the piece protruding out.

I dont think a lot of people have actually sat down with a gas analyser and started testing these sorta things. But the numbers dont lie!

Here is a image of my drive trace on the emissions failure. The grey line in the background is vehicle speed and the colours are keyed at the top. You can clearly see the high HC spikes on decel situations if you look at it.

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Now for the pass, again ALL I changed was put the tube back inside the 2G intake, directing air back at the turbo instead of being cut off.

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what other ideas do you have that could cause this?