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Old March 1st, 2018, 14:57   #1
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Default Can't pass California Snap Test for Smog

Should a 2004 Passat TDI put out any smoke when throttle is pressed from idle to 2500 RPM? Mine puts out a small puff, but once RPM's get up, the smoke is no longer there. Smoke is black, so probably un-burned fuel. I did remove both mufflers for the sound, and VW service told me they found nothing wrong with the car except missing mufflers, and wanted me to put those back on for $1500. Could I have a oil filled intercooler slowing airflow, or a blocked EGR valve? Neither of them have ever been looked at. I have one month to fix issue. Thanks,
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Old March 1st, 2018, 15:06   #2
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When did they start that test?
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Old March 1st, 2018, 16:00   #3
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california'ed. I hear shops jump up and down when they hear of emission failures in CA. Cha ching.
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Old March 1st, 2018, 16:17   #4
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Find some biodiesel and maybe put just that in the tank before the re-test. It might be worth a shot.
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Old March 1st, 2018, 16:32   #5
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As far as exhaust goes, barring fixing everything else, couldn't you get a system from another car of the same model in the wrecking yard for a lot less money, and bolt that in for testing purposes?

I don't know BEW engine management or typical behavior, so I can't even venture a guess as to normal operation.
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Old March 1st, 2018, 16:51   #6
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The smoke is not the result of the missing mufflers. You can pay VW $1,500 but it will still fail the snap test.

You might have some good results from biodiesel and/or cetane boost additive like PowerService silver bottle.

If all else fails and everything engine and fuel delivery related is in good working order, you might want to consider talking to a tuner about cleaning the car up a bit so that it will pass emissions.
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Old March 1st, 2018, 17:33   #7
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I thought CA just plug in the OBDII and run a diagnostic that way. Since getting rid of the pipe sniff test, I've never seen a tech "Snap test."
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Old March 1st, 2018, 17:42   #8
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I did remove both mufflers for the sound

Did you remove the Cat?
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Old March 1st, 2018, 20:04   #9
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There are three reasons that you would have a puff of black smoke when you hit the throttle.

1) The EGR is sticking open a bit. The throttle will lag, then suddenly, BOOM! you have a power surge, which can smoke. Clean the EGR valve. Less likely...

2) You have a Turbo Actuator rod that is closing too much. When you hit the throttle, the actuator wants to open the VNT on your turbo, but the the vanes that are closed too much, and the exhaust pressure keeps the vanes closed...It smokes and belches. Let the pedal off, then back on, it passes the crisis and the vanes open correctly. There is a goofy wire lasso we make to correct that problem. Somewhat likely...

3) Your cam is worn out. Remove the valve cover and look for the tell-tale signs of galling on the base circle of the cam. If you see this adverse wear, and also, the tops of the lobes have sharp edges, especially on the exhaust lobes (1, 3, 6 and 8), you have a worn cam. Because of the reduced lift of the cam, not enough boost pressure comes in with the associated fuel charge. This causes the first few seconds of engine revving to puff black smoke. Very likely....

In CA, they want to eliminate diesels. We do have a cam kit, if you like. The other 'fixes' are just a matter of know-how.

Let us know if we can be any additional help.
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Old March 1st, 2018, 20:32   #10
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Quote:
Originally Posted by caideN View Post
I thought CA just plug in the OBDII and run a diagnostic that way. Since getting rid of the pipe sniff test, I've never seen a tech "Snap test."
Never was a sniff test on Diesels. Last time I went there was no snap test.
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Old March 2nd, 2018, 05:28   #11
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Cannot speak to the CA test procedure, but my own BHW has always had a more smoky exhaust at takeoff than other TDIs, and it seems pretty typical for them. They have a HUGE charge air tract, so there is a point where the ECU can put fuel in, but the turbo has not had a chance to get the air the ~8 feet back around to the intake.

What I find is running the car hard (doing some hard floorboarded runs, up to redline) once the car is warmed up, will help blow out any crud and help get the car cleaned up.

You may also remove the EGR valve and make sure it is clean. The EGR is on at idle (unless it idles for a few minutes), so if it is a bit gunked up, the air flow will be less than ideal right off idle.

The BEWs and BRMs don't seem to ever exhibit this quick tip in puff like the BHWs do.
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Old March 2nd, 2018, 09:22   #12
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Another possibility could be worn or dirty injectors.

If the spray pattern is not good, maybe you'd get a bit of smoke.

A cleaning with Lubro Moly Diesel Purge might help if the injectors just need cleaning. It needs to be run directly from the can, full strength.

If they're worn, that's a more costly problem requiring an expert to overhaul the injectors.
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Old March 2nd, 2018, 09:28   #13
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Did the inspector tell you what the specific failure was? Did he say smoke?
I would try OHs workaround -
What I find is running the car hard (doing some hard floorboarded runs, up to redline) once the car is warmed up, will help blow out any crud and help get the car cleaned up.

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Old March 2nd, 2018, 09:59   #14
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Kind of ironic that smoke is actually not a major contributor of "smog" per se, but a specific ratio of HCs (VOCs) and NOx.

Nevertheless, all the usual suspects in terms of maintenance and mechanical condition have been thoroughly covered. Once these are addressed, I suggest to run a tank or two of high % Biodiesel or Propel, and I also second and third the suggestion to give it a real good ol' Italian tune up driving all the way to the inspection station.
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Old March 2nd, 2018, 10:12   #15
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Quote:
Originally Posted by oilhammer View Post
Cannot speak to the CA test procedure, but my own BHW has always had a more smoky exhaust at takeoff than other TDIs, and it seems pretty typical for them. They have a HUGE charge air tract, so there is a point where the ECU can put fuel in, but the turbo has not had a chance to get the air the ~8 feet back around to the intake.
What I find is running the car hard (doing some hard floorboarded runs, up to redline) once the car is warmed up, will help blow out any crud and help get the car cleaned up.
You may also remove the EGR valve and make sure it is clean. The EGR is on at idle (unless it idles for a few minutes), so if it is a bit gunked up, the air flow will be less than ideal right off idle.
The BEWs and BRMs don't seem to ever exhibit this quick tip in puff like the BHWs do.
What oilhammer said. "Drive it like you stole it" applies.

I have never heard of CA doing a snap test for diesel cars. The tech noticed the smoke and the amount for your car might actually be normal. The tech probably works on gassers most of the time. That doesn't imply there actually is snap test that it has to pass.

If the car has to pass a snap test in CA, I have an idea for an electrical mod that might help. In the CR TDIs and in my BMW diesels, you absolutely cannot snap accelerate them to full throttle no matter how fast you slam the fuel quantity request pedal to the floor (can't call it a "gas" pedal ). The rate of throttle change as seen by the ECU is carefully controlled during by design to prevent making smoke. The ECU does a quick but carefully controlled ramp up to full throttle during a snap event instead of doing it as a step function. The PDs and older TDIs can be snap accelerated but CR TDIs cannot be. The idea I had for a mod on PDs and older TDIs is to add capacitance to the go-pedal circuit to slow down the throttle input to the ECU to prevent making smoke during a snap test. It will roll into full throttle instead snapping to full throttle when you stomp on the pedal. It's all about controlling the rise time of the throttle input to the ECU.

I've never actually tried this as an electrical mod but I was thinking about it given that our cars use a drive by wire throttle system.


Last edited by n1das; March 2nd, 2018 at 14:04.
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